MedGen

Genetic defects in the pyruvate dehydrogenase complex are one of the most common causes of primary lactic acidosis in children. Most cases are caused by mutation in the E1-alpha subunit gene on the X chromosome. X-linked PDH deficiency is one of the few X-linked diseases in which a high proportion of heterozygous females manifest severe symptoms. The clinical spectrum of PDH deficiency is broad, ranging from fatal lactic acidosis in the newborn to chronic neurologic dysfunction with structural abnormalities in the central nervous system without systemic acidosis (Robinson et al., 1987; Brown et al., 1994). Genetic Heterogeneity of Pyruvate Dehydrogenase Complex Deficiency PDH deficiency can also be caused by mutation in other subunits of the PDH complex, including a form (PDHXD; 245349) caused by mutation in the component X gene (PDHX; 608769) on chromosome 11p13; a form (PDHBD; 614111) caused by mutation in the PDHB gene (179060) on chromosome 3p14; a form (PDHDD; 245348) caused by mutation in the DLAT gene (608770) on chromosome 11q23; a form (PDHPD; 608782) caused by mutation in the PDP1 gene (605993) on chromosome 8q22; and a form (PDHLD; 614462) caused by mutation in the LIAS gene (607031) on chromosome 4p14. [from OMIM]

Pyruvate carboxylase (PC) deficiency is characterized in most affected individuals by failure to thrive, developmental delay, recurrent seizures, and metabolic acidosis. Three clinical types are recognized: Type A (infantile form), in which most affected children die in infancy or early childhood. Type B (severe neonatal form), in which affected infants have hepatomegaly, pyramidal tract signs, and abnormal movement and die within the first three months of life. Type C (intermittent/benign form), in which affected individuals have normal or mildly delayed neurologic development and episodic metabolic acidosis. [from GeneReviews]

N-acetylglutamate synthase deficiency is an autosomal recessive disorder of the urea cycle. The clinical and biochemical features of the disorder are indistinguishable from carbamoyl phosphate synthase I deficiency (237300), since the CPS1 enzyme (608307) has an absolute requirement for NAGS (Caldovic et al., 2007). [from OMIM]

Pyruvate dehydrogenase deficiency is characterized by the buildup of a chemical called lactic acid in the body and a variety of neurological problems. Signs and symptoms of this condition usually first appear shortly after birth, and they can vary widely among affected individuals. The most common feature is a potentially life-threatening buildup of lactic acid (lactic acidosis), which can cause nausea, vomiting, severe breathing problems, and an abnormal heartbeat. People with pyruvate dehydrogenase deficiency usually have neurological problems as well. Most have delayed development of mental abilities and motor skills such as sitting and walking. Other neurological problems can include intellectual disability, seizures, weak muscle tone (hypotonia), poor coordination, and difficulty walking. Some affected individuals have abnormal brain structures, such as underdevelopment of the tissue connecting the left and right halves of the brain (corpus callosum), wasting away (atrophy) of the exterior part of the brain known as the cerebral cortex, or patches of damaged tissue (lesions) on some parts of the brain. Because of the severe health effects, many individuals with pyruvate dehydrogenase deficiency do not survive past childhood, although some may live into adolescence or adulthood. [from MedlinePlus Genetics]

FBXL4-related encephalomyopathic mitochondrial DNA (mtDNA) depletion syndrome is a multi-system disorder characterized primarily by congenital or early-onset lactic acidosis and growth failure, feeding difficulty, hypotonia, and developmental delay. Other neurologic manifestations can include seizures, movement disorders, ataxia, autonomic dysfunction, and stroke-like episodes. All affected individuals alive at the time they were reported (median age: 3.5 years) demonstrated significant developmental delay. Other findings can involve the heart (hypertrophic cardiomyopathy, congenital heart malformations, arrhythmias), liver (mildly elevated transaminases), eyes (cataract, strabismus, nystagmus, optic atrophy), hearing (sensorineural hearing loss), and bone marrow (neutropenia, lymphopenia). Survival varies; the median age of reported deaths was two years (range 2 days – 75 months), although surviving individuals as old as 36 years have been reported. To date FBXL4-related mtDNA depletion syndrome has been reported in 50 individuals. [from GeneReviews]

The phenotypic spectrum of SERAC1 deficiency comprises MEGD(H)EL syndrome (3-methylglutaconic aciduria with deafness-dystonia, [hepatopathy], encephalopathy, and Leigh-like syndrome), juvenile-onset complicated hereditary spastic paraplegia (in 1 consanguineous family), and adult-onset generalized dystonia (in 1 adult male). MEGD(H)EL syndrome is characterized in neonates by hypoglycemia and a sepsis-like clinical picture for which no infectious agent can be found. During the first year of life feeding problems, failure to thrive, and/or truncal hypotonia become evident; many infants experience (transient) liver involvement ranging from undulating transaminases to prolonged hyperbilirubinemia and near-fatal liver failure. By age two years progressive deafness, dystonia, and spasticity prevent further psychomotor development and/or result in loss of acquired skills. Affected children are completely dependent on care for all activities of daily living; speech is absent. [from GeneReviews]

Mitochondrial DNA depletion syndrome-12B is an autosomal recessive mitochondrial disorder characterized by childhood onset of slowly progressive hypertrophic cardiomyopathy and generalized skeletal myopathy resulting in exercise intolerance, and, in some patients, muscle weakness and atrophy. Skeletal muscle biopsy shows ragged-red fibers, mtDNA depletion, and accumulation of abnormal mitochondria (summary by Echaniz-Laguna et al., 2012). For a discussion of genetic heterogeneity of mtDNA depletion syndromes, see MTDPS1 (603041). [from OMIM]

Mitochondrial encephalo-cardio-myopathy due to <i>TMEM70</i> mutation is characterized by early neonatal onset of hypotonia, hypetrophic cardiomyopathy and apneic spells within hours after birth accompanied by lactic acidosis, hyperammonemia and 3-methylglutaconic aciduria. [from ORDO]

Primary coenzyme Q10 (CoQ10) deficiency is usually associated with multisystem involvement, including neurologic manifestations such as fatal neonatal encephalopathy with hypotonia; a late-onset slowly progressive multiple-system atrophy-like phenotype (neurodegeneration with autonomic failure and various combinations of parkinsonism and cerebellar ataxia, and pyramidal dysfunction); and dystonia, spasticity, seizures, and intellectual disability. Steroid-resistant nephrotic syndrome (SRNS), the hallmark renal manifestation, is often the initial manifestation either as isolated renal involvement that progresses to end-stage renal disease (ESRD), or associated with encephalopathy (seizures, stroke-like episodes, severe neurologic impairment) resulting in early death. Hypertrophic cardiomyopathy (HCM), retinopathy or optic atrophy, and sensorineural hearing loss can also be seen. [from GeneReviews]

Encephalopathy due to defective mitochondrial and peroxisomal fission-1 (EMPF1) is characterized by delayed psychomotor development and hypotonia that may lead to death in childhood. Many patients develop refractory seizures, consistent with an epileptic encephalopathy, and thereafter show neurologic decline. The age at onset, features, and severity are variable, and some patients may not have clinical evidence of mitochondrial or peroxisomal dysfunction (summary by Sheffer et al., 2016; Fahrner et al., 2016). Genetic Heterogeneity of Encephalopathy Due to Defective Mitochondrial And Peroxisomal Fission See also EMPF2 (617086), caused by mutation in the MFF gene (614785) on chromosome 2q36. [from OMIM]

Isolated complex I deficiency is a rare inborn error of metabolism due to mutations in nuclear or mitochondrial genes encoding subunits or assembly factors of the human mitochondrial complex I (NADH: ubiquinone oxidoreductase) and is characterized by a wide range of manifestations including marked and often fatal lactic acidosis, cardiomyopathy, leukoencephalopathy, pure myopathy and hepatopathy with tubulopathy. Among the numerous clinical phenotypes observed are Leigh syndrome, Leber hereditary optic neuropathy and MELAS syndrome (see these terms). [from ORDO]

Combined oxidative phosphorylation deficiency-10 (COXPD10) is an autosomal recessive disorder resulting in variable defects of mitochondrial oxidative respiration. Affected individuals present in infancy with hypertrophic cardiomyopathy and lactic acidosis. The severity is variable, but can be fatal in the most severe cases (summary by Ghezzi et al., 2012). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060). [from OMIM]

Any mitochondrial DNA depletion syndrome in which the cause of the disease is a mutation in the OPA1 gene. [from MONDO]

Individuals with NGLY1-related congenital disorder of deglycosylation (NGLY1-CDDG) typically display a clinical tetrad of developmental delay / intellectual disability in the mild to profound range, hypo- or alacrima, elevated liver transaminases that may spontaneously resolve in childhood, and a complex hyperkinetic movement disorder that can include choreiform, athetoid, dystonic, myoclonic, action tremor, and dysmetric movements. About half of affected individuals will develop clinical seizures. Other findings may include obstructive and/or central sleep apnea, oral motor defects that affect feeding ability, auditory neuropathy, constipation, scoliosis, and peripheral neuropathy. [from GeneReviews]

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. [from SNOMEDCT_US]

Most children with carbonic anhydrase VA (CA-VA) deficiency reported to date have presented between day 2 of life and early childhood (up to age 20 months) with hyperammonemic encephalopathy (i.e., lethargy, feeding intolerance, weight loss, tachypnea, seizures, and coma). Given that fewer than 20 affected individuals have been reported to date, the ranges of initial presentations and long-term prognoses are not completely understood. As of 2021 the oldest known affected individual is an adolescent. Almost all affected individuals reported to date have shown normal psychomotor development and no further episodes of metabolic crisis; however, a few have shown mild learning difficulties or delayed motor skills. [from GeneReviews]

Combined oxidative phosphorylation defect type 20 is a rare mitochondrial oxidative phosphorylation disorder characterized by variable combination of psychomotor delay, hypotonia, muscle weakness, seizures, microcephaly, cardiomyopathy and mild dysmorphic facial features. Variable types of structural brain anomalies have also been reported. Biochemical studies typically show decreased activity of mitochondrial complexes (mainly complex I). [from ORDO]

Combined oxidative phosphorylation deficiency-21 (COXPD21) is an autosomal recessive disorder characterized either by onset within the first months of life of severe hypotonia, failure to thrive, epilepsy and early death or by onset after 6 months of life with a milder course and longer survival (summary by Zheng et al., 2022). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060). [from OMIM]

A rare mitochondrial oxidative phosphorylation disorder with characteristics of neonatal onset of hypotonia, feeding difficulties, deafness, and early fatal respiratory failure. Cardiac and liver involvement has been reported. Serum lactate is increased and metabolic studies show decreased activity of mitochondrial respiratory complexes I and IV in skeletal muscle. [from SNOMEDCT_US]