Molecular diagnosis of Huntington's disease in Trinidadian families via triplet repeat primed PCR, fragment analysis, and nanopore sequencing

BackgroundHuntington's disease (HD) is a neurodegenerative disorder caused by CAG expansions in the Huntingtin (<i>HTT</i>) gene. Due to its non-specific and variable phenotype, diagnosis requires clinical assessments and genetic testing. In the Caribbean, the genetic etiology of HD is underexplored due to the unavailability of genetic testing.ObjectiveWe investigated whether 32 participants from four multigenerational families from Trinidad and Tobago (T&T) presenting with Huntington-like symptoms carried <i>HTT</i> CAG expansions, and whether CAG length was related to decreasing age of onset with each generation.MethodsParticipants were genotyped using triplet repeat primed PCR followed by previously-established fragment analysis and a nanopore sequencing based method with a custom bioinformatics workflow.ResultsAll symptomatic participants carried <i>HTT</i> CAG expansions (42-57 CAGs), confirming HD. Among participants aged 20-65 years (n = 24), clinical and genetic diagnoses were concordant for 22 participants (13 symptomatic with 42-57 CAGs, and nine asymptomatic with 13-27 CAGs). Two asymptomatic participants aged 22 and 43 years carried 46-47 and 37-39 CAGs, respectively. Among eight participants <18 years, one symptomatic 16-year-old carried 49-50 CAGs, and seven are currently asymptomatic (three with 50-52 CAGs, and four with 14-17 CAGs). In three families, decreasing age of onset and increasing CAG length were observed in each successive generation. Methods were highly correlated (R² = 0.998).ConclusionsWe demonstrated the application of nanopore sequencing with a custom bioinformatics workflow to estimate the size of <i>HTT</i> CAG repeats. This is the first genetic report of HD in T&T, among limited records in the Caribbean.