title: Mutations in LAMA2 and CAPN3 genes associated with genetic and phenotypic heterogeneities within a single consanguineous family involving both congenital and progressive muscular dystrophies.
abstract: LGMD (limb-girdle muscular dystrophy) and CMD (congenital muscular dystrophy) are two common forms of neuromuscular disorders which are distinguishable by their age of onset but with probably a similar underlying pathway. In the present study, we report immunohistochemical, Western-blot and genetic analyses in a large consanguineous Tunisian family with two branches, including seven patients sharing similar LGMD2 phenotype in one branch and one CMD patient in the other branch. Linkage analyses were compatible with the LGMD2A locus in one branch and the MDC1A (muscular dystrophy congenital type 1A) locus in the other branch. This result was supported by deficiency in merosin and calpain3 in the CMD patient and LGMD patients respectively. Mutation analysis revealed two distinct mutations: a c.8005delT frameshift deletion in exon 56 of the LAMA2 (laminin-α2) gene (MDC1A) was found in the CMD patient and a new homozygous mutation c.1536+1G>T in the donor splice site of intron 12 of the CAPN3 (calpain3) gene (LGMD2A) was found in the LGMD patients. RT-PCR (reverse transcription-PCR) performed on total RNA from a LGMD2A patient's muscle biopsy showed complete retention of intron 12 in CAPN3 cDNA, generating a PTC (premature termination codon) that potentially elicits degradation of the nonsense mRNA by NMD (nonsense-mediated mRNA decay). Our results indicate that mRNA analysis is necessary to clarify the primary effect of genomic mutations on splicing efficiency that alters mRNA processing and expression level.
authors.affiliation: Laboratoire de Génétique Moléculaire Humaine, Faculté de Médecine de Sfax, Sfax, Tunisia. ikhlasshadj@gmail.com
authors.forename: Ikhlass
authors.initials: I
authors.lastname: Hadj Salem
authors.forename: Fatma
authors.initials: F
authors.lastname: Kamoun
authors.forename: Nacim
authors.initials: N
authors.lastname: Louhichi
authors.forename: Souad
authors.initials: S
authors.lastname: Rouis
authors.forename: Mariam
authors.initials: M
authors.lastname: Mziou
authors.forename: Nourhene
authors.initials: N
authors.lastname: Fendri-Kriaa
authors.forename: Fatma
authors.initials: F
authors.lastname: Makni-Ayadi
authors.forename: Chahnez
authors.initials: C
authors.lastname: Triki
authors.forename: Faiza
authors.initials: F
authors.lastname: Fakhfakh
mesh_terms: D001483:Base Sequence; D015153:Blotting, Western; D002154:Calpain / Q000235:genetics*; D002874:Chromosome Mapping; D018389:Codon, Nonsense / Q000235:genetics; D003241:Consanguinity; D004252:DNA Mutational Analysis; D005190:Family; D005260:Female; D018740:Genetic Heterogeneity; D008040:Genetic Linkage; D006801:Humans; D007797:Laminin / Q000235:genetics*; D008297:Male; D009124:Muscle Proteins / Q000235:genetics*; D009136:Muscular Dystrophies / Q000235:genetics; D049288:Muscular Dystrophies, Limb-Girdle / Q000235:genetics*; D020871:RNA Stability; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017423:Sequence Analysis, RNA; D014416:Tunisia
chemical_list: D018389:Codon, Nonsense; D007797:Laminin; D009124:Muscle Proteins; D012333:RNA, Messenger; C102645:laminin alpha 2; C105884:CAPN3 protein, human; D002154:Calpain