chr19-1399509-C-A

Variant names:

Variant summary

Our verdict is Likely pathogenic. Variant got 7 ACMG points: 7P and 0B. PP3PM2_SupportingPM3_SupportingPP4_Strong

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

Clinical Significance

Likely pathogenic reviewed by expert panel P:2U: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]

GAMT links:

Genome browser will be placed here

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
GAMT	NM_000156.6 link	c.391+15G>T		intron_variant	Intron 3 of 5	ENST00000252288.8	NP_000147.1	Q14353-1V9HWB2
GAMT	NM_138924.3 link	c.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
GAMT	ENST00000252288.8 link	c.391+15G>T		intron_variant	Intron 3 of 5	1	NM_000156.6	ENSP00000252288.1		Q14353-1

Frequencies

GnomAD3 genomes

AF:

0.0000131

AC:

AN:

152180

Hom.:

Cov.:

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:

AN:

244900

Hom.:

AF XY:

0.00000753

AC XY:

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:

AN:

1457304

Hom.:

Cov.:

AF XY:

0.0000248

AC XY:

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:

AN:

152180

Hom.:

Cov.:

AF XY:

0.0000269

AC XY:

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.:

ClinVar

Significance: Likely pathogenic

Submissions summary: Pathogenic:2Uncertain:2

Revision: reviewed by expert panel

LINK: link

Submissions by phenotype

Cerebral creatine deficiency syndrome

Pathogenic:1Uncertain:1

Nov 02, 2021

Broad Center for Mendelian Genomics, Broad Institute of MIT and Harvard

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: curation

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). -

Jun 11, 2024

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

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. -

Deficiency of guanidinoacetate methyltransferase

Pathogenic:1

Nov 14, 2024

ClinGen Cerebral Creatine Deficiency Syndromes Variant Curation Expert Panel, ClinGen

Significance: Likely pathogenic

Review Status: reviewed by expert panel

Collection Method: curation

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) -

not specified

Uncertain:1

Sep 28, 2022

Women's Health and Genetics/Laboratory Corporation of America, LabCorp

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

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: 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.

Variant summary

Frequency

Consequence

Scores

Clinical Significance

Conservation

ACMG classification

Transcripts

RefSeq

Ensembl

Frequencies

ClinVar

Submissions by phenotype

Computational scores

Splicing

Publications

LitVar

Other links and lift over