PAX1 and congenital T-cell immunodeficiency: In addition, biallelic PAX1 (paired box 1) variants underlie OTFCS type 2 with T-cell deficiency (OTFCS2) [19,20,21,22], while loss-of-function (LoF) variants in EYA4 (EYA transcriptional coactivator and phosphatase 4) have more recently been reported in a single affected family [4].