Estudo bioquímico e molecular da quitotriosidase em pacientes com Doença de Gaucher tipo 1 em Minas Gerais

Abstract

Gaucher disease (GD) is the most common lysosomal storage disease. It is caused by deficiency of the enzyme glucocerebrosidase, with accumulation of substrate in the lysosomes of the macrophages, mainly in the liver, spleen and bone marrow, which can affect the lungs, kidneys and central nervous system. The spectrum of disease is broad, but classically three types are recognized. The GD type 1 or non-neuronopathic form, is the most common form of the disease, with possibility of treatment with enzyme replacement therapy (ERT) or substrate reduction therapy (SRT). The chitotriosidase (ChT), a human chitinase, is 100 to 1,000 times higher than normal in patients with GD. The ChT activity decreases after initiation of therapy (ERT or SRT) and increases when it is stopped. Thus, their activity is useful for monitoring disease severity and effectiveness of treatment of patients with GD. However, the literature reports that approximately 6% of the population is homozygous for a duplication of 24 bp in exon 11 of CHIT1 (dup24) and does not produce ChT, which makes this enzyme useless in this case. Another 35% of the population is heterozygous for the mutation and produces only half the active enzyme. Thus, for the ChT can be used as a biochemical marker in patients with GD, it is essential that the CHIT1 genotype is known. In order to characterize molecular and biochemically the ChT in patients with GD type 1 in Minas Gerais state, a sample of 33 patients from Hospital das Clinicas (HC-UFMG) was studied, all under treatment, and compared with normal controls. The enzyme measurement assay was implemented and standardized at the Laboratory of Inborn Errors of Metabolism (HC-UFMG) and genotyping, performed at the Laboratory of Animal and Human Genetics (UFMG). In general, the ChT activity was 176 times higher in patients with GD type 1 than in healthy individuals. The result of genotyping revealed that 23 patients (70%) are homozygous normal (wt/wt), 7 (21%) heterozygous (wt/mut) and 3 (9%) were homozygous for dup24 (mut/mut). Three patients showed no correlation between dup24 genotype and ChT activity and, therefore, were tested for polymorphisms in CHIT1. Of these, two showed a polymorphism in exon 4 (G102S) while another had two polymorphisms in exon 11 (G354R and 4 pb deletion at the junction of exon/intron 11). This research was performed due the need for better monitoring of patients with GD type 1 in the HC-UFMG and the results show the ChT as useful marker for 82% of this population.