Genomic screening for beta-sarcoglycan gene mutations: missense mutations may cause severe limb-girdle muscular dystrophy type 2E (LGMD 2E) |
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Authors: | Bonnemann CG; Passos-Bueno MR; McNally EM; Vainzof M; de Sa Moreira E; Marie SK; Pavanello RC; Noguchi S; Ozawa E; Zatz M; Kunkel LM |
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Institution: | Howard Hughes Medical Institute, Boston, MA, USA. |
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Abstract: | Autosomal recessive limb-girdle muscular dystrophies (LGMDs) are
genetically heterogeneous. A subgroup of these disorders is caused by
mutations in the dystrophin-associated sarcoglycan complex. Truncating
mutations in the 43 kDa beta-sarcoglycan gene (LGMD 2E) were originally
identified in a sporadic case of Duchenne-like muscular dystrophy, and a
common missense mutation (T151R) was identified independently in Indiana
Amish pedigrees with a milder form of LGMD. To facilitate mutational
analysis of larger numbers of patients directly from genomic DNA, as
opposed to reverse transcribed RNA from muscle biopsies, we have determined
the genomic structure of the beta-sarcoglycan gene. The open reading frame
of the beta-sarcoglycan coding region extends over six exons. Primers were
designed for PCR amplification of single exons from genomic DNA and
subsequent single strand conformation polymorphism (SSCP) analysis. We
screened 15 patients from the Brazilian LGMD patient population, 13 of whom
followed a severe course. Most of the patients had been assessed previously
for deficiency of alpha- sarcoglycan immunofluorescence on muscle biopsy
sections as a marker for disease of the sarcoglycan complex. Novel
mutations in two familial and two sporadic cases of severe childhood-onset
LGMD were identified. Only one of these patients carried a truncating
mutation (homozygous 2 bp deletion, FS164TER), while the other three
carried missense mutations (homozygous R91P, homozygous M100K, heterozygous
recessive L108R; only one allele could be identified in this family). All
three missense mutations occurred in exon 3, coding for the immediate
extracellular domain. Complete absence for all three of the known
sarcoglycans was noted by immunohistochemistry on muscle biopsy sections of
the patients.
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