GRN Gene & FTD | Understanding the Basque Mutation Impact

Genetic Inheritance and the Onset of FTD

Rosa and Carmen Rivoira learned their future held a specific, irreversible challenge shortly after their mother, Argentine artist Eugenia Streb, received a diagnosis of frontotemporal dementia. Genetic testing confirmed that both sisters carry the mutant GRN gene. This specific mutation follows an autosomal dominant inheritance pattern, meaning each child of a carrier faces a 50% chance of inheriting the risk. Nahuel Magrath, a neuropsychiatrist and director of the Fleni Frontotemporal Dementia Clinic in Argentina, oversees the medical support for the family as they navigate the implications of this news.

Genes function as internal instruction manuals for cellular operations. The GRN gene, located on chromosome 17, remains critical for producing progranulin, a protein required for healthy brain function. A mutation in this gene can reduce or eliminate the production of this essential protein. This physiological deficit triggers frontotemporal dementia, a disease targeting the frontal and temporal lobes. These areas manage impulse control, movement, personality, language, and empathy. Patients often exhibit sudden behavioral shifts, such as public disinhibition or total neglect of daily tasks, because their brain loses its ability to regulate these functions.

The Search for Answers and the Failure of Clinical Trials

Frontotemporal dementia lacks a cure or established treatment options. Jennifer Yokoyama, a neurogeneticist at the University of California, San Francisco, notes that pathogenic variants of the GRN gene account for approximately 5% of all frontotemporal dementia cases and roughly 20% of cases where a family history is present. The Rivoira sisters participated in an international protocol associated with the pharmaceutical company Alector, which tested the drug latozinemab in a phase 3 trial. The trial aimed to slow disease progression, but the drug failed to meet its primary clinical endpoint, leading to its cancellation.

For the sisters, the diagnosis introduces a permanent, unspoken tension. They estimate that thirty-five years remain before they reach the age of likely symptom onset. This timeframe hangs over their major life decisions, including whether to pursue pregnancy naturally or utilize preimplantation genetic diagnosis to avoid passing the mutation to the next generation. Meanwhile, their mother’s decline has progressed, forcing the family to observe the erosion of an artist who once found solace in her work but later lost the ability to execute her vision.

Tracing the Origin of the Basque Mutation

Neurologists investigating the family history of Eugenia Streb eventually pointed to the Mugarza lineage and its Basque roots. Fermín Moreno, a neurologist at Donostia University Hospital in Spain, tracks 18 families in Gipuzkoa province who carry what researchers identify as the Basque mutation of frontotemporal dementia. While the region does not represent a perfectly isolated genetic population, centuries of endogamous marriage patterns preserved specific mutations within local family lines. These disparate families likely trace their history to a single common ancestor who carried the mutation long before modern diagnostics existed.

Today, life in the Rivoira household revolves around the logistical requirements of care. Specialized caregivers now assist with physical transfers and emotional stabilization. The family environment remains anchored by the physical objects of a long life, such as childhood portraits and books, but the shadow of the genetic condition is never absent. Carmen Rivoira describes the initial period of grief and the receipt of her own test results as a paralyzing experience. She notes that navigating life in her thirties is difficult enough without the constant presence of a looming, genetically predetermined future.