Severe combined immunodeficiency due to FOXN1 deficiency

Severe combined immunodeficiency (SCID) due to FOXN1 deficiency, also known as Nude SCID or Nude/SCID syndrome, is an extremely rare autosomal recessive disorder caused by loss-of-function mutations in the FOXN1 gene (also known as WHN). This gene encodes a transcription factor essential for the development of the thymus and for proper differentiation of epithelial cells in the skin, hair, and nails. Without functional FOXN1, the thymus fails to develop normally (thymic aplasia or severe hypoplasia), resulting in a profound T-cell immunodeficiency. The condition is the human equivalent of the nude mouse phenotype. Affected infants present at birth or in early infancy with the classic triad of congenital alopecia (absence of hair, including eyebrows and eyelashes), nail dystrophy, and severe T-cell immunodeficiency. The absence of functional T cells leads to extreme susceptibility to severe, recurrent, and life-threatening infections including bacterial, viral, and fungal pathogens, as well as opportunistic organisms. B-cell numbers may be normal but their function is impaired due to the lack of T-cell help. The condition is typically fatal in early childhood without definitive treatment. The primary curative treatment is hematopoietic stem cell transplantation (HSCT), although thymus transplantation has also been explored as a more targeted therapeutic approach, since the fundamental defect lies in the thymic epithelium rather than in the hematopoietic stem cells themselves. Thymus transplantation has shown promising results in restoring T-cell immunity in affected patients. Supportive care includes infection prophylaxis, immunoglobulin replacement therapy, and protective isolation. Early diagnosis and prompt intervention are critical for survival.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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