rs876657721

Positions:

• chr13-23335332-GAA-G

Variant summary

Our verdict is Pathogenic. Variant got 18 ACMG points: 18P and 0B. PVS1 PM2 PP5_Very_Strong

The NM_014363.6(SACS):​c.8542_8543del​(p.Phe2848ProfsTer14) variant causes a frameshift change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.000000684 in 1,461,668 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Likely pathogenic (★★).

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 6.8e-7 (0 hom.)
• Consequence: SACS NM_014363.6 frameshift
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:3
• Conservation: PhyloP100: 8.95

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 18 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 58 pathogenic variants in the truncated region.
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 13-23335332-GAA-G is Pathogenic according to our data. Variant chr13-23335332-GAA-G is described in ClinVar as [Likely_pathogenic]. Clinvar id is 228394.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
SACS	NM_014363.6	c.8542_8543del	p.Phe2848ProfsTer14	frameshift_variant	10/10	ENST00000382292.9	NP_055178.3

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
SACS	ENST00000382292.9	c.8542_8543del	p.Phe2848ProfsTer14	frameshift_variant	10/10	5	NM_014363.6	ENSP00000371729	P1

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome AF: 6.84e-7 AC: 1 AN: 1461668 Hom.: 0 AF XY: 0.00000138 AC XY: 1 AN XY: 727132

Gnomad4 AFR exome AF: 0.00

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: 8.99e-7

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 33

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:3

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Charlevoix-Saguenay spastic ataxia Pathogenic:2

Likely pathogenic, criteria provided, single submitter	clinical testing	Genome-Nilou Lab	Sep 05, 2021	- -
Likely pathogenic, criteria provided, single submitter	clinical testing	Counsyl	Apr 11, 2018	- -

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.Phe2848fs 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 2848 and leads to a premature termination codon 14 amino acids downstream. T his 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 v ariant is predicted to result in a truncated protein that is 1718 amino acids sh orter and lacks several functional domains of the normal protein. Loss of functi on variants in the SACS gene, most of which occur in exon 10, have been reported in several patients with ARSACS (Bouhlal 2011), and animal models support a los s of function mechanism of disease (Lariviere 2015). In summary, this variant me ets our criteria to be classified as pathogenic for ARSACS in an autosomal reces sive 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: rs876657721; hg19: chr13-23909471;