From dynamic FMR1 mutation to variable phenotypes: A case series from a large Tunisian family

Background: Fragile X messenger ribonucleoprotein 1 gene (FMR1) disorders result from a mutation in the FMR1 gene, leading to a deficiency or absence of the FMRP. Full mutations and premutations of the FMR1 gene are known to cause completely different symptoms. Aim: To determine the clinical phenotype of individuals with a full mutation or premutation of the FMR1 gene. Methods: We report 6 patients of the same Tunisian family with different clinical phenotypes. We gathered recent findings on the clinical spectrum of FMR1 mutations from 2020 to 2024 using PubMed, Google Scholar, ScienceDirect, and Web of Science. Results: Our observations revealed two first cousins, aged 4 and 13 years, respectively, with a medical history of recurrent infections. They exhibited developmental delay, hyperactivity, concentration difficulties, and autistic traits, with characteristic facial dysmorphia. Family investigation revealed a history of early menopause and primary ovary insufficiency diagnosis in their mothers and one aunt. The 79-year-old grandfather presented with recent memory and sleep disturbances, with signs suggestive of fragile X-associated tremor/ataxia syndrome (FXTAS) on brain MRI. The genetic assessment confirmed the fragile X syndrome (FXS) in children and the fragile X-associated primary ovarian insufficiency (FXPOI) in their mothers. Our search in literature uncovered a genetically diverse disorder exhibiting clinical variability influenced by factors such as gene size, methylation mosaicism, and the presence of premutations or full mutations, alongside various pathophysiological mechanisms. Conclusion: Clinical signs highlighted in our family report should alert clinicians to consider FXS, particularly facial dysmorphia and intellectual disability or language developmental delay, FXPOI for early menopause, and FXTAS for tremor and ataxia within the family context of FXS.