Merosin-deficient congenital muscular dystrophy type 1a: detection of LAMA2 variants in Vietnamese patients

Abstract

Background: Merosin-deficient congenital muscular dystrophy type 1A (MDC1A), also known as laminin-α2 chain-deficient congenital muscular dystrophy (LAMA2-MD), is an autosomal recessive disease caused by biallelic variants in the LAMA2 gene. In MDC1A, laminin- α2 chain expression is absent or significantly reduced, leading to some early-onset clinical symptoms including severe hypotonia, muscle weakness, skeletal deformity, non-ambulation, and respiratory insufficiency. Methods: Six patients from five unrelated Vietnamese families presenting with congenital muscular dystrophy were investigated. Targeted sequencing was performed in the five probands. Sanger sequencing was carried out in their families. Multiplex ligation-dependent probe amplification was performed in one family to examine an exon deletion. Results: Seven variants of the LAMA2 (NM_000426) gene were identified and classified as pathogenic/likely pathogenic variants using American College of Medical Genetics and Genomics criteria. Two of these variants were not reported in the literature, including c.7156-5_7157delinsT and c.8974_8975insTGAT. Sanger sequencing indicated their parents as carriers. The mothers of family 4 and family 5 were pregnant and a prenatal testing was performed. The results showed that the fetus of the family 4 only carries c.4717 + 5G>A in the heterozygous form, while the fetus of the family 5 carries compound heterozygous variants, including a deletion of exon 3 and c.4644C>A. Conclusion: Our findings not only identified the underlying genetic etiology for the patients, but also provided genetic counseling for the parents whenever they have an offspring.

Keywords: LAMA2 gene; MDC1A; Vietnamese; congenital muscular dystrophy; merosin-deficient congenital muscular dystrophy type 1A.

FIGURE 1

Distribution of pathogenicity of 836 unique LAMA2 variants and the effect of 465 pathogenic/likely pathogenic variants. The data was accessed in the LOVD database on 19 February 2023. VUS, variant of uncertain significance. Splice sites variants are alterations occurring at the start two nucleotides or the last two nucleotides of an intron.

FIGURE 2

Pedigrees of families 1-5 with variants in the LAMA2 gene. Probands are indicated by arrows. Affected individuals are shown in filled symbols. D: Deceased; y. o.: Year-old; TOP: Termination Of Pregnancy.

FIGURE 3

Sanger sequencing analysis of the variant c.8974_8975insTGAT in the family 3. Patient 3 carries variant c.8974_8975insTGAT (g.629283_629284insTGAT) in the homozygous state. The parents carry the variant in the heterozygous state. This variant creates a new stop codon at the position amino acid number 2995 (p.E2995*). The protein is truncated. Hom, homozygous; Het, heterozygous; WT, wild-type.

FIGURE 4

(A) Sanger sequencing analysis of the family 4. Patient 4 carried two variants, including c.7156–5_7157delinsT inherited from the father and c.4717 + 5G>A inherited from the mother. His sister and fetus only carried c.4717 + 5G>A in the heterozygous state. (B) Sequence comparison between wild type and variant c.7156-5_7157delinsT. The variant alters the sequence at the intersection of intron 50 and exon 51 and may produce a premature termination of the protein containing 2,386 amino acids (p.R2386*).

FIGURE 5

Sanger sequencing analysis and multiplex ligation-dependent probe amplification (MLPA) of the family of patient 5. Patient 5, his brother and the fetus carried compound heterozygous variants, including c.4644C>A (p.C1548*) inherited from the father (the left panel) and a deletion of exon 3 inherited from the mother (the right panel). Mut, mutation; Hom, homozygous; Het, heterozygous.

FIGURE 6

Location of the seven identified variants in the LAMA2 gene and protein. Deletion/insertion variant are shown in blue, nonsense variants in orange, and intron variants in green. Adapted to Zambon et al. (2020).