rs60407644

Positions:

• chr17-50167487-G-A

Variant summary

Our verdict is Uncertain significance. Variant got 5 ACMG points: 5P and 0B. PM1 PM2 PP5

The ENST00000262018.8(SGCA):​c.157G>A​(p.Ala53Thr) variant causes a missense, splice region change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000752 in 1,461,860 control chromosomes in the GnomAD database, with no homozygous occurrence. 3/3 splice prediction tools predicting alterations to normal splicing. 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. A53S) has been classified as Uncertain significance.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000075 (0 hom.)
• Consequence: SGCA ENST00000262018.8 missense, splice_region
• Scores: Splicing: ADA: 0.9998
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:4 U:1
• Conservation: PhyloP100: 2.71

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 Uncertain_significance. Variant got 5 ACMG points.

• PM1: In a topological_domain Extracellular (size 266) in uniprot entity SGCA_HUMAN there are 171 pathogenic changes around while only 10 benign (94%) in ENST00000262018.8
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 17-50167487-G-A is Pathogenic according to our data. Variant chr17-50167487-G-A is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 281859.We mark this variant Likely_pathogenic, oryginal submissions are: {Likely_pathogenic=2, Pathogenic=2, Uncertain_significance=1}. Variant chr17-50167487-G-A is described in Lovd as [Pathogenic].

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
SGCA	NM_000023.4	c.157G>A	p.Ala53Thr	missense_variant, splice_region_variant	2/10	ENST00000262018.8	NP_000014.1
SGCA	NM_001135697.3	c.157G>A	p.Ala53Thr	missense_variant, splice_region_variant	2/8		NP_001129169.1
SGCA	NR_135553.2	n.193G>A		splice_region_variant, non_coding_transcript_exon_variant	2/9

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
SGCA	ENST00000262018.8	c.157G>A	p.Ala53Thr	missense_variant, splice_region_variant	2/10	1	NM_000023.4	ENSP00000262018	P1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD3 exomes AF: 0.00000796 AC: 2 AN: 251404 Hom.: 0 AF XY: 0.00 AC XY: 0 AN XY: 135896

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.0000289

Gnomad ASJ exome AF: 0.00

Gnomad EAS exome AF: 0.0000544

Gnomad SAS exome AF: 0.00

Gnomad FIN exome AF: 0.00

Gnomad NFE exome AF: 0.00

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.00000752 AC: 11 AN: 1461860 Hom.: 0 Cov.: 32 AF XY: 0.00000963 AC XY: 7 AN XY: 727238

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.0000224

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.0000252

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.00000809

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 32

Bravo AF: 0.00000378

ExAC AF: 0.00000824 AC: 1

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:4 Uncertain:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

Autosomal recessive limb-girdle muscular dystrophy type 2D Pathogenic:3

Likely pathogenic, criteria provided, single submitter	clinical testing	Revvity Omics, Revvity	Jan 16, 2020	- -
Pathogenic, criteria provided, single submitter	clinical testing	Labcorp Genetics (formerly Invitae), Labcorp	Mar 20, 2023	This sequence change replaces alanine, which is neutral and non-polar, with threonine, which is neutral and polar, at codon 53 of the SGCA protein (p.Ala53Thr). This variant also falls at the last nucleotide of exon 2, which is part of the consensus splice site for this exon. For these reasons, this variant has been classified as Pathogenic. Variants that disrupt the consensus splice site are a relatively common cause of aberrant splicing (PMID: 17576681, 9536098). Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may disrupt the consensus splice site. An algorithm developed to predict the effect of missense changes on protein structure and function (PolyPhen-2) suggests that this variant  is likely to be tolerated. ClinVar contains an entry for this variant (Variation ID: 281859). This missense change has been observed in individual(s) with limb girdle muscular dystrophy (LGMD) (PMID: 11693784, 16616845, 18285821; Invitae). In at least one individual the data is consistent with being in trans (on the opposite chromosome) from a pathogenic variant. It has also been observed to segregate with disease in related individuals. This variant is present in population databases (rs60407644, gnomAD 0.006%). -
Likely pathogenic, criteria provided, single submitter	clinical testing	Baylor Genetics	Sep 06, 2023	- -

Autosomal recessive limb-girdle muscular dystrophy Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

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

May 17, 2024

Variant summary: SGCA c.157G>A (p.Ala53Thr) results in a non-conservative amino acid change in the encoded protein sequence. Three of five in-silico tools predict a damaging effect of the variant on protein function. Several computational tools predict a significant impact on normal splicing: Two predict the variant abolishes a 5' splicing donor site whereas two predict the variant significantly weakens a 5' donor site. At least one publication reports experimental evidence that this variant results in skipping of exon 2 and 3 in RT-PCR analysis of SGCA mRNA in muscle tissue from a c.157G>A carrier (Escobar_2021). The variant allele was found at a frequency of 8e-06 in 251404 control chromosomes. c.157G>A has been reported in the literature as homozygous or in compound heterozygous state with a pathogenic variant in multiple individuals affected with Autosomal Recessive Limb-Girdle Muscular Dystrophy (Fendri_2006, Trabelsi_2008, Megarbane_2021). These data indicate that the variant is very likely to be associated with disease. The following publications have been ascertained in the context of this evaluation (PMID: 33848270, 16616845, 34602496, 18285821). ClinVar contains an entry for this variant (Variation ID: 281859). Based on the evidence outlined above, the variant was classified as pathogenic. -

not provided Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Eurofins Ntd Llc (ga)

Jul 30, 2015

- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Benign	0.070
BayesDel_addAF	Uncertain	0.14	D
BayesDel_noAF	Uncertain	0.13
CADD	Uncertain	24
DANN	Uncertain	0.99
DEOGEN2	Uncertain	0.61	.;D
Eigen	Benign	-0.36
Eigen_PC	Benign	-0.44
FATHMM_MKL	Benign	0.58	D
LIST_S2	Benign	0.78	T;T
M_CAP	Benign	0.052	D
MetaRNN	Uncertain	0.57	D;D
MetaSVM	Uncertain	0.26	D
MutationTaster	Benign	1.0	D;N;N;N
PrimateAI	Benign	0.40	T
PROVEAN	Benign	-0.31	N;N
REVEL	Uncertain	0.63
Sift	Benign	0.071	T;T
Sift4G	Benign	0.28	T;T
Polyphen		0.96	D;P
Vest4		0.15
MutPred		0.79		Gain of glycosylation at A53 (P = 0.0103);Gain of glycosylation at A53 (P = 0.0103);
MVP		0.96
MPC		0.36
ClinPred		0.64	D
GERP RS		1.4
Varity_R		0.052
gMVP		0.63

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	1.0
dbscSNV1_RF	Pathogenic	0.88
SpliceAI score (max)		0.84		Details are displayed if max score is > 0.2
DS_DG_spliceai		0.31		Position offset: -4
DS_DL_spliceai		0.84		Position offset: 0

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

Publications

LitVar

Other links and lift over

dbSNP: rs60407644; hg19: chr17-48244848; COSMIC: COSV56248916; COSMIC: COSV56248916;