Children with fragile X syndrome (FXS) inherit the mutation from their mothers, almost all of whom carry the premutation - defined as 55 - 200 CGG repeats in the FMR1 gene. Premutation carrier mothers have participated in clinical studies and have been reported to suffer from elevated risk of motor, neurocognitive, health, and psychiatric symptoms, although there is controversy regarding whether these symptoms are primary characteristics of the premutation phenotype. Alternatively, the symptoms could emanate from stressful parenting for a child with full mutation FXS. This application proposes research that will advance understanding of the FMR1 premutation phenotype, conducted by Drs. Marsha Mailick, Jan S. Greenberg, Leann Smith, Elizabeth Berry-Kravis, and Murray Brilliant from the University of Wisconsin-Madison Waisman Center, Marshfield Clinic Research Foundation, and Rush University Medical Center. The project will characterize the FMR1 premutation phenotype by studying 344 women: (1) 144 women drawn from a 20,000-person population-based sample who constitute the Personalized Medicine Research Project (PMRP) of the Marshfield Clinic, of whom 72 are premutation carriers (who have between 55 and 190 CGG expansions) but are unaware of their genotype and do not have children with diagnosed FXS, and 72 are matched controls (< 41 CGG repeats); and (2) 200 premutation carrier mothers of full mutation children with FXS who are participating in our ongoing studies and clinics. To the best of our knowledge, this is the first study designed to include both a population-based sample of women with the premutation who were not reverse-ascertained from a child with full-mutation FXS as well as clinically- ascertained women with the premutation. Thus, it offers the opportunity to determine whether the phenotypic characteristics of the premutation carrier mothers of full mutation children with FXS are representative of the full range of carriers in the population.
Our Specific Aims are: (1) Define the motor, neurocognitive, health, and psychiatric phenotypes of female premutation carriers in a population-based sample (not confounded by knowledge of their genotype or parenting a child with FXS) and determine how the phenotype differs in a clinically-ascertained sample; (2) Determine the effect of stress exposure on the phenotype of FMR1 premutation carriers; and (3) Identify the age-related profile of symptoms in premutation carriers.. Additionally, we will incorporate the genotype of the FMR1 premutation into the analyses (CGG repeat length, activation ratio, and AGG number and location) to determine genotype-phenotype correlations and gene-by-environment interactions in predicting the phenotype. We have assembled an exceptionally strong interdisciplinary team of scientists including those with expertise in biostatistics, cognitive and developmental psychology, epidemiology, genetics, neurology, pediatrics, psychoneuroendocrinology, and social science to carry out these Aims.
The public health relevance of the proposed study rests on four factors: (1) the population prevalence of FMR1 CGG repeats in the premutation range, which is sufficiently high to have public health implications, (2) the importance of determining the extent and severity of the clinical manifestations of the premutation in a population-based sample, (3) the opportunity to compare the phenotype in population-based versus clinically- ascertained samples of female carriers, and thus to separate the toll of stressful parenting and knowledge of one's genetic status from the primary effect of the premutation itself, and (4) the need to understand factors associated with the heterogeneity of the premutation phenotype, given the resilience of some carriers and the vulnerability of others.
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