The c.3140A>G (NM_006218.4) variant in PIK3CA is a missense variant predicted to cause substitution of (p.His1047Arg). This variant is present in one individual in gnomAD v2.1.1 (PM2_Supporting). The prevalence of the variant in affected individuals is significantly increased compared with the prevalence in controls (PS4_VS; PMIDs: 27191687, 28328134, 25292196, 22729222, 25424831, 465 entries in COSMIC, Segmental overgrowth or vascular malformation of a limb or region of the body, present in patient derived cell lines). 60 independent Ba/F3 and 57 independent MCF10A experiments showed this variant has a proliferative effect indicating that this variant impacts protein function (PMID:29533785 ) (PS3_Moderate). This variant resides within the kinase domain of PIK3CA that is defined as a critical functional domain by the ClinGen BMEP (PMIDs: 26637981, 24459181, 27631024) (PM1_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). Testing of unaffected and affected tissue show variable allelic fractions consistent with a post-zygotic event (PS2_Moderate; PMID: 25424831). 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: PM2_P, PS4_VS, PS3_M, PM1_P, PP2, PS2_M; 15 points (VCEP specifications version 1; Approved: 1/31/2021)