Ethical Dilemmas in Predictive Testing for Monozygotic Twins With Hereditary ALS: A Clinical Case Report

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder typically presenting in midlife and leading to death within 2-5 years of onset. Pathogenic SOD1 variants, inherited in an autosomal dominant manner, account for approximately 20% of hereditary ALS cases. Predictive genetic testing in SOD1-related ALS presents unique ethical challenges, particularly in monozygotic twins who share identical genetic information but hold differing views about testing. We describe an 18-year-old monozygotic twin who requested predictive testing for the familial SOD1 pathogenic variant identified in her father, who died from ALS at age 40. This conferred a 50% a priori risk to both twins. One twin had long expressed the desire to know her genetic status, while the other preferred not to pursue testing. Because a positive result in one twin would automatically reveal the status of the other, the case raised ethical tensions surrounding autonomy, beneficence, non-maleficence, and justice. Institutional ethics consultation and peer supervision were used to navigate these competing ethical imperatives and provided initial recommendations and direction. Additional valuable insights were gained through a peer-supervision framework that brought together genetic counselors across varying levels of experience and specialties. These discussions informed our ethical assessment and supported the decision to proceed with predictive testing, as the benefits were ultimately deemed to outweigh the potential risks. Testing identified the familial SOD1 pathogenic variant, which was disclosed to the patient and her family. Her twin subsequently elected to undergo confirmatory testing and received comprehensive genetic counseling and psychosocial support. Ethical complexities surrounding predictive genetic testing in monozygotic twins with hereditary neurodegenerative diseases, such as ALS, require careful balancing of autonomy, beneficence, non-maleficence, and justice. Structured peer supervision is essential for working through ethical uncertainty, guiding sound clinical decisions, and supporting patient-centered care.