High prevalence and phenotype-genotype correlations of limb girdle muscular dystrophy type 21 in Denmark

Objectives: The prevalence of limb girdle muscular dystrophy type 2I (LGMD2I) in northern Europe is unknown. We investigated this and the genotype-phenotype relation in LGMD2I. Methods: Prospective clinical and molecular screening of 118 Danish patients registered with LGMD was performed to divide patients into LGMD subtypes. Results: One hundred three patients fulfilled the clinical criteria for LGMD2. Thirty-eight had LGMD2I (27 homozygous, 11 compound heterozygolis for 826C > A), 23 had sarcoglycanopathy, 2 dysferlinopathy, 12 calpainopathy, and 4 Becker muscular dystrophy. The 24 patients with no molecular diagnosis did not harbor fukutin-related protein gene (FKRP) mutations. A clear clinical delineation was found between patients homozygous and compound heterozygous for the 826C > A mutation. Homozygous patients had later debut, milder clinical progression, and less muscle weakness compared with compound heterozygous patients, who were all wheelchair bound by their mid-20s. Impaired cardiac pump function was found in both groups. Interpretation: This study reports a different distribution of LGMD subtypes in Denmark than seen in other geographic regions, with a threefold to fourfold higher prevalence of LGMD2I than elsewhere. The findings support a clear clinical delineation between patients homozygous and compound hererozygous for the 826C > A mutation in FKRP. The findings suggest that, in the studied region, screening for the 826C > A mutation will identify all persons with LGMD2I.