[Private mutations in the myophosphorylase gene: the first case in a patient of Latin American descent].

Introduction: McArdle's disease (glycogenoses type V) is a common metabolic myopathy caused by deficient myophosphorylase activity. The disease is due to mutations in the myophosphorylase (PYGM) gene and is present in a large number of countries.
Case Report: A 13-year-old male who suffered an episode of muscle pain and offered increased levels of creatinkinase in plasma, myoglobinuria and mild weakness of the proximal muscles, after short but vigorous exercise. The patient was born in Ecuador and was adopted by a Spanish family. The myophosphorylase gene was analysed completely and the patient was found to be a carrier of a missense mutation, a homozygous change where a G is replaced by an A in exon 11, changing a valine for a methionine in codon 456 (V456M). The mutation described above affects an amino acid that is conserved in the enzyme and which was not present in the control population that was studied.
Conclusions: These findings show the presence of McArdle's disease in several ethnic groups and confirm that the ethnic origin of the patient is important when it comes to deciding what mutations should be analysed first in molecular diagnosis studies.