Objective: To compare the 15 years cumulative incidence of cancer (CIC) and the proportion of cancer as a cause of death in symptomatic Spinocerebellar ataxia type 3 /Machado Joseph disease (SCA3/MJD) carriers with those observed in controls.

Background: Polyglutamine diseases have been related to a reduced risk for cancer. This association was not studied in SCA3/MJD yet.

Methods: SCA3/MJD individuals belonging to the Rio Grande do Sul cohort from 2000 to 2015 were identified. A structured interview was done with affected individuals and with unrelated controls. CIC as published by the National Institute of Cancer (INCA), Brazil, was used as a population control. Causes of death among SCA3/MJD families and paired unrelated controls were also obtained from the Public Information System on Mortality.

Results: 154 SCA3/MJD patients and 80 unrelated controls were interviewed. CIC were 7/154 (4.5%) and 5/80 (6.3%) among SCA3/MJD and unrelated control individuals, respectively. For an absolute risk reduction of 1.8 between cases and controls, 1,938 individuals per group would be needed to detect a significant difference between groups. Since the total symptomatic SCA3/MJD population equaled 625 individuals in 2015, this study was interrupted. Cancer was a cause of death in 9/101 (8.9%) SCA3/MJD and in 52/202 (26.2%) controls, with an absolute reduction risk of 17.3% in the SCA3/MJD group (χ²=12.421; p=0.001; OR 0.27, 95%CI 0.13 to 0.58).

Conclusions: Due to the rarity of SCA3/MJD, CIC studies with statistical power are unfeasible. However, we detected a significant reduction of cancer as a cause of death in SCA3/MJD.

International MJD Conference, 24th to 29th August 2015, in Cairns, Australia.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/cancer-in-machado-joseph-disease-patients-low-frequency-as-a-cause-of-death/