[Oculopharyngeal muscular dystrophy: study of patients from seven Spanish families with different GCG expansions in PABP2 gene]

Abstract

Introduction: Autosomal dominant oculopharyngeal muscular dystrophy (OPMD), with late onset due to ptosis and/or dysphagia, is caused by short (GCG)8-13 triplet-repeat expansions in the polyadenylation binding protein 2 (PABP2) gene, which is localized in chromosome 14q11. The severity of the dominant OPMD as well as the number of expansions that cause the disease are variable. (GCG)9 is mentioned as the most frequent and the genotype/phenotype has still not been well-determined.

Objective: To describe the type of expansions (GCG)n found in Spanish families with OPMD, establishing if there is variability of them and the possible geno-phenotypical correlations.

Methods: Clinicopathological and molecular studies have been performed in 15 consecutive patients, belonging to seven Spanish families with OPMD. The muscular biopsy study under electronmicroscopy shows intranuclear inclusions (INIs) in all the examined patients (one patient per family). The genetic findings confirm the cause of the disease in all the affected members and in one clinically asymptomatic member of one recently examined family: three families (six, one and one studied members, respectively) present the (GCG)9 expansion, two families (one studied member each one) present the (GCG)10 expansion and two families (one and four studied members respectively) present the (GCG)11 expansion. In these 15 patients with a short GCG expansion causing OPMD, clinical tests for OPMD and a follow-up study of their clinical course have been carefully assessed: in patients with the (GCG)9 expansion major abnormalities appeared in extrinsic ocular mobility and more precocious presentation of limb girld (lumbopelvic preferentially) weakness leading to a great disability before the seventh decade of life under the seventies in some patients and sometimes leading to death. In patients with (GCG)10 and (GCG)11 expansions, eye movements are always preserved and the limb girld muscles weakness did not appear before the seventh decade. No correlation seems to exist between age of onset of the ptosis or dysphagia and the different (GCG)n expansions and the surgical treatment of ptosis, performed in eight patients, showed good results independently of the (GCG)n mutation.

Conclusions: Although further clinical and genetic studies are necessary to establish a strict genotype/phenotype correlation in OPMD, we concluded that the (GCG)9 expansion involve more severe phenotypes than those related to the (GCG)10 or (GCG)11 expansions. Therefore, genetic testing could benefit prognosis in asymptomatic individuals.