The c.187A>G (NM_000215.4) variant in JAK3 is a missense variant predicted to cause the substitution of Isoleucine by Valine at amino acid 63 (p.Ile63Val). The popmax filtering allele frequency (the upper threshold of the 95% CI) of this variant is 0.00007135 (105/1179936 alleles) for European (non-Finnish) chromosomes by gnomAD v.4, which is lower than the ClinGen SCID VCEP threshold (<0.000115) for PM2_Supporting; However, the highest MAF in the Ashkenazi Jewish population is 0.007061 (209/29600 alleles), which is above the SCID VCEP established threshold of >0.00100 for BS1. As this population is not known to have a higher prevalence, this is considered to meet BS1. One homozygote is described in gnomAD v.4 in the Ashkenazi Jewish population (BS2_Supporting). To our knowledge, this variant has not been reported in the literature in individuals affected with JAk3-SCID/related conditions or in functional studies. In summary, this variant meets the criteria to be classified as Likely Benign 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. Criteria applied: BS1 and BS2_Supporting (VCEP specifications version 1.0).