The c.1624G>A (NM_006218.4) variant in PIK3CA is a missense variant predicted to cause substitution of (p.Glu542Lys). Testing of unaffected and affected tissue show variable allelic fractions consistent with a post-zygotic event (PS2_Moderate; PMID: 22658544). The prevalence of the variant in affected individuals is significantly increased compared with the prevalence in controls (PS4_VS; PMIDs: 25722288, 25681199, 22658544, 29446767, 26851524, 25292196, 23100325; identified in 1 individual with neuroimaging demonstrating at least one large cerebral hemisphere with cortical malformation, at least 6 individuals with a clinical diagnosis of megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome; (MPPH) or megalencephaly-capillary malformation-polymicrogyria syndrome; (MCAP), at least 9 individuals with segmental overgrowth or vascular malformation of a limb or region of the body, and at least 9 tumor samples in the literature and COSMIC). This variant is absent from gnomAD v2.1.1 (PM2_Supporting). PIK3CA, in which the variant was identified, is defined by the ClinGen Brain Malformations Expert Panel as a gene that has a low rate of benign missense variation and where pathogenic missense variants are a common mechanism of disease (PP2). In summary, this variant meets the criteria to be classified as Pathogenic for mosaic autosomal dominant overgrowth with or without cerebral malformations due to abnormalities in MTOR-pathway genes based on the ACMG/AMP criteria applied, as specified by the ClinGen Brain Malformations Expert Panel: PS2_M, PS4_VS, PM2_P, PP2; 12 points (VCEP specifications version 1; Approved: 1/31/2021)