rs781163821

Variant names:

• chr19-1397401-G-GT
• rs781163821
• NM_000156.6:c.668dupA

Variant summary

Our verdict is Uncertain significance. The variant received 3 ACMG points: 3P and 0B. PM2_Supporting PVS1_Moderate

This summary comes from the ClinGen Evidence Repository: The NM_000156.6:c.668dupA (p.Tyr223fs) variant in GAMT is a frameshift variant in the last exon (exon 6/6; amino acid 223/237) of GAMT, and is therefore predicted to escape nonsense mediated decay. Less than 10% of the protein is predicted to be removed (PVS1_Moderate). The highest population minor allele frequency in gnomAD v4.1.0 is 0.000002543 (3/1179898 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). To our knowledge, this variant has not been reported in published literature in individuals with GAMT deficiency. However, itt is noted in ClinVar (Variation ID 445930). In addition, a different nucleotide change that results in the same molecular consequence (c.669C>G (p.Tyr223Ter), has also been reported in ClinVar (Variation ID: 1394775).In summary, this variant meets the criteria to be classified as a variant of uncertain significance for GAMT deficiency. GAMT-specific ACMG/AMP codes met, as specified by the ClinGen Cerebral Creatine Deficiency Syndromes VCEP (Specifications Version 2.0.0): PVS1_Moderate, PM2_Supporting(Classification approved by the ClinGen CCDS VCEP on April 28, 2025). LINK:https://erepo.genome.network/evrepo/ui/classification/CA9043535/MONDO:0012999/026

• Frequency:
  • Genomes: 𝑓 0.0000066 (0 hom., cov: 33)
  • Exomes 𝑓: 0.0000014 (0 hom.)
• Consequence: GAMT NM_000156.6 frameshift, stop_gained
• Clinical Significance: Uncertain significance reviewed by expert panel U:4
• Conservation: PhyloP100: 6.00
• Publications: 0 publications found

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 Gene-Disease associations (from GenCC):

• guanidinoacetate methyltransferase deficiency

  Inheritance: AR Classification: DEFINITIVE, STRONG, SUPPORTIVE Submitted by: Orphanet, G2P, Labcorp Genetics (formerly Invitae), ClinGen, Ambry Genetics

ACMG classification

Our verdict: Uncertain_significance. The variant received 3 ACMG points.

• PVS1: For more information check the summary or visit ClinGen Evidence Repository.
• PM2: For more information check the summary or visit ClinGen Evidence Repository.

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_000156.6. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Sel.	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	GAMT	NM_000156.6	MANE Select	c.668dupA	p.Tyr223fs	frameshift stop_gained	Exon 6 of 6	NP_000147.1

Ensembl Transcripts

Sel.	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	GAMT	ENST00000252288.8	TSL:1 MANE Select	c.668dupA	p.Tyr223fs	frameshift stop_gained	Exon 6 of 6	ENSP00000252288.1
	GAMT	ENST00000902474.1		c.938dupA	p.Tyr313fs	frameshift stop_gained	Exon 6 of 6	ENSP00000572533.1
	GAMT	ENST00000902472.1		c.671dupA	p.Tyr224fs	frameshift stop_gained	Exon 6 of 6	ENSP00000572531.1

Frequencies

GnomAD3 genomes AF: 0.00000657 AC: 1 AN: 152200 Hom.: 0 Cov.: 33

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: 0.0000147

Gnomad OTH AF: 0.00

GnomAD2 exomes AF: 0.00000403 AC: 1 AN: 248204 AF XY: 0.00000742

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 FIN exome AF: 0.00

Gnomad NFE exome AF: 0.00000890

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.00000137 AC: 2 AN: 1460102 Hom.: 0 Cov.: 30 AF XY: 0.00000275 AC XY: 2 AN XY: 726362

African (AFR) AF: 0.00 AC: 0 AN: 33476

American (AMR) AF: 0.00 AC: 0 AN: 44706

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26118

East Asian (EAS) AF: 0.00 AC: 0 AN: 39694

South Asian (SAS) AF: 0.00 AC: 0 AN: 86250

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 51848

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5764

European-Non Finnish (NFE) AF: 0.00000180 AC: 2 AN: 1111876

Other (OTH) AF: 0.00 AC: 0 AN: 60370

GnomAD4 genome AF: 0.00000657 AC: 1 AN: 152200 Hom.: 0 Cov.: 33 AF XY: 0.00 AC XY: 0 AN XY: 74352

African (AFR) AF: 0.00 AC: 0 AN: 41444

American (AMR) AF: 0.00 AC: 0 AN: 15286

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 3472

East Asian (EAS) AF: 0.00 AC: 0 AN: 5198

South Asian (SAS) AF: 0.00 AC: 0 AN: 4834

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 10624

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 316

European-Non Finnish (NFE) AF: 0.0000147 AC: 1 AN: 68022

Other (OTH) AF: 0.00 AC: 0 AN: 2092

Alfa AF: 0.0000712 Hom.: 0

Bravo AF: 0.0000113

ClinVar

ClinVar submissions as Germline

Significance: Uncertain significance

Revision: reviewed by expert panel

Pathogenic	VUS	Benign	Condition
-	2	-	Deficiency of guanidinoacetate methyltransferase (2)
-	1	-	Cerebral creatine deficiency syndrome (1)
-	1	-	not provided (1)

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
PhyloP100		6.0
Mutation Taster		=19/181	disease causing

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.0		Details are displayed if max score is > 0.2

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

Other links and lift over

dbSNP: rs781163821; hg19: chr19-1397400;