Diarrhea-2 with microvillus atrophy, with or without cholestasis (DIAR2) is characterized by onset of intractable life-threatening watery diarrhea during infancy. Two forms are recognized: early-onset microvillus inclusion disease (MVID) with diarrhea beginning in the neonatal period, and late-onset, with first symptoms appearing after 3 or 4 months of life. Definite diagnosis is made by transmission electron microscopy demonstrating shortening or absence of apical microvilli with pathognomonic microvillus inclusions in mature enterocytes and peripheral accumulation of periodic acid-Schiff (PAS)-positive granules or vesicles in immature enterocytes (Muller et al., 2008). The natural course of MVID is often fatal, but partial or total weaning from parenteral nutrition has been described. For a discussion of genetic heterogeneity of diarrhea, see DIAR1 (214700).

Any severe combined immunodeficiency in which the cause of the disease is a mutation in the CD247 gene.

A rare autosomal recessive primary immunodeficiency characterized by absence of HLA class II molecules on the surface of immune cells, leading to severely impaired cellular and humoral immune response to foreign antigens, severe CD4+ T-cell lymphopenia, and hypogammaglobulinemia. The disease clinically manifests with early onset of severe and recurrent infections mainly of the respiratory and gastrointestinal tract, protracted diarrhea with failure to thrive, and autoimmune disease, and is frequently fatal in childhood.

Immunodeficiency-22 (IMD22) is an autosomal recessive disorder characterized by the onset of recurrent bacterial, viral, and fungal respiratory, gastrointestinal, and skin infections in infancy or early childhood. Immunologic workup shows severe T-cell lymphopenia, particularly affecting the CD4+ subset, and impaired proximal TCR intracellular signaling and activation. Although NK cells and B cells are normal, some patients may have hypogammaglobulinemia secondary to the T-cell defect. There are variable manifestations, likely due to the severity of the particular LCK mutation: patients may develop prominent skin lesions resembling epidermodysplasia verruciformis, gastrointestinal inflammation, and virus-induced malignancy. The disease can be fatal in childhood, but hematopoietic stem cell transplant (HSCT) may be curative (Hauck et al., 2012; Li et al., 2016; Keller et al., 2023).