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

Genomes: 𝑓 0.000013 ( 0 hom., cov: 32)
Exomes 𝑓: 0.000029 ( 0 hom. )

Consequence

GAMT
NM_000156.6 intron

Scores

2

Clinical Significance

Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:1U:2

Conservation

PhyloP100: -0.601
Variant links:
Genes affected
GAMT (HGNC:4136): (guanidinoacetate N-methyltransferase) The protein encoded by this gene is a methyltransferase that converts guanidoacetate to creatine, using S-adenosylmethionine as the methyl donor. Defects in this gene have been implicated in neurologic syndromes and muscular hypotonia, probably due to creatine deficiency and accumulation of guanidinoacetate in the brain of affected individuals. Two transcript variants encoding different isoforms have been described for this gene. Pseudogenes of this gene are found on chromosomes 2 and 13. [provided by RefSeq, Feb 2012]

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ACMG classification

Classification made for transcript

Verdict is Likely_pathogenic. Variant got 7 ACMG points.

PM2
For more information check the summary or visit ClinGen Evidence Repository.
PM3
For more information check the summary or visit ClinGen Evidence Repository.
PP3
For more information check the summary or visit ClinGen Evidence Repository.
PP4
For more information check the summary or visit ClinGen Evidence Repository.

Transcripts

RefSeq

Gene Transcript HGVSc HGVSp Effect Exon rank MANE Protein UniProt
GAMTNM_000156.6 linkc.391+15G>T intron_variant Intron 3 of 5 ENST00000252288.8 NP_000147.1 Q14353-1V9HWB2
GAMTNM_138924.3 linkc.391+15G>T intron_variant Intron 3 of 4 NP_620279.1 Q14353-2

Ensembl

Gene Transcript HGVSc HGVSp Effect Exon rank TSL MANE Protein Appris UniProt
GAMTENST00000252288.8 linkc.391+15G>T intron_variant Intron 3 of 5 1 NM_000156.6 ENSP00000252288.1 Q14353-1

Frequencies

GnomAD3 genomes
AF:
0.0000131
AC:
2
AN:
152180
Hom.:
0
Cov.:
32
show subpopulations
Gnomad AFR
AF:
0.00
Gnomad AMI
AF:
0.00
Gnomad AMR
AF:
0.00
Gnomad ASJ
AF:
0.00
Gnomad EAS
AF:
0.00
Gnomad SAS
AF:
0.00
Gnomad FIN
AF:
0.00
Gnomad MID
AF:
0.00
Gnomad NFE
AF:
0.0000294
Gnomad OTH
AF:
0.00
GnomAD3 exomes
AF:
0.0000122
AC:
3
AN:
244900
Hom.:
0
AF XY:
0.00000753
AC XY:
1
AN XY:
132848
show subpopulations
Gnomad AFR exome
AF:
0.00
Gnomad AMR exome
AF:
0.00
Gnomad ASJ exome
AF:
0.00
Gnomad EAS exome
AF:
0.00
Gnomad SAS exome
AF:
0.00
Gnomad FIN exome
AF:
0.00
Gnomad NFE exome
AF:
0.0000272
Gnomad OTH exome
AF:
0.00
GnomAD4 exome
AF:
0.0000288
AC:
42
AN:
1457304
Hom.:
0
Cov.:
32
AF XY:
0.0000248
AC XY:
18
AN XY:
724748
show subpopulations
Gnomad4 AFR exome
AF:
0.0000299
Gnomad4 AMR exome
AF:
0.00
Gnomad4 ASJ exome
AF:
0.00
Gnomad4 EAS exome
AF:
0.00
Gnomad4 SAS exome
AF:
0.00
Gnomad4 FIN exome
AF:
0.00
Gnomad4 NFE exome
AF:
0.0000369
Gnomad4 OTH exome
AF:
0.00
GnomAD4 genome
AF:
0.0000131
AC:
2
AN:
152180
Hom.:
0
Cov.:
32
AF XY:
0.0000269
AC XY:
2
AN XY:
74332
show subpopulations
Gnomad4 AFR
AF:
0.00
Gnomad4 AMR
AF:
0.00
Gnomad4 ASJ
AF:
0.00
Gnomad4 EAS
AF:
0.00
Gnomad4 SAS
AF:
0.00
Gnomad4 FIN
AF:
0.00
Gnomad4 NFE
AF:
0.0000294
Gnomad4 OTH
AF:
0.00
Alfa
AF:
0.000111
Hom.:
0

ClinVar

Significance: Conflicting classifications of pathogenicity
Submissions summary: Pathogenic:1Uncertain:2
Revision: criteria provided, conflicting classifications
LINK: link

Submissions by phenotype

Cerebral creatine deficiency syndrome Pathogenic:1Uncertain:1
Uncertain significance, criteria provided, single submittercurationBroad Center for Mendelian Genomics, Broad Institute of MIT and HarvardNov 02, 2021The 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 submitterclinical testingLabcorp Genetics (formerly Invitae), LabcorpJun 11, 2024This 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 submitterclinical testingWomen's Health and Genetics/Laboratory Corporation of America, LabCorpSep 28, 2022Variant 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: dbNSFP v4.3

Name
Calibrated prediction
Score
Prediction
BayesDel_noAF
Benign
-0.61
CADD
Benign
2.0
DANN
Benign
0.95
RBP_binding_hub_radar
0.0
RBP_regulation_power_radar
1.1

Splicing

Name
Calibrated prediction
Score
Prediction
SpliceAI score (max)
0.98
Details are displayed if max score is > 0.2
DS_DG_spliceai
0.98
Position offset: 2

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Publications

LitVar

Below is the list of publications found by LitVar. It may be empty.

Other links and lift over

dbSNP: rs367567416; hg19: chr19-1399508; API