17-50167695-G-T

Position:

• chr17-50167695-G-T

Variant summary

Our verdict is Pathogenic. Variant got 11 ACMG points: 11P and 0B. PM1 PM2 PM5 PP3_Strong PP5

The NM_000023.4(SGCA):​c.271G>T​(p.Gly91Cys) variant causes a missense change involving the alteration of a conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. G91R) has been classified as Likely pathogenic.

• Frequency: Genomes: not found (cov: 32)
• Consequence: SGCA NM_000023.4 missense
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:1 U:1
• Conservation: PhyloP100: 8.56

Genes affected

SGCA (HGNC:10805): (sarcoglycan alpha) This gene encodes a component of the dystrophin-glycoprotein complex (DGC), which is critical to the stability of muscle fiber membranes and to the linking of the actin cytoskeleton to the extracellular matrix. Its expression is thought to be restricted to striated muscle. Mutations in this gene result in type 2D autosomal recessive limb-girdle muscular dystrophy. Multiple transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Oct 2008]

ACMG classification

Verdict is Pathogenic. Variant got 11 ACMG points.

• PM1: In a topological_domain Extracellular (size 266) in uniprot entity SGCA_HUMAN there are 108 pathogenic changes around while only 2 benign (98%) in NM_000023.4
• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chrnull-null-null-null is described in UniProt as null.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.992
• PP5: Variant 17-50167695-G-T is Pathogenic according to our data. Variant chr17-50167695-G-T is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 538661.We mark this variant Likely_pathogenic, oryginal submissions are: {Uncertain_significance=1, Likely_pathogenic=1}.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
SGCA	NM_000023.4	c.271G>T	p.Gly91Cys	missense_variant	3/10	ENST00000262018.8	NP_000014.1
SGCA	NM_001135697.3	c.271G>T	p.Gly91Cys	missense_variant	3/8		NP_001129169.1
SGCA	NR_135553.2	n.307G>T		non_coding_transcript_exon_variant	3/9

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
SGCA	ENST00000262018.8	c.271G>T	p.Gly91Cys	missense_variant	3/10	1	NM_000023.4	ENSP00000262018.3

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome Cov.: 32

GnomAD4 genome Cov.: 32

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:1 Uncertain:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

Autosomal recessive limb-girdle muscular dystrophy type 2D Pathogenic:1 Uncertain:1

Uncertain significance, criteria provided, single submitter	clinical testing	Revvity Omics, Revvity	Feb 15, 2019	- -
Likely pathogenic, criteria provided, single submitter	clinical testing	Labcorp Genetics (formerly Invitae), Labcorp	Jul 19, 2022	Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) performed at Invitae indicates that this missense variant is expected to disrupt SGCA protein function. 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. This variant disrupts the p.Gly91 amino acid residue in SGCA. Other variant(s) that disrupt this residue have been observed in individuals with SGCA-related conditions (PMID: 17994539), which suggests that this may be a clinically significant amino acid residue. ClinVar contains an entry for this variant (Variation ID: 538661). This missense change has been observed in individual(s) with limb-girdle muscular dystrophy (Invitae). In at least one individual the data is consistent with being in trans (on the opposite chromosome) from a pathogenic variant. This variant is not present in population databases (gnomAD no frequency). This sequence change replaces glycine, which is neutral and non-polar, with cysteine, which is neutral and slightly polar, at codon 91 of the SGCA protein (p.Gly91Cys). -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.94
BayesDel_addAF	Pathogenic	0.55	D
BayesDel_noAF	Pathogenic	0.55
CADD	Pathogenic	32
DANN	Uncertain	1.0
DEOGEN2	Pathogenic	0.98	.;D
Eigen	Pathogenic	0.70
Eigen_PC	Uncertain	0.62
FATHMM_MKL	Pathogenic	0.99	D
LIST_S2	Uncertain	0.90	D;D
M_CAP	Pathogenic	0.48	D
MetaRNN	Pathogenic	0.99	D;D
MetaSVM	Pathogenic	1.0	D
MutationAssessor	Uncertain	2.5	M;M
PrimateAI	Uncertain	0.56	T
PROVEAN	Pathogenic	-6.8	D;D
REVEL	Pathogenic	0.97
Sift	Pathogenic	0.0	D;D
Sift4G	Pathogenic	0.0	D;D
Polyphen		1.0	D;D
Vest4		0.93
MutPred		0.92		Loss of disorder (P = 0.021);Loss of disorder (P = 0.021);
MVP		1.0
MPC		1.1
ClinPred		1.0	D
GERP RS		4.5
Varity_R		0.87
gMVP		0.98

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: rs890921874; hg19: chr17-48245056;