Genetic counseling and presymptomatic testing programs for Machado-Joseph Disease : lessons from Brazil and Portugal

Abstract

Machado-Joseph disease (MJD) is an autosomal dominant, late-onset neurological disorder and the most common form of spinocerebellar ataxia (SCA) worldwide. Diagnostic genetic testing is available to detect the disease-causing mutation by direct sizing of the CAG repeat tract in the ataxin 3 gene. Presymptomatic testing (PST) can be used to identify persons at risk of developing the disease. Genetic counseling provides patients with information about the disease, genetic risks, PST, and the decision-making process. In this study, we present the protocol used in PST for MJD and the relevant observations from two centers: Brazil (Porto Alegre) and Portugal (Porto). We provide a case report that illustrates the significant ethical and psychological issues related to PST in late-onset neurological disorders. In both centers, counseling and PST are performed by a multidisciplinary team, and genetic testing is conducted at the same institutions. From 1999 to 2012, 343 individuals sought PST in Porto Alegre; 263 (77%) of these individuals were from families with MJD. In Porto, 1,530 individuals sought PST between 1996 and 2013, but only 66 (4%) individuals were from families with MJD. In Brazil, approximately 50% of the people seeking PST eventually took the test and received their results, whereas 77% took the test in Portugal. In this case report, we highlight several issues that might be raised by the consultand and how the team can extract significant information. Literature about PST testing for MJD and other SCAs is scarce, and we hope this report will encourage similar studies and enable the implementation of PST protocols in other populations, mainly in Latin America.