A rare genetic disorder with an autosomal recessive pattern of inheritance. It is caused by the ineffective or decreased biosynthesis of the fifth complement component, C5. C5 deficiency may also be acquired acutely post-infection. If C5 is adequately synthesized, its rapid depletion may result in a functional deficiency. Clinical signs of the inherited deficiency present within the second decade of life and are consistent with the signs of recurrent systemic infection. Deficiency of serum C5 and its major cleavage product, C5b, a component of the membrane attack complex, increases susceptibility to Neisserial infections.

Congenital tufting enteropathy (CTE) is a rare inherited intractable diarrhea of infancy characterized by villous atrophy and absence of inflammation, with intestinal epithelial cell dysplasia manifesting as focal epithelial tufts in the duodenum and jejunum. CTE presents in the first few months of life with chronic watery diarrhea and failure to thrive, and most affected individuals require parenteral nutrition for normal growth and development (summary by Sivagnanam et al., 2008). Semiquantitative assessment of the epithelial surface in CTE patients revealed that 80 to 90% contained tufts, compared to only 16% in patients with celiac disease and less than 10% in normal jejunum (Reifen et al., 1994). For a discussion of genetic heterogeneity of diarrhea, see DIAR1 (214700).

Specific granule deficiency-2 (SGD2) is an autosomal recessive immunologic disorder characterized by recurrent infections due to defective neutrophil development. Bone marrow findings include paucity of neutrophil granulocytes, absence of granule proteins in neutrophils, abnormal megakaryocytes, and features of progressive myelofibrosis with blasts. The disorder is apparent from infancy, and patients may die in early childhood unless they undergo hematopoietic stem cell transplantation. Most patients have additional findings, including delayed development, mild dysmorphic features, tooth abnormalities, and distal skeletal defects (Witzel et al., 2017). For a discussion of genetic heterogeneity of SGD, see SGD1 (245480).

Trichohepatoenteric syndrome (THES), generally considered to be a neonatal enteropathy, is characterized by intractable diarrhea (seen in almost all affected children), woolly hair (seen in all), intrauterine growth restriction, facial dysmorphism, and short stature. Additional findings include poorly characterized immunodeficiency, recurrent infections, skin abnormalities, and liver disease. Mild intellectual disability (ID) is seen in about 50% of affected individuals. Less common findings include congenital heart defects and platelet anomalies. To date 52 affected individuals have been reported.

Immunodeficiency-82 with systemic inflammation (IMD82) is a complex autosomal dominant immunologic disorder characterized by recurrent infections with various organisms, as well as noninfectious inflammation manifest as lymphocytic organ infiltration with gastritis, colitis, and lung, liver, CNS, or skin disease. One of the more common features is inflammation of the stomach and bowel. Most patients develop symptoms in infancy or early childhood; the severity is variable. There may be accompanying fever, elevated white blood cell count, decreased B cells, hypogammaglobulinemia, increased C-reactive protein (CRP; 123260), and a generalized hyperinflammatory state. Immunologic workup shows variable B- and T-cell abnormalities such as skewed subgroups. Patients have a propensity for the development of lymphoma, usually in adulthood. At the molecular level, the disorder results from a gain-of-function mutation that leads to constitutive and enhanced activation of the intracellular inflammatory signaling pathway. Treatment with SYK inhibitors rescued human cell abnormalities and resulted in clinical improvement in mice (Wang et al., 2021).

Epidermolysis bullosa with pyloric atresia (EB-PA) is characterized by fragility of the skin and mucous membranes, manifested by blistering with little or no trauma; congenital pyloric atresia; and ureteral and renal anomalies (dysplastic/multicystic kidney, hydronephrosis/hydroureter, ureterocele, duplicated renal collecting system, absent bladder). The course of EB-PA is usually severe and often lethal in the neonatal period. Most affected children succumb as neonates; those who survive may have severe blistering with formation of granulation tissue on the skin around the mouth, nose, fingers, and toes, and internally around the trachea. However, some affected individuals have little or no blistering later in life. Additional features shared by EB-PA and the other major forms of EB include congenital localized absence of skin (aplasia cutis congenita) affecting the extremities and/or head, milia, nail dystrophy, scarring alopecia, hypotrichosis, contractures, and dilated cardiomyopathy.