NM_000022.4 :c.646G>A is a missense variant predicted to cause substitution of Glycine by Arginine at amino acid 216 (p.Gly216Arg). The filtering allele frequency (the upper threshold of the 95% CI of 46/1180026) of the c.646G>A variant in ADA is 0.00002743 for European Non-Finnish chromosomes by gnomAD v4, which is lower than the ClinGen SCID VCEP threshold (<0.0001742) for PM2_Supporting, and therefore meets this criterion (PM2_Supporting).The variant has been reported to segregate with SCID in 4 affected family members from 2 families (PP1_strong; PMID : 26255240). This variant has been detected in 15 individuals with ADA deficient SCID. Of those individuals, 3 were compound heterozygous for the variant and a pathogenic variant (Glu319Glyfs*320 ,confirmed in trans ,1pt.). 12 individuals were homozygous for the variant (1 pt.) (total: 2 pts; PM3_Strong ,PMID : 26255240). Male patient with SCID (0.5 pt.), genome sequencing conducted (0.5 pt.), reduced ADA enzyme activity in patient cells (1 pt),SCID phenotype corrected by exogenous ADA supplementation (1 pt.),Increased dATP in pretreatment erythrocytes (2 pts.). (PP4_Moderate (5 pts.), PMID: 1680289). ADA activity in SØ3834 was 30.4 nmol/h/mg protein which is .012 % of wild type ADA activity indicating that this variant impacts protein function (PMID : 9758612, PS3_Moderate). Based on the above evidence, the variant may be classified as pathogenic for autosomal recessive severe combined immunodeficiency due to ADA deficiency based on the ACMG/AMP criteria applied, as specified by the ClinGen SCID VCEP: PP1_strong,PM2_supporting,PM3_strong,PP4_moderate,PS3_moderate (VCEP specifications version 1).