Improved Genetic Testing Protocols Should be Available for Huntington’s Disease, Study Contends

Alice Melão avatar

by Alice Melão |

Share this article:

Share article via email
antidopaminergic meds and cognition

Adequate support and follow-up should be considered when implementing and designing pre-symptomatic genetic testing for Huntington’s disease, a study has revealed.

The study, “Perspectives on Genetic Testing and Return of Results from the First Cohort of Presymptomatically Tested Individuals At Risk of Huntington Disease,” was published in the Journal of Genetic Counseling.

Huntington’s disease is a genetic disorder characterized by the expansion of the CAG sequence in the HTT gene. The gene normally carries between 10 to 35 repeats of this small sequence. However, more than 36 repeats leads to the production of a longer version of the huntingtin protein.

Although this protein’s function is still unclear, its altered form causes brain cells to malfunction. Indeed, the number of HTT expansion repeats is inversely correlated with disease onset — the more repeats the earlier the disease will manifest.

Presymptomatic testing can be an important step for several disorders to promote preventive strategies and prompt treatments. However, it also may have a negative affect if associated with diseases without a cure, leading to loss of hope, major depression, and suicidal thoughts.

The genetic basis of Huntington’s was first described in 1983. Shortly after, tests were developed to assess the presence of associated genetic alterations and the probability of developing the disease.

This made Huntington’s one of the first diseases to be in the spotlight regarding the ethical and psychological issues related to pre-symptomatic genetic testing.

Johns Hopkins University researchers interviewed 39 individuals who had been enrolled in the Johns Hopkins Huntington’s disease pre-symptomatic testing protocol from 1986 to 1998. This study was one of the first two in which pre-symptomatic genetic testing for Huntington’s was implemented.

Fifteen participants were found to carry an HTT expanded version, 21 had HTT repeats within normal range, and three participants dropped out before test results were disclosed. Nine of the 15 participants with expanded repeats already had been clinically diagnosed with Huntington’s disease at the time of the interview.

The interviews were planned to discuss specific topics on the individuals’ testing experiences, reasons for testing, communication of test results, and affects of genetic testing on mental health, relationships, and life decisions. It also included a series of opinion questions about hypothetical scenarios, which involved the return of genetic test results and secondary findings following large-scale genetic testing.

“This qualitative study gathered opinions about genetic testing from people who received presymptomatic testing for Huntington’s disease 20-30 years ago and have lived with the implications of that testing for decades,” researchers wrote.

Most, but not all, participants shared the opinion that each individual should have the autonomy to decide whether and when to pursue Huntington’s disease genetic testing. Their answers were in line with typical practice and implemented guidelines in the fields of medical genetics and genetic counseling.

Also, this autonomy was perceived as a crucial aspect to what concerned the individual’s interest about being informed, or not, of potential secondary findings.

“This study presents the opinions of a unique and extremely well-informed [group of people] on issues that need to be taken into careful consideration by genetic counselors and other medical professionals,” researchers wrote.

Most participants expressed they were in favor of formal Huntington’s disease testing protocols that ensures counseling and follow-up visits. However, the majority opposed the idea that physicians could order a genetic test without passing through a formal protocol.

Also, participants refused the possibility that Huntington’s testing could be available by online direct-to-consumer methods.

“Exploration of more flexible and individualized options for testing and testing protocols that take an individual’s circumstances into account may be appropriate,” researchers added. “Nevertheless, careful consideration and more research are needed to properly evaluate these options and avoid adverse effects.”