rs1167723109

Positions:

• chr6-129154683-G-C

Variant summary

Our verdict is Likely pathogenic. Variant got 6 ACMG points: 6P and 0B. PM2 PP3_Strong

The NM_000426.4(LAMA2):​c.1206G>C​(p.Gly402=) variant causes a splice region, synonymous change. The variant allele was found at a frequency of 0.000000685 in 1,460,124 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a benign outcome for this variant. 3/3 splice prediction tools predicting alterations to normal splicing. Variant has been reported in ClinVar as Uncertain significance (★★).

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 6.8e-7 (0 hom.)
• Consequence: LAMA2 NM_000426.4 splice_region, synonymous
• Scores: Splicing: ADA: 1.000
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:2
• Conservation: PhyloP100: 4.76

Genes affected

LAMA2 (HGNC:6482): (laminin subunit alpha 2) Laminin, an extracellular protein, is a major component of the basement membrane. It is thought to mediate the attachment, migration, and organization of cells into tissues during embryonic development by interacting with other extracellular matrix components. It is composed of three subunits, alpha, beta, and gamma, which are bound to each other by disulfide bonds into a cross-shaped molecule. This gene encodes the alpha 2 chain, which constitutes one of the subunits of laminin 2 (merosin) and laminin 4 (s-merosin). Mutations in this gene have been identified as the cause of congenital merosin-deficient muscular dystrophy. Two transcript variants encoding different proteins have been found for this gene. [provided by RefSeq, Jul 2008]

ACMG classification

Verdict is Likely_pathogenic. Variant got 6 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP3: Splicing scoreres supports a deletorius effect: Scorers claiming Pathogenic: dbscSNV1_ADA, dbscSNV1_RF, max_spliceai. No scorers claiming Uncertain. No scorers claiming Benign.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
LAMA2	NM_000426.4	c.1206G>C	p.Gly402=	splice_region_variant, synonymous_variant	8/65	ENST00000421865.3	NP_000417.3
LAMA2	NM_001079823.2	c.1206G>C	p.Gly402=	splice_region_variant, synonymous_variant	8/64		NP_001073291.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
LAMA2	ENST00000421865.3	c.1206G>C	p.Gly402=	splice_region_variant, synonymous_variant	8/65	5	NM_000426.4	ENSP00000400365

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD3 exomes AF: 0.00000398 AC: 1 AN: 250970 Hom.: 0 AF XY: 0.00000737 AC XY: 1 AN XY: 135728

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.0000290

Gnomad ASJ exome AF: 0.00

Gnomad EAS exome AF: 0.00

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: 6.85e-7 AC: 1 AN: 1460124 Hom.: 0 Cov.: 30 AF XY: 0.00000138 AC XY: 1 AN XY: 726464

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.0000224

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: 0.00

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 32

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:2

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

LAMA2-related muscular dystrophy Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Jun 09, 2019

In summary, this is a novel silent change with uncertain impact on splicing. It has been classified as a Variant of Uncertain Significance. Nucleotide substitutions within the consensus splice site are relatively common causes of aberrant splicing (PMID: 17576681, 9536098). Algorithms developed to predict the effect of nucleotide changes on RNA splicing suggest that this variant may alter RNA splicing, but this prediction has not been confirmed by published transcriptional studies. This variant is not present in population databases (ExAC no frequency) and has not been reported in the literature in individuals with a LAMA2-related disease. This sequence change affects codon 402 of the LAMA2 mRNA. It is a 'silent' change, meaning that it does not change the encoded amino acid sequence of the LAMA2 protein. This variant also falls at the last nucleotide of exon 8 of the LAMA2 coding sequence, which is part of the consensus splice site for this exon. -

Merosin deficient congenital muscular dystrophy;C4748327:Muscular dystrophy, limb-girdle, autosomal recessive 23 Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Breda Genetics srl

Sep 30, 2020

The variant c.1206G>C (p.Gly402Gly) in the LAMA2 gene is reported as uncertain for laminin alpha 2-related dystrophy in ClinVar (Variation ID: 477438). The variant is reported with an estimated allele frequency of 0.000003985 in gnomAD exomes, with no homozygous individuals reported. The nucleotide position is highly conserved across 35 mammalian species (GERP RS: 6.06). This is a synonymous variant, which does not alter the amino acid sequence. Since the variant is located at the last nucleotide position of exon 8, it might have an impact on the splicing process (Human Splicing Finder – HSF 3.0 – predicts that the variant most probably affects splicing, altering the WT donor site). Gonorazky et al. (2019) reported the case of a proband with congenital muscular dystrophy 1A, who was compound heterozygote for a missense and a synonymous variant (c.4860G>A, p.Lys1620Lys) that falls on the last nucleotide of exon 33. The synonymous variant causes an exon-skipping event, that leads to a frameshift with stop-gain in exon 35. Overall, the LAMA2 expression was decreased (PMID: 30827497). Based on ACMG variant interpretation guidelines, we classify this variant as uncertain. However, based on the aforementioned evidence, there is a given likelihood that the variant may actually be pathogenic, even if we cannot exclude that it is a rare benign variant. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_noAF	Benign	-0.23
CADD	Uncertain	24
DANN	Benign	0.94

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	1.0
dbscSNV1_RF	Pathogenic	1.0
SpliceAI score (max)		0.66		Details are displayed if max score is > 0.2
DS_DG_spliceai		0.34		Position offset: 5
DS_DL_spliceai		0.66		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: rs1167723109; hg19: chr6-129475828;