chr19-1399509-C-A
Variant summary
Our verdict is Likely pathogenic. Variant got 7 ACMG points: 7P and 0B. PM3_SupportingPP4_StrongPM2_SupportingPP3
This summary comes from the ClinGen Evidence Repository: The NM_000156.6:c.391+15G>T variant is in intron 3 of GAMT. The computational predictor, SpliceAI, predicts the creation of a new donor splice site 2 bp upstream (score 0.98) indicating that this variants may impact splicing (PP3). This variant has been identified a homozygous individual with clinical features consistent with GAMT deficiency, "decreased" GAMT enzyme activity in fibroblasts, elevated GAA and low or low normal creatine in urine, low creatine on brain MRS (PMID:23234264, 29506905; assumed to be the same patent in both publications) (PP4_Strong, PM3_Supporting). The highest population minor allele frequency in gnomAD v4.1.0 is 0.00003651 (43/1177768 alleles) in the European (non-Finnish) population, which is lower than the ClinGen CCDS VCEP’s threshold for PM2_Supporting (<0.0004), meeting this criterion (PM2_Supporting). There is a ClinVar entry for this variant (ClinVar Variation ID: 544259). In summary, this variant meets the criteria to be classified as likely pathogenic for GAMT deficiency. GAMT-specific ACMG/AMP criteria applied, as specified by the ClinGen Cerebral Creatine Deficiency Syndromes Variant Curation Expert Panel (Specifications Version 2.0.0): PP4_Strong, PP3, PM2_Supporting, PM3_Supporting.(Classification approved by the ClinGen Cerebral Creatine Deficiency Syndromes Variant Curation Expert Panel on November 14, 2024) LINK:https://erepo.genome.network/evrepo/ui/classification/CA9043702/MONDO:0012999/026
Frequency
Consequence
NM_000156.6 intron
Scores
Clinical Significance
Conservation
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ACMG classification
Verdict is Likely_pathogenic. Variant got 7 ACMG points.
Transcripts
RefSeq
Ensembl
Frequencies
GnomAD3 genomes AF: 0.0000131 AC: 2AN: 152180Hom.: 0 Cov.: 32
GnomAD3 exomes AF: 0.0000122 AC: 3AN: 244900Hom.: 0 AF XY: 0.00000753 AC XY: 1AN XY: 132848
GnomAD4 exome AF: 0.0000288 AC: 42AN: 1457304Hom.: 0 Cov.: 32 AF XY: 0.0000248 AC XY: 18AN XY: 724748
GnomAD4 genome AF: 0.0000131 AC: 2AN: 152180Hom.: 0 Cov.: 32 AF XY: 0.0000269 AC XY: 2AN XY: 74332
ClinVar
Submissions by phenotype
Cerebral creatine deficiency syndrome Pathogenic:1Uncertain:1
Uncertain significance, criteria provided, single submitter | curation | Broad Center for Mendelian Genomics, Broad Institute of MIT and Harvard | Nov 02, 2021 | The c.391+15G>T variant in GAMT has been reported in 1 homozygous individual with cerebral creatine deficiency syndrome (PMID: 23234264) and has been identified in in 0.003% (4/125836) of European (non-Finnish) chromosomes by the Genome Aggregation Database (gnomAD, http://gnomad.broadinstitute.org; dbSNP ID: rs367567416). Although this variant has been seen in the general population in a heterozygous state, its frequency is low enough to be consistent with a recessive carrier frequency. This variant has also been reported in ClinVar (Variation ID#: 544259) and has been interpreted as VUS by Invitae. This variant is located in the 3' splice region. In vitro functional studies provide some evidence that the c.391+15G>T variant may slightly impact protein function (PMID: 23234264). However, these types of assays may not accurately represent biological function. Computational tools do suggest an impact to splicing. However, this information is not predictive enough to determine pathogenicity. In summary, the clinical significance of the c.391+15G>T variant is uncertain. ACMG/AMP Criteria applied: PM2_supporting, PS3_supporting, PM3_supporting, PP3 (Richards 2015). - |
Likely pathogenic, criteria provided, single submitter | clinical testing | Labcorp Genetics (formerly Invitae), Labcorp | Jun 11, 2024 | This sequence change falls in intron 3 of the GAMT gene. It does not directly change the encoded amino acid sequence of the GAMT protein. This variant is present in population databases (rs367567416, gnomAD 0.004%). This variant has been observed in individual(s) with primary creatine disorder and GAMT deficiency (PMID: 23234264). ClinVar contains an entry for this variant (Variation ID: 544259). Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may disrupt the consensus splice site. In summary, the currently available evidence indicates that the variant is pathogenic, but additional data are needed to prove that conclusively. Therefore, this variant has been classified as Likely Pathogenic. - |
not specified Uncertain:1
Uncertain significance, criteria provided, single submitter | clinical testing | Women's Health and Genetics/Laboratory Corporation of America, LabCorp | Sep 28, 2022 | Variant summary: GAMT c.391+15G>T alters a non-conserved nucleotide located close to a canonical splice site and therefore could affect mRNA splicing, leading to a significantly altered protein sequence. Several computational tools predict a significant impact on normal splicing: Four predict the variant creates a novel 5' donor site within intron 3. However, these predictions have yet to be confirmed by functional studies. The variant allele was found at a frequency of 1.2e-05 in 244900 control chromosomes (gnomAD). c.391+15G>T has been reported in the literature as a homozygous genotype in an individual affected with Cerebral Creatine Deficiency Syndrome (e.g. Cheillan_2012). Enzyme studies in cells from this individual confirmed deficient GAMT activity, however to our knowledge, no additional experimental evidence demonstrating an impact on protein function has been reported. Two submitters have provided clinical-significance assessments for this variant to ClinVar after 2014 and both classified the variant as uncertain significance. Based on the evidence outlined above, the variant was classified as VUS-possibly pathogenic. - |
Computational scores
Source:
Splicing
Find out detailed SpliceAI scores and Pangolin per-transcript scores at