Our verdict is Uncertain significance. Variant got 2 ACMG points: 2P and 0B. PM2
The NM_006279.5(ST3GAL3):c.343C>T(p.Arg115Cys) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.0000118 in 1,614,048 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Uncertain significance (★★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. R115G) has been classified as Uncertain significance.
ST3GAL3 (HGNC:10866): (ST3 beta-galactoside alpha-2,3-sialyltransferase 3) The protein encoded by this gene is a type II membrane protein that catalyzes the transfer of sialic acid from CMP-sialic acid to galactose-containing substrates. The encoded protein is normally found in the Golgi apparatus but can be proteolytically processed to a soluble form. This protein is a member of glycosyltransferase family 29. Mutations in this gene have been associated with a form of autosomal recessive nonsymdromic cognitive disability as well as infantile epileptic encephalopathy. Multiple transcript variants encoding several different isoforms have been found for this gene. [provided by RefSeq, Jul 2017]
Uncertain significance, criteria provided, single submitter
clinical testing
Ambry Genetics
Dec 14, 2021
The c.343C>T (p.R115C) alteration is located in exon 6 (coding exon 5) of the ST3GAL3 gene. This alteration results from a C to T substitution at nucleotide position 343, causing the arginine (R) at amino acid position 115 to be replaced by a cysteine (C). Based on insufficient or conflicting evidence, the clinical significance of this alteration remains unclear. -
Early infantile epileptic encephalopathy with suppression bursts Uncertain:1
Uncertain significance, criteria provided, single submitter
clinical testing
Invitae
Jul 19, 2022
This sequence change replaces arginine, which is basic and polar, with cysteine, which is neutral and slightly polar, at codon 115 of the ST3GAL3 protein (p.Arg115Cys). This variant is not present in population databases (gnomAD no frequency). This variant has not been reported in the literature in individuals affected with ST3GAL3-related conditions. ClinVar contains an entry for this variant (Variation ID: 998398). Algorithms developed to predict the effect of missense changes on protein structure and function are either unavailable or do not agree on the potential impact of this missense change (SIFT: "Deleterious"; PolyPhen-2: "Possibly Damaging"; Align-GVGD: "Class C0"). In summary, the available evidence is currently insufficient to determine the role of this variant in disease. Therefore, it has been classified as a Variant of Uncertain Significance. -