The c.1333C>T (p.Arg445Ter) (NM_000215.4) variant in JAK3 is a nonsense variant observed to cause a premature stop codon in a gene in which loss-of-function is an established disease mechanism (PVS1). The filtering allele frequency in gnomAD v4.1.0 is 0.0000002800 (2/1179170 alleles) in European (non-Finnish) population, which is lower than the ClinGen SCID VCEP threshold (<0.000115) for PM2_Supporting. Additionally, no homozygotes have been observed in gnomAD. (PM2_Supporting). At least one patient in the literature, LP1, presents JAk3 expression and phosphorylation absent; STAT5a phosphorylation is absent, and STAT6 phosphorylation is reduced. Thus: *Reduced or constitutive cytokine-induced tyrosine phosphorylation in patient cells (1pt) + *Reduced cytokine-induced phosphorylation of STAT5 in patient-derived T or B cells (1pt). Total 2 points, PP4_Moderate (PMID 9618765). In summary, this variant meets the criteria to be classified as Pathogenic for autosomal recessive T-B+ severe combined immunodeficiency due to JAK3 deficiency based on the ACMG/AMP criteria applied, as specified by the ClinGen SCID VCEP: PVS1, PM2_Supporting, and PP4_Moderate (VCEP specifications version 1).