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D. Rivera, L. Garnica - Hyashi, A. Nava - Castañeda, H. Mejia-Lopez, C. Villanueva-Mendoza, J. C. Zenteno; (GCG)11 Genotype Is Associated to an Earlier Onset of Oculpharingeal Muscular Dystrophy in Mexican Population. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3126.
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Oculopharingeal muscular dystrophy (OPMD) is a muscular dystrophy caused by mutations in the PABPN1 gene, specifically triplet expansions of GCG in the first exon, from a normal number of 6 to an abnormal number of 8 to 13 triplets. The disease is transmitted as an autosomal dominant trait and the main clinical features are adult onset ptosis, dysphagia and limb weakness. Several studies have been failed to identify a genotype - phenotype correlation in OPMD. In this work we describe a statistically significant earlier onset of the disease in patients with (GCG)11 genotype compared with (GCG)9 genotype, these are the only two genotypes described in Mexican population with OPMD to date.
Twenty two patients from different Mexican unrelated families with a molecular confirmed diagnosis of OPMD were included. Signs and symptoms and their age of onset were recorded for each patient. The molecular analysis consisted in PCR amplification and allele specific sequencing of the PABPN1 gene exon 1. Two groups, the (GCG)11 and (GCG)9 genotype were identified and their age of onset was compared by using a T- test.
Of a total of 22 patients, 15 (68%) showed a (GCG)11 expanded allele while the remaining 7 (32%) had a (GCG)9 expanded allele. In all patients the wild type allele was (GCG)6. Of the 15 (GCG)11 cases, two had dysphagia as the presenting symptom, and the other 13 had ptosis as the presenting symptom. In the (GCG)9 group, 5 had ptosis and 2 had dysphagia as the initial symptom.The mean age of presentation was 46.5 years for the (GCG)11 group and 54.7 years for the (GCG)9. When comparing onset ages with T-test, a statistically significant difference was noted with a p<0.05. These results indicate an earlier onset of symptoms in the (GCG)11 group when compared with the (GCG)9 group.
In Mexican population with OPMD, the (GCG)11 genotype confers an earlier onset of the disease than genotype (GCG)9. This data contributes to the knowledge of the genotype - phenotype correlation in OPMD. More studies in different populations and with different types of mutations are needed to completely describe the correlation in the number of expanded triplets and the clinical spectrum of OPMD.
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