Síndrome de Hunter em pacientes amazonenses : proposta de alteração na estratégia diagnóstica e contribuição ao estudo da interferência de fatores epigenéticos na expressão do Gene IDS

Abstract

Hunter syndrome, or mucopolysaccharidosis II is one of the seven types of MPSs, lysosomal storage diseases inserted in the inborn errors of metabolism universe. Mutations in iduronate-2-sulfatase gene (IDS) cause deficiency of the homonymous enzyme activity and define the accumulation of GAG heparan and dermatan sulfate in the lysosomes, leading to dysfunction of cells, tissues and organs and clinical manifestations of wide phenotypic variety. The measures of the IDS gene expression in leukocytes by PCR in real time relative values evaluated by cDNA, were low in all five patients amazonenses in repeated tests, including in subjects with symptoms suggestive and no biochemical evidence. The partial sequencing of genomic DNA by choice of exon 9, home region of most mutations in Brazilian patients, to verify the presence of point mutation in all patients allowed to question the standard status gold of biochemical measurement of IDS enzyme for diagnosis. The use of PCR real time, via high-resolution melting analysis (HRM), proved to be useful for the identification of women with the mutant allele. Sequencing and HRM should be inserted in the flowchart for the confirmation of the disease with the accuracy of the advantages of early diagnosis and genetic counseling in more scientific basis. Plasma levels of manganese (Mn++) and B vitamins (pyridoxine and cobalamin) proved the deficiency of these items in patients and families, denouncing nutritional deficiency. Discusses the hypothesis that hipomanganesemia is directly related to low activity of IDS enzyme. The hypovitaminosis B6 and B12, in turn, can be related to hiperhomocistinemia / hypomethylation and changes in the methylation pattern of the IDS gene, further modifying gene expression and phenotypic defining multiple frames. This study advances the understanding of epigenetic accustomed processes to Hunter syndrome and justifies the development of new research in which a broader approach to validate low-cost therapeutic measures that are established in early childhood, pre-symptomatic, may prove to be able to modify the natural history of the disease to ensure greater efficiency of enzyme therapy and more favorable clinical outcome.