rs876657720

Positions:

• chr13-23336234-C-CT

Variant summary

Our verdict is Pathogenic. Variant got 12 ACMG points: 12P and 0B. PVS1 PM2 PP5_Moderate

The NM_014363.6(SACS):​c.7641_7642insA​(p.Glu2548ArgfsTer7) variant causes a frameshift change involving the alteration of a non-conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. Variant has been reported in ClinVar as Pathogenic (★). Synonymous variant affecting the same amino acid position (i.e. K2547K) has been classified as Likely benign.

• Frequency: Genomes: not found (cov: 33)
• Consequence: SACS NM_014363.6 frameshift
• Clinical Significance: Pathogenic criteria provided, single submitter P:1
• Conservation: PhyloP100: 1.69

Genes affected

SACS (HGNC:10519): (sacsin molecular chaperone) This gene encodes the sacsin protein, which includes a UbL domain at the N-terminus, a DnaJ domain, and a HEPN domain at the C-terminus. The gene is highly expressed in the central nervous system, also found in skin, skeletal muscles and at low levels in the pancreas. This gene includes a very large exon spanning more than 12.8 kb. Mutations in this gene result in autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS), a neurodegenerative disorder characterized by early-onset cerebellar ataxia with spasticity and peripheral neuropathy. The authors of a publication on the effects of siRNA-mediated sacsin knockdown concluded that sacsin protects against mutant ataxin-1 and suggest that "the large multi-domain sacsin protein is able to recruit Hsp70 chaperone action and has the potential to regulate the effects of other ataxia proteins" (Parfitt et al., PubMed: 19208651). A pseudogene associated with this gene is located on chromosome 11. Alternative splicing of this gene results in multiple transcript variants. [provided by RefSeq, May 2013]

ACMG classification

Verdict is Pathogenic. Variant got 12 ACMG points.

• PVS1: Loss of function variant, product does not undergo nonsense mediated mRNA decay. Variant is located in the 3'-most exon, not predicted to undergo nonsense mediated mRNA decay. There are 245 pathogenic variants in the truncated region.
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 13-23336234-C-CT is Pathogenic according to our data. Variant chr13-23336234-C-CT is described in ClinVar as [Pathogenic]. Clinvar id is 228393.Status of the report is criteria_provided_single_submitter, 1 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
SACS	NM_014363.6	c.7641_7642insA	p.Glu2548ArgfsTer7	frameshift_variant	10/10	ENST00000382292.9

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
SACS	ENST00000382292.9	c.7641_7642insA	p.Glu2548ArgfsTer7	frameshift_variant	10/10	5	NM_014363.6	P1

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome Cov.: 37

GnomAD4 genome Cov.: 33

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:1

Revision: criteria provided, single submitter

Submissions by phenotype

Autosomal recessive spastic ataxia Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

Laboratory for Molecular Medicine, Mass General Brigham Personalized Medicine

Aug 08, 2015

The p.Glu2548fs variant in SACS has not been previously reported in individuals with clinical features of autosomal recessive spastic ataxia of Charlevoix-Sague nay (ARSACS) or in large population studies. This variant is predicted to cause a frameshift, which alters the protein?s amino acid sequence beginning at positi on 2548 and leads to a premature termination codon 7 amino acids downstream. Thi s premature termination codon occurs within the last exon of the gene (exon 10), and is more likely to escape nonsense mediated decay (NMD). Therefore, this var iant is predicted to result in a truncated protein that is 2025 amino acids shor ter and lacks several functional domains of the normal protein. Loss of function variants in the SACS gene, most of which occur in exon 10, have been reported i n several patients with ARSACS (Bouhlal 2011), and animal models support a loss of function mechanism of disease (Lariviere 2015). In summary, this variant meet s our criteria to be classified as pathogenic for ARSACS in an autosomal recessi ve manner (http://www.partners.org/personalizedmedicine/LMM). -

Computational scores

Source: dbNSFP v4.3

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

Publications

LitVar

Other links and lift over

dbSNP: rs876657720; hg19: chr13-23910373;