TYK2 and Mendelian susceptibility to mycobacterial diseases: Molecular confirmation through whole-exome sequencing identified two rare TYK2 variants, comprising a truncating loss-of-function allele and the p.Gly799Arg substitution, which has been previously reported in a Chinese patient and functionally validated as pathogenic in TYK2 deficiency [18], strongly supporting TYK2-related MSMD in this child.