Sarcoglycanopathies are responsible for 68% of severe autosomal recessive limb-girdle muscular dystrophy in the Brazilian population.
Sarcoglycanopathies (SGPs) constitute a subgroup of limb-girdle muscular dystrophies (LGMD), where the primary defect in one sarcoglycan (SG) glycoprotein (alpha-SG, beta-SG, gamma-SG or delta-SG) results in a deficiency of the whole complex. Four genes, at 17q, 4q, 13q and 5q, encode the four glycoproteins, and mutations in these genes cause diseases called LGMD2D, 2E, 2C and 2F. To estimate the prevalence, relative proportions and clinical features of SGPs, we have studied the SG proteins in muscle biopsies of 140 patients (from 115 unrelated Brazilian families) with a clinical diagnosis of LGMD. Alpha-SG immunofluorescence analysis showed a positive staining pattern in 70% (80/115) of the families, a patchy pattern in 14% (16/115) and a negative pattern in 16% (19/115) of the families. All the 19 alpha-SG negative, and four of the 16 alpha-SG patchy patients were also deficient for the other three SG proteins, confirming the diagnosis of SGP in 20% of the LGMD families. None of the positive alpha-SG patients were deficient for any of the other three SG proteins, supporting the view that the SG complex functions as a unit. DNA analysis for the four sarcoglycan genes showed that alpha-SG mutations accounted for 47%, beta-SG for 16%, gamma-SG for 16% and delta-SG for 21% of the cases. SG abnormalities were observed in only 8.5% of patients with milder LGMD forms, but were present in 68% of patients with a severe Duchenne-like course. The relatively high frequency of SGP among Brazilian people with LGMD may be due to the disproportionally high frequency of African Brazilian SGP patients with the same mutation (particularly among LGMD2C and 2F patients), suggesting a founder effect. Consanguinity is also common in our SGP families.[1]References
- Sarcoglycanopathies are responsible for 68% of severe autosomal recessive limb-girdle muscular dystrophy in the Brazilian population. Vainzof, M., Passos-Bueno, M.R., Pavanello, R.C., Marie, S.K., Oliveira, A.S., Zatz, M. J. Neurol. Sci. (1999) [Pubmed]
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