Wilson disease is a disorder of copper metabolism that can present with hepatic, neurologic, or psychiatric disturbances, or a combination of these, in individuals ranging from age three years to older than 50 years; symptoms vary among and within families. Liver disease includes recurrent jaundice, simple acute self-limited hepatitis-like illness, autoimmune-type hepatitis, fulminant hepatic failure, or chronic liver disease. Neurologic presentations include movement disorders (tremors, poor coordination, loss of fine-motor control, chorea, choreoathetosis) or rigid dystonia (mask-like facies, rigidity, gait disturbance, pseudobulbar involvement). Psychiatric disturbance includes depression, neurotic behaviors, disorganization of personality, and, occasionally, intellectual deterioration. Kayser-Fleischer rings, frequently present, result from copper deposition in Descemet's membrane of the cornea and reflect a high degree of copper storage in the body.

An abnormality of histiocytes, in which the cells take on a sea blue appearance due to abnormally increased lipid content. Histiocytes are a type of macrophage. Sea-blue histiocytes are typically large macrophages from 20 to 60 micrometers in diameter with a single eccentric nucleus whose cytoplasm if packed with sea-blue or blue-green granules when stained with Wright-Giemsa.

Werner syndrome is characterized by the premature appearance of features associated with normal aging and cancer predisposition. Individuals with Werner syndrome develop normally until the end of the first decade. The first sign is the lack of a growth spurt during the early teen years. Early findings (usually observed in the 20s) include loss and graying of hair, hoarseness, and scleroderma-like skin changes, followed by bilateral ocular cataracts, type 2 diabetes mellitus, hypogonadism, skin ulcers, and osteoporosis in the 30s. Myocardial infarction and cancer are the most common causes of death; the mean age of death in individuals with Werner syndrome is 54 years.

The term "galactosemia" refers to disorders of galactose metabolism that include classic galactosemia, clinical variant galactosemia, and biochemical variant galactosemia (not covered in this chapter). This GeneReview focuses on: Classic galactosemia, which can result in life-threatening complications including feeding problems, failure to thrive, hepatocellular damage, bleeding, and E coli sepsis in untreated infants. If a lactose-restricted diet is provided during the first ten days of life, the neonatal signs usually quickly resolve and the complications of liver failure, sepsis, and neonatal death are prevented; however, despite adequate treatment from an early age, children with classic galactosemia remain at increased risk for developmental delays, speech problems (termed childhood apraxia of speech and dysarthria), and abnormalities of motor function. Almost all females with classic galactosemia manifest hypergonadatropic hypogonadism or premature ovarian insufficiency (POI). Clinical variant galactosemia, which can result in life-threatening complications including feeding problems, failure to thrive, hepatocellular damage including cirrhosis, and bleeding in untreated infants. This is exemplified by the disease that occurs in African Americans and native Africans in South Africa. Persons with clinical variant galactosemia may be missed with newborn screening as the hypergalactosemia is not as marked as in classic galactosemia and breath testing is normal. If a lactose-restricted diet is provided during the first ten days of life, the severe acute neonatal complications are usually prevented. African Americans with clinical variant galactosemia and adequate early treatment do not appear to be at risk for long-term complications, including POI.

The phenotype of acid sphingomyelinase deficiency (ASMD) occurs along a continuum. Individuals with the severe early-onset form, infantile neurovisceral ASMD, were historically diagnosed with Niemann-Pick disease type A (NPD-A). The later-onset, chronic visceral form of ASMD is also referred to as Niemann-Pick disease type B (NPD-B). A phenotype with intermediate severity is also known as chronic neurovisceral ASMD (NPD-A/B). The most common presenting symptom in NPD-A is hepatosplenomegaly, usually detectable by age three months; over time the liver and spleen become massive in size. Psychomotor development progresses no further than the 12-month level, after which neurologic deterioration is relentless. Failure to thrive typically becomes evident by the second year of life. A classic cherry-red spot of the macula of the retina, which may not be present in the first few months, is eventually present in all affected children. Interstitial lung disease caused by storage of sphingomyelin in pulmonary macrophages results in frequent respiratory infections and often respiratory failure. Most children succumb before the third year of life. NPD-B generally presents later than NPD-A, and the manifestations are less severe. NPD-B is characterized by progressive hepatosplenomegaly, gradual deterioration in liver and pulmonary function, osteopenia, and atherogenic lipid profile. No central nervous system (CNS) manifestations occur. Individuals with NPD-A/B have symptoms that are intermediate between NPD-A and NPD-B. The presentation in individuals with NPD-A/B varies greatly, although all are characterized by the presence of some CNS manifestations. Survival to adulthood can occur in individuals with NPD-B and NPD-A/B.

Ornithine transcarbamylase (OTC) deficiency can occur as a severe neonatal-onset disease in males (but rarely in females) and as a post-neonatal-onset (also known as "late-onset" or partial deficiency) disease in males and females. Males with severe neonatal-onset OTC deficiency are asymptomatic at birth but become symptomatic from hyperammonemia in the first week of life, most often on day two to three of life, and are usually catastrophically ill by the time they come to medical attention. After successful treatment of neonatal hyperammonemic coma these infants can easily become hyperammonemic again despite appropriate treatment; they typically require liver transplant to improve quality of life. Males and heterozygous females with post-neonatal-onset (partial) OTC deficiency can present from infancy to later childhood, adolescence, or adulthood. No matter how mild the disease, a hyperammonemic crisis can be precipitated by stressors and become a life-threatening event at any age and in any situation in life. For all individuals with OTC deficiency, typical neuropsychological complications include developmental delay, learning disabilities, intellectual disability, attention-deficit/hyperactivity disorder, and executive function deficits.

Aldolase A deficiency is an autosomal recessive disorder associated with hereditary hemolytic anemia (Kishi et al., 1987).

Systemic primary carnitine deficiency (CDSP) is a disorder of the carnitine cycle that results in defective fatty acid oxidation. It encompasses a broad clinical spectrum including the following: Metabolic decompensation in infancy typically presenting between age three months and two years with episodes of hypoketotic hypoglycemia, poor feeding, irritability, lethargy, hepatomegaly, elevated liver transaminases, and hyperammonemia triggered by fasting or common illnesses such as upper respiratory tract infection or gastroenteritis. Childhood myopathy involving heart and skeletal muscle with onset between age two and four years. Pregnancy-related decreased stamina or exacerbation of cardiac arrhythmia. Fatigability in adulthood. Absence of symptoms. The latter two categories often include mothers diagnosed with CDSP after newborn screening has identified low carnitine levels in their infants.

McLeod neuroacanthocytosis syndrome (designated as MLS throughout this review) is a multisystem disorder with central nervous system (CNS), neuromuscular, cardiovascular, and hematologic manifestations in males: CNS manifestations are a neurodegenerative basal ganglia disease including movement disorders, cognitive alterations, and psychiatric symptoms. Neuromuscular manifestations include a (mostly subclinical) sensorimotor axonopathy and muscle weakness or atrophy of different degrees. Cardiac manifestations include dilated cardiomyopathy, atrial fibrillation, and tachyarrhythmia. Hematologically, MLS is defined as a specific blood group phenotype (named after the first proband, Hugh McLeod) that results from absent expression of the Kx erythrocyte antigen and weakened expression of Kell blood group antigens. The hematologic manifestations are red blood cell acanthocytosis and compensated hemolysis. Alloantibodies in the Kell and Kx blood group system can cause strong reactions to transfusions of incompatible blood and severe anemia in affected male newborns of Kell-negative mothers. Females heterozygous for XK pathogenic variants have mosaicism for the Kell and Kx blood group antigens. Although they usually lack CNS and neuromuscular manifestations, some heterozygous females may develop clinical manifestations including chorea or late-onset cognitive decline.

Carnitine palmitoyltransferase 1A (CPT1A) deficiency is a disorder of long-chain fatty acid oxidation. Clinical manifestations usually occur in an individual with a concurrent febrile or gastrointestinal illness when energy demands are increased; onset of symptoms is usually rapid. The recognized phenotypes are: acute fatty liver of pregnancy, in which the fetus has biallelic pathogenic variants in CPT1A that causes CPT1A deficiency; and hepatic encephalopathy, in which individuals (typically children) present with hypoketotic hypoglycemia and sudden onset of liver failure. Individuals with hepatic encephalopathy typically present with hypoglycemia, absent or low levels of ketones, and elevated serum concentrations of liver transaminases, ammonia, and total carnitine. Between episodes of hepatic encephalopathy, individuals appear developmentally and cognitively normal unless previous metabolic decompensation has resulted in neurologic damage.

Carnitine palmitoyltransferase II (CPT II) deficiency is a disorder of long-chain fatty-acid oxidation. The three clinical presentations are lethal neonatal form, severe infantile hepatocardiomuscular form, and myopathic form (which is usually mild and can manifest from infancy to adulthood). While the former two are severe multisystemic diseases characterized by liver failure with hypoketotic hypoglycemia, cardiomyopathy, seizures, and early death, the latter is characterized by exercise-induced muscle pain and weakness, sometimes associated with myoglobinuria. The myopathic form of CPT II deficiency is the most common disorder of lipid metabolism affecting skeletal muscle and the most frequent cause of hereditary myoglobinuria. Males are more likely to be affected than females.

Heme oxygenase-1 deficiency (HMOX1D) is a rare autosomal recessive disorder with a complex clinical presentation including direct antibody negative hemolytic anemia, low bilirubin, and hyperinflammation (summary by Chau et al., 2020). Other features may include asplenia and nephritis (Radhakrishnan et al., 2011).

Dent disease, an X-linked disorder of proximal renal tubular dysfunction, is characterized by low molecular weight (LMW) proteinuria, hypercalciuria, and at least one additional finding including nephrocalcinosis, nephrolithiasis, hematuria, hypophosphatemia, chronic kidney disease (CKD), and evidence of X-linked inheritance. Males younger than age ten years may manifest only LMW proteinuria and/or hypercalciuria, which are usually asymptomatic. Thirty to 80% of affected males develop end-stage renal disease (ESRD) between ages 30 and 50 years; in some instances ESRD does not develop until the sixth decade of life or later. The disease may also be accompanied by rickets or osteomalacia, growth restriction, and short stature. Disease severity can vary within the same family. Males with Dent disease 2 (caused by pathogenic variants in OCRL) may also have mild intellectual disability, cataracts, and/or elevated muscle enzymes. Due to random X-chromosome inactivation, some female carriers may manifest hypercalciuria and, rarely, renal calculi and moderate LMW proteinuria. Females rarely develop CKD.

Infantile-onset spinocerebellar ataxia (IOSCA) is a severe, progressive neurodegenerative disorder characterized by normal development until age one year, followed by onset of ataxia, muscle hypotonia, loss of deep-tendon reflexes, and athetosis. Ophthalmoplegia and sensorineural deafness develop by age seven years. By adolescence, affected individuals are profoundly deaf and no longer ambulatory; sensory axonal neuropathy, optic atrophy, autonomic nervous system dysfunction, and hypergonadotropic hypogonadism in females become evident. Epilepsy can develop into a serious and often fatal encephalopathy: myoclonic jerks or focal clonic seizures that progress to epilepsia partialis continua followed by status epilepticus with loss of consciousness.

MPV17-related mitochondrial DNA (mtDNA) maintenance defect presents in the vast majority of affected individuals as an early-onset encephalohepatopathic (hepatocerebral) disease that is typically associated with mtDNA depletion, particularly in the liver. A later-onset neuromyopathic disease characterized by myopathy and neuropathy, and associated with multiple mtDNA deletions in muscle, has also rarely been described. MPV17-related mtDNA maintenance defect, encephalohepatopathic form is characterized by: Hepatic manifestations (liver dysfunction that typically progresses to liver failure, cholestasis, hepatomegaly, and steatosis); Neurologic involvement (developmental delay, hypotonia, microcephaly, and motor and sensory peripheral neuropathy); Gastrointestinal manifestations (gastrointestinal dysmotility, feeding difficulties, and failure to thrive); and Metabolic derangements (lactic acidosis and hypoglycemia). Less frequent manifestations include renal tubulopathy, nephrocalcinosis, and hypoparathyroidism. Progressive liver disease often leads to death in infancy or early childhood. Hepatocellular carcinoma has been reported.

Citrin deficiency can manifest in newborns or infants as neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), in older children as failure to thrive and dyslipidemia caused by citrin deficiency (FTTDCD), and in adults as recurrent hyperammonemia with neuropsychiatric symptoms in citrullinemia type II (CTLN2). Often citrin deficiency is characterized by strong preference for protein-rich and/or lipid-rich foods and aversion to carbohydrate-rich foods. NICCD. Children younger than age one year have a history of low birth weight with growth restriction and transient intrahepatic cholestasis, hepatomegaly, diffuse fatty liver, and parenchymal cellular infiltration associated with hepatic fibrosis, variable liver dysfunction, hypoproteinemia, decreased coagulation factors, hemolytic anemia, and/or hypoglycemia. NICCD is generally not severe and symptoms often resolve by age one year with appropriate treatment, although liver transplantation has been required in rare instances. FTTDCD. Beyond age one year, many children with citrin deficiency develop a protein-rich and/or lipid-rich food preference and aversion to carbohydrate-rich foods. Clinical abnormalities may include growth restriction, hypoglycemia, pancreatitis, severe fatigue, anorexia, and impaired quality of life. Laboratory changes are dyslipidemia, increased lactate-to-pyruvate ratio, higher levels of urinary oxidative stress markers, and considerable deviation in tricarboxylic acid (TCA) cycle metabolites. One or more decades later, some individuals with NICCD or FTTDCD develop CTLN2. CTLN2. Presentation is sudden and usually between ages 20 and 50 years. Manifestations are recurrent hyperammonemia with neuropsychiatric symptoms including nocturnal delirium, aggression, irritability, hyperactivity, delusions, disorientation, restlessness, drowsiness, loss of memory, flapping tremor, convulsive seizures, and coma. Symptoms are often provoked by alcohol and sugar intake, medication, and/or surgery. Affected individuals may or may not have a prior history of NICCD or FTTDCD.

Mitochondrial HMG-CoA synthase deficiency (HMGCS2D) is an inherited metabolic disorder caused by a defect in the enzyme that regulates the formation of ketone bodies. Patients present with hypoketotic hypoglycemia, encephalopathy, and hepatomegaly, usually precipitated by an intercurrent infection or prolonged fasting (summary by Aledo et al., 2006).

Congenital disorder of glycosylation type It (CDG1T) is an autosomal recessive disorder characterized by a wide range of clinical manifestations and severity. The most common features include cleft lip and bifid uvula, apparent at birth, followed by hepatopathy, intermittent hypoglycemia, short stature, and exercise intolerance, often accompanied by increased serum creatine kinase. Less common features include rhabdomyolysis, dilated cardiomyopathy, and hypogonadotropic hypogonadism (summary by Tegtmeyer et al., 2014). For a discussion of the classification of CDGs, see CDG1A (212065).

The phenotypic spectrum of lysosomal acid lipase (LAL) deficiency ranges from the infantile-onset form (Wolman disease) to later-onset forms collectively known as cholesterol ester storage disease (CESD). Wolman disease is characterized by infantile-onset malabsorption that results in malnutrition, storage of cholesterol esters and triglycerides in hepatic macrophages that results in hepatomegaly and liver disease, and adrenal gland calcification that results in adrenal cortical insufficiency. Unless successfully treated with hematopoietic stem cell transplantation (HSCT), infants with classic Wolman disease do not survive beyond age one year. CESD may present in childhood in a manner similar to Wolman disease or later in life with such findings as serum lipid abnormalities, hepatosplenomegaly, and/or elevated liver enzymes long before a diagnosis is made. The morbidity of late-onset CESD results from atherosclerosis (coronary artery disease, stroke), liver disease (e.g., altered liver function ± jaundice, steatosis, fibrosis, cirrhosis and related complications of esophageal varices, and/or liver failure), complications of secondary hypersplenism (i.e., anemia and/or thrombocytopenia), and/or malabsorption. Individuals with CESD may have a normal life span depending on the severity of disease manifestations.

Immunodeficiency-90 with encephalopathy, functional hyposplenia, and hepatic dysfunction (IMD90) is a autosomal recessive complex immunologic disorder with systemic manifestations in addition to primary immunodeficiency. Affected individuals usually present in infancy or early childhood with recurrent fevers and bacterial or viral infections associated with central nervous system symptoms, including irritability, drowsiness, variable seizures, and white matter abnormalities on brain imaging. There is also liver involvement and functional hyposplenism, causing increased susceptibility to invasive pneumococcal infection, which may be fatal. Susceptibility to viral infections likely results from impaired interferon immunity, and bacterial infections likely result from splenic dysfunction. A subset of patients have congenital cardiac malformations. Most individuals demonstrate developmental delay and speech delay. Laboratory findings in affected individuals are similar to those seen in autoimmune lymphoproliferative syndrome (ALPS; 601859), including high-circulating CD4-/CD8-/TCR-alpha-beta+ (double-negative) T-cell (DNT) counts, and elevated IL10 (124092) and FASL (TNFSF6; 134638) levels, but the clinical features are somewhat different from ALPS: massive lymphadenopathy and autoimmune features are not observed in IMD90 (summary by Bolze et al., 2010, Savic et al., 2015 and Kohn et al., 2020).

Congenital bile acid synthesis defect-3 (CBAS3) is an autosomal recessive disorder characterized by prolonged jaundice after birth, hepatomegaly, conjugated hyperbilirubinemia, elevations in characteristic abnormal bile acids, and progressive intrahepatic cholestasis with liver fibrosis (summary by Setchell et al., 1998 and Ueki et al., 2008). For a general phenotypic description and a discussion of genetic heterogeneity of congenital bile acid synthesis defects, see 607765.

SUCLG1-related mitochondrial DNA (mtDNA) depletion syndrome, encephalomyopathic form with methylmalonic aciduria is characterized in the majority of affected newborns by hypotonia, muscle atrophy, feeding difficulties, and lactic acidosis. Affected infants commonly manifest developmental delay / cognitive impairment, growth retardation / failure to thrive, hepatopathy, sensorineural hearing impairment, dystonia, and hypertonia. Notable findings in some affected individuals include hypertrophic cardiomyopathy, epilepsy, myoclonus, microcephaly, sleep disturbance, rhabdomyolysis, contractures, hypothermia, and/or hypoglycemia. Life span is shortened, with median survival of 20 months.

Acute infantile liver failure resulting from TRMU mutation is a transient disorder of hepatic function. In addition to elevated liver enzymes, jaundice, vomiting, coagulopathy, and hyperbilirubinemia, the presence of increased serum lactate is consistent with a defect in mitochondrial respiratory function. With supportive care, patients who survive the initial acute episode can recover and show normal development (Zeharia et al., 2009). See also transient infantile mitochondrial myopathy (MMIT; 500009), which is a similar disorder. A more severe, permanent disorder with some overlapping features is associated with mitochondrial DNA depletion (251880). See ILFS1 (615438) for information on syndromic infantile liver failure.

CDG2K is an autosomal recessive disorder with a variable phenotype. Affected individuals show psychomotor retardation and growth retardation, and most have short stature. Other features include dysmorphism, hypotonia, eye abnormalities, acquired microcephaly, hepatomegaly, and skeletal dysplasia. Serum transferrin analysis shows a CDG type II pattern (summary by Foulquier et al., 2012). For a general discussion of CDGs, see CDG1A (212065) and CDG2A (212066).

Combined oxidative phosphorylation deficiency-16 (COXPD16) is an autosomal recessive multisystem disorder with hypertrophic cardiomyopathy as a major feature.

Autoimmune lymphoproliferative syndrome type III is an autosomal recessive disorder of immune dysregulation. The phenotype is variable, but most patients have significant lymphadenopathy associated with variable autoimmune manifestations. Some patients may have recurrent infections. Lymphocyte accumulation results from a combination of impaired apoptosis and excessive proliferation (summary by Oliveira, 2013). For a general description and a discussion of genetic heterogeneity of ALPS, see 601859.

Any combined oxidative phosphorylation deficiency in which the cause of the disease is a mutation in the LYRM4 gene.

Immunodeficiency-44 (IMD44) is an autosomal recessive primary immunodeficiency characterized by increased susceptibility to viral infections and adverse multisystemic reaction to vaccination in some patients. Affected individuals appear to have defects in mitochondrial fission and fusion (summary by Shahni et al., 2015).

Immunodeficiency-40 is an autosomal recessive primary form of combined immunodeficiency mainly affecting T-cell number and function, with other more variable defects in B-cell and NK-cell function. Patients have onset of severe invasive bacterial and viral infections in early childhood and may die without bone marrow transplantation (summary by Dobbs et al., 2015).

Interstitial lung and liver disease is an autosomal recessive disorder characterized by onset of respiratory insufficiency and progressive liver disease in infancy or early childhood. Pathologic examination of lung lavage is consistent with pulmonary alveolar proteinosis (summary by Hadchouel et al., 2015).

Any congenital bile acid synthesis defect in which the cause of the disease is a mutation in the ACOX2 gene.

Any Seckel syndrome in which the cause of the disease is a mutation in the NSMCE2 gene.

Progressive familial intrahepatic cholestasis-5 (PFIC5) is an autosomal recessive severe liver disorder characterized by onset of intralobular cholestasis in the neonatal period. The disease is rapidly progressive, leading to liver failure and death if liver transplant is not performed. Other features include abnormal liver enzymes, low to normal gamma-glutamyl transferase (GGT) activity, increased alpha-fetoprotein, and a vitamin K-independent coagulopathy (summary by Gomez-Ospina et al., 2016). For a general phenotypic description and a discussion of genetic heterogeneity of PFIC, see PFIC1 (211600).

Immunodeficiency-47 (IMD47) is an X-linked recessive complex syndrome characterized by liver dysfunction, recurrent bacterial infections, hypogammaglobulinemia, and defective glycosylation of serum proteins. Some patients also have neurologic abnormalities (summary by Jansen et al., 2016).

Individuals with biallelic APOB-related familial hypobetalipoproteinemia (APOB-FHBL) may present from infancy through to adulthood with a range of clinical symptoms including deficiency of fat-soluble vitamins and gastrointestinal and neurologic dysfunction. Affected individuals typically have plasma total cholesterol, LDL cholesterol, and apo B levels below the fifth centile for age and sex. Acanthocytosis, elevated liver enzymes, and hyperbilirubinemia may also be found. The most common clinical findings are hepatomegaly, steatorrhea, and failure to thrive / growth deficiency. In the absence of treatment, affected individuals can develop atypical pigmentation of the retina; progressive loss of deep tendon reflexes, vibratory sense, and proprioception; muscle pain or weakness; dysarthria; ataxia; tremors; and steatohepatitis, fibrosis, and rarely, cirrhosis of the liver. Individuals with a heterozygous, typically truncating pathogenic variant in APOB are usually asymptomatic with mild liver dysfunction and hepatic steatosis. However, about 5%-10% of individuals with heterozygous APOB-FHBL develop relatively more severe nonalcoholic steatohepatitis requiring medical attention and occasionally progressing to cirrhosis, albeit very rarely.

A rare mitochondrial disease due to a defect in mitochondrial protein synthesis characterized by initially normal growth and development followed by the infantile-onset of failure to thrive, psychomotor delay, poor feeding, dyspnea, severe hypertrophic cardiomyopathy and hepatomegaly. Laboratory studies report increased plasma lactate and alanine, abnormal liver enzymes and decreased activity of mitochondrial respiratory chain complexes I, III, IV, and V. Caused by compound heterozygous mutation in the MRPL3 gene on chromosome 3q22.

Hypermethioninemia due to adenosine kinase deficiency is an autosomal recessive inborn error of metabolism characterized by global developmental delay, early-onset seizures, mild dysmorphic features, and characteristic biochemical anomalies, including persistent hypermethioninemia with increased levels of S-adenosylmethionine (AdoMet) and S-adenosylhomocysteine (AdoHcy); homocysteine is typically normal (summary by Bjursell et al., 2011).

Triokinase and FMN cyclase deficiency syndrome (TKFCD) is a multisystem disease with marked clinical variability, even intrafamilially. In addition to cataract and developmental delay of variable severity, other features may include liver dysfunction, microcytic anemia, and cerebellar hypoplasia. Fatal cardiomyopathy with lactic acidosis has been observed (Wortmann et al., 2020).

Hypervalinemia and hyperleucine-isoleucinemia (HVLI) is a branched-chain amino acid metabolic disorder characterized by highly elevated plasma valine and leucine concentrations. The patient presented in adulthood with headache and mild memory impairment, and had abnormal symmetric white matter signals on brain MRI (Wang et al., 2015).

Mitochondrial complex IV deficiency nuclear type 4 (MC4DN4) is an autosomal recessive multisystem metabolic disorder characterized by the onset of symptoms in infancy. Affected individuals show hypotonia, failure to thrive, and neurologic distress. Additional features include hepatomegaly, hepatic steatosis, increased serum lactate, and metabolic acidosis. Some patients may develop hypertrophic cardiomyopathy. Patient tissues show decreased levels and activity of mitochondrial respiratory complex IV. Death usually occurs in infancy (summary by Valnot et al., 2000 and Stiburek et al., 2009). For a discussion of genetic heterogeneity of mitochondrial complex IV (cytochrome c oxidase) deficiency, see 220110.

Bile acid conjugation defect-1 (BACD1) is an autosomal recessive metabolic disorder characterized by onset of symptoms, including jaundice and failure to thrive, in early infancy. The clinical features of the disorder result from impaired absorption of fat-soluble vitamins. Vitamin D deficiency causes rickets with variable growth deficiency, and vitamin K deficiency causes a coagulopathy with decreased production of vitamin K-dependent clotting factors. More variable features may include pruritis, anemia, hepatomegaly, and bile duct proliferation on liver biopsy. Laboratory studies show abnormally increased levels of unconjugated bile acids (summary by Setchell et al., 2013). See also familial hypercholanemia (FHCA; 607748), in which patients have increased serum bile levels of conjugated bile acids.

Combined oxidative phosphorylation deficiency-52 (COXPD52) is an autosomal recessive infantile mitochondrial complex II/III deficiency characterized by lactic acidemia, multiorgan system failure, and abnormal mitochondria. Intrafamilial variability has been reported (Farhan et al., 2014; Hershkovitz et al., 2021). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

Primary bile acid malabsorption-2 (PBAM2) is an autosomal recessive disorder characterized by chronic diarrhea, severe fat-soluble vitamin deficiency, and features of cholestatic liver disease (Sultan et al., 2018). For discussion of genetic heterogeneity of primary bile acid malabsorption, see PBAM1 (613291).

Congenital disorder of glycosylation type IIw (CDG2W) is an autosomal dominant metabolic disorder characterized by liver dysfunction, coagulation deficiencies, and profound abnormalities in N-glycosylation of serum specific proteins. All reported patients carry the same mutation (602671.0017) (summary by Ng et al., 2021). For an overview of congenital disorders of glycosylation, see CDG1A (212065) and CDG2A (212066).

Biliary, renal, neurologic, and skeletal syndrome (BRENS) is an autosomal recessive complex ciliopathy with multisystemic manifestations. The most common presentation is severe neonatal cholestasis that progresses to liver fibrosis and cirrhosis. Most patients have additional clinical features suggestive of a ciliopathy, including postaxial polydactyly, hydrocephalus, retinal abnormalities, and situs inversus. Additional features of the syndrome may include congenital cardiac defects, echogenic kidneys with renal failure, ocular abnormalities, joint hyperextensibility, and dysmorphic facial features. Some patients have global developmental delay. Brain imaging typically shows dilated ventricles, hypomyelination, and white matter abnormalities, although some patients have been described with abnormal pituitary development (summary by Shaheen et al., 2020 and David et al., 2020).

Progressive intrahepatic cholestasis-7 with or without hearing loss (PFIC7) is an autosomal recessive liver disorder characterized by infantile-onset jaundice and itching associated with cholestasis, elevated alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and normal gamma glutamyltransferase (GGT). Liver biopsy shows hepatocellular and canalicular cholestasis with fibrotic changes. Many patients have resolution of the liver abnormalities with age, although some may have persistent liver enzyme abnormalities or splenomegaly. A subset of patients develops hearing loss in childhood between early infancy and the teenage years. Rifampicin may be effective for pruritis (summary by Maddirevula et al., 2019). For a discussion of genetic heterogeneity of PFIC, see PFIC1 (211600).

Progressive familial intrahepatic cholestasis-8 (PFIC8) is an autosomal recessive disorder characterized by cholestasis and high gamma-glutamyltransferase presenting in the infantile period (summary by Unlusoy Aksu et al., 2019). For a general phenotypic description and a discussion of genetic heterogeneity of PFIC, see PFIC1 (211600).

Neurodevelopmental disorder with microcephaly, seizures, and neonatal cholestasis (NEDMSC) is an autosomal recessive disorder characterized by severely impaired global development apparent from infancy, progressive microcephaly, and neonatal cholestasis manifest as jaundice and elevated liver enzymes. The liver disease resolves, but affected individuals show feeding difficulties, failure to thrive, hypotonia, seizures, hyperkinetic movements, irritability, and poor eye contact or vision, and achieve almost no motor or cognitive developmental milestones. Brain imaging demonstrates agenesis or hypoplasia of the corpus callosum. Death in early childhood may occur (summary by Schneeberger et al., 2021).

Immunodeficiency-87 and autoimmunity (IMD87) is an autosomal recessive immunologic disorder with wide phenotypic variation and severity. Affected individuals usually present in infancy or early childhood with increased susceptibility to infections, often Epstein-Barr virus (EBV), as well as with lymphadenopathy or autoimmune manifestations, predominantly hemolytic anemia. Laboratory studies may show low or normal lymphocyte numbers, often with skewed T-cell subset ratios. The disorder results primarily from defects in T-cell function, which causes both immunodeficiency and overall immune dysregulation (summary by Serwas et al., 2019 and Fournier et al., 2021).

Cytosolic phosphoenolpyruvate carboxykinase deficiency causes a defect in gluconeogenesis that results in a 'biochemical signature' of fasting hypoglycemia with high tricarboxylic acid cycle intermediate excretion, particularly of fumarate. Other biochemical anomalies that may be seen during metabolic crisis include ketonuria, dicarboxylic aciduria, and urea cycle dysfunction (Vieira et al., 2017). See PCKDM (261650) for a discussion of mitochondrial PCK (PEPCK2; 614095) deficiency.

Progressive familial intrahepatic cholestasis-10 (PFIC10) is an autosomal recessive liver disorder characterized by the onset of symptoms in the first months or years of life. Features include jaundice, pruritis, and hepatomegaly associated with increased serum bilirubin and bile acids. Liver transaminases may be variably increased, but gamma-glutamyltransferase (GGT; see 612346) is normal. Liver biopsy shows hepatocellular and canalicular cholestasis with giant cell changes. Although rare patients may have episodes of diarrhea and even show endoscopic features of microvillus inclusion disease (MVID), this tends to be transient and cholestasis dominates the clinical picture (Gonzales et al., 2017; Cockar et al., 2020). For a discussion of genetic heterogeneity of progressive familial intrahepatic cholestasis, see PFIC1 (211600).