Objective  To analyze the clinical and immunological characteristics of the first case of FOXN1 haploinsufficiency in China and summarize the clinical characteristics of previous reported cases in other countries.

  Methods  The whole-exome sequencing(WES) and Sanger sequencing were conducted to verify the mutation of FOXN1.The T cell receptor rearrangement excision circles(TRECs)and κ-deleting recombination excision circles(κRECs)copies, peripheral blood lymphocyte subsets and T cell receptor (TCR) Vβ repertoire were further detected。A literature search was conducted using PubMed, Wangfang Med Online and CNKI with search terms "FOXN1 deficiency" and "FOXN1 haploinsufficiency".

  Results  A 1-year-old girl manifested with recurrent autoimmune hemolytic anemia, hair loss and nail dystrophy. Genetic mutation of FOXN1 (c.1392_1401delTCCTGGACCC, p.P465Rfs*82) was confirmed by WES and Sanger sequencing. The TRECs were 0.35 copies/μL, κRECs were normal. The TCR Vβ repertoire in this patient was markedly oligoclonal. Lymphocytes subsets revealed a predominate decrease of CD4⁺ T cell and Naïve CD4⁺ T, and an increase of effector memory helper T cells. A total of 5 publications were included (5 English and 0 Chinese). Thus far, 41 cases have been reported worldwide who mostly manifested with the decrease of T cells in early childhood.

  Conclusions  FOXN1 haploinsufficiency deficiency is a kind of combined immunodeficiency disease, which is mainly manifested by the decrease of T cells and repeated infection in infants and young children, and may also be accompanied by hair loss, nail dystrophy and autoimmune disease, which cannot be cured by hematopoietic stem cell transplantation.