Genotype-Phenotype Relationships in Fragile X Families

PROJECT SUMMARY The neurodegenerative disorder, fragile X-associated tremor/ataxia syndrome (FXTAS), initially described by us in 2001, is still considered a male-dominant disorder, with the second, normal X chromosome in females diminishing neuronal toxicity of the premutation (55 to 200 CGG repeats). Women with FXTAS do have lower penetrance and less severe tremor and ataxia compared to men; however, against expectations for an X- linked disorder, females with FXTAS have the preponderance of neuropsychiatric problems, which include pain symptoms and anxiety, and immune/inflammatory involvement. Our principal objective for the next project period is to characterize the preFXTAS and FXTAS phenotypes in women compared to men and to assess the role of neuropsychiatric and autoimmune problems and their molecular underpinnings in the initiation and progression of FXTAS. Our central hypothesis is that the RNA-toxicity mechanism that underlies the male- predominant motor dysfunction in FXTAS also drives the well-known susceptibility of females to develop both psychiatric and immune-related problems. We hypothesize that RNA toxicity and consequent enhanced reactive oxygen species (ROS) generation are likely to amplify the intrinsic pro-inflammatory state in females, particularly in those females with pain, where IL6 and TNFα are generally enhanced. During the proposed project period, we will assess the role of autoimmune, neuropsychiatric, and pain disorders in women with preFXTAS and FXTAS and determine how this relates to the development and progression of FXTAS. The clinical phenotype including MRI studies will be assessed under Aim 1. The molecular aspects of these mechanisms will be addressed under Aim 2. Under Aim 3, we will carry out a detailed correlation analysis of the interrelationship between the clinical features, their possible molecular underpinnings, and their roles on rates of progression and severity of FXTAS in males and females. In addition, under Aim 3, we will provide an initial assessment of the relationship between the clinical features of FXTAS and comorbid conditions, such as parkinsonism, that are common in carriers. Thus, our ongoing Genotype-Phenotype project will continue to follow the largest known clinical cohort of premutation carriers with FXTAS, focusing particularly on females for whom knowledge of phenotypes is more limited. Progression will be assessed every two years through evaluation of various clinical domains, including medical and neurological testing, quantitative motor testing of tremor and ataxia, neuropsychological testing of executive function and memory, psychiatric evaluation, and MRI studies. For each of these clinical domains, progression of symptoms and pathology are quantified; our preliminary data show that while males progress twice as fast as females in motor dysfunction, females have twice the penetrance of psychopathology and progress faster in anxiety and depression. Such data will lead to a better understanding of the natural history of FXTAS in both females and males, and such quantification efforts will lead to improved outcome measures for future clinical trials and earlier treatments.