Objective: Characterize genetically a series of cases of patients with Huntington’s disease and their family members at risk in the city of Manaus, capital of the Amazonas state.

Background: Huntington’s disease (HD) is a genetic disease with an autosomal dominant inheritance pattern. Despite the importance of HD and its impact on public health, there were no genetic studies performed in the Brazilian Amazonian population.

Method: The participants were from a reference center for movement disorders in Manaus, Amazonas. All patients clinically diagnosed with HD attended from 2010 until 2019. Their relatives at risk were invited to participate. Demographic and clinical data were obtained from medical records. Peripheral blood was collected for DNA extraction. Amplification of CAG repeats in the HTT gene was performed using fluorescently labeled primers. The size of PCR fragments was analyzed by capillary electrophoresis in an automatic sequencer.

Results: We tested a total of 45 individuals. We found 33 carriers of an expanded allele, 26 patients clinically diagnosed with HD, and 7 individuals at risk (presymptomatic). The CAG length varied from 39 to 76 in expanded alleles (mean = 46.6 ± 8.0). In clinically diagnosed patients, age at onset varied from 25 to 57 years old (mean = 35.6 ± 8.7). Also, a negative correlation was found between CAG length and age at onset (Pearson coefficient: -0.6). Disease duration varied from 1 to 25 years (mean = 11.4 ± 7.9). Two cases manifested symptoms with age below 20 years (Juvenile HD). We found paternal inheritance in 71% of the cases and maternal inheritance, in the other 29%. Furthermore, only 6% of the families of HD carriers were from the state of Amazonas.

Conclusion: Measures of central tendency and dispersion were within the range of previous studies. However, the mean values of the age of onset was a little lower than in most of the other studies, and we have not observed the bias toward paternal transmission previously. Furthermore, our data indicate that Amazonas was not a place where immigrant carriers of HD mutation settled at first, but rather that the HD mutation is spreading from other Brazilian regions to this state.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/genetic-analysis-of-huntingtons-disease-in-a-brazilian-amazonian-population/