Reviewing large LAMA2 deletions and duplications in congenital muscular dystrophy patients

Abstract

Background: Congenital muscular dystrophy (CMD) type 1A (MDC1A) is caused by recessive mutations in laminin-2 (LAMA2) gene. Laminin-211, a heterotrimeric glycoprotein that contains the 2 chain, is crucial for muscle stability establishing a bond between the sarcolemma and the extracellular matrix. More than 215 mutations are listed in the locus specific database (LSDB) for LAMA2 gene (May 2014). Objective: A limited number of large deletions/duplications have been reported in LAMA2. Our main objective was the identification of additional large rearrangements in LAMA2 found in CMD patients and a systematic review of cases in the literature and LSDB. Methods: In four of the fifty-two patients studied over the last 10 years, only one heterozygous mutation was identified, after sequencing and screening for a frequent LAMA2 deletion. Initial screening of large mutations was performed by multiplex ligation-dependent probe application (MLPA). Further characterization implied several techniques: long-range PCR, cDNA and Southern-blot analysis. Results: Three novel large deletions in LAMA2 and the first pathogenic large duplication were successfully identified, allowing a definitive molecular diagnosis, carrier screening and prenatal diagnosis. A total of fifteen deletions and two duplications previously reported were also reviewed. Two possible mutational “hotspots” for deletions may exist, the first encompassing exons 3 and 4 and second in the 3’ region (exons 56 to 65) of LAMA2. Conclusions: Our findings show that this type of mutation is fairly frequent (18.4% of mutated alleles) and is underestimated in the literature. It is important to include the screening of large deletions/duplications as part of the genetic diagnosis strategy.