Clinical and genetic features of a large homogeneous cohort of oculopharyngeal muscular dystrophy patients from the Canary Islands

Background: Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant, late-onset myopathy characterized by ptosis, dysphagia, and progressive proximal limb muscle weakness. The disease is produced by a short expansion of the (GCN)_n triplet in the PABPN1 gene. The size of expansion has been correlated to the disease onset and severity. We report the clinical features of a large cohort of OPMD patients harboring the (GCN)15 allele from the Canary Islands.

Methods: A retrospective observational study was performed analyzing the clinical, demographic, and genetic data of 123 OPMD patients. Clinical data from this cohort were compared with clinical data collected in a large European study including 139 OPMD patients.

Results: A total of 113 patients (94.2%) carried the (GCN)15 expanded PABN1 allele. Age of symptoms' onset was 45.1 years. The most frequent symptom at onset was ptosis (85.2%) followed by dysphagia (12%). The severity of the disease was milder in the Canary cohort compared to European patients as limb weakness (35.1% vs. 50.4%), the proportion of patients that require assistance for walking or use a wheelchair (9.3% vs. 27.4%), and needed of surgery because of severe dysphagia (4.6% vs. 22.8%) was higher in the European cohort.

Conclusions: Nearly 95% of patients with OPMD from the Canary Islands harbored the (GCN)15 expanded allele supporting a potential founder effect. Disease progression seemed to be milder in the (GCN)15 OPMD Canary cohort than in other cohorts with shorter expansions suggesting that other factors, apart from the expansion size, could be involved in the progression of the disease.