Fragile X-associated tremor/ataxia syndrome

Niranjan N Singh MD (Dr. Singh of the University of Missouri - Columbia has no relevant financial relationships to disclose.)
Florian P Thomas MD MA PhD MS (Dr. Thomas, Chair, Department of Neurology, Seton Hall-Hackensack-Meridian School of Medicine, has no relevant financial relationships to disclose.)
Joseph Jankovic MD, editor. (Dr. Jankovic, Director of the Parkinson's Disease Center and Movement Disorders Clinic at Baylor College of Medicine, received research funding from Allergan, Allon, Ceregene, Chelsea, EMD Serono, Impax, Ipsen, Lundbeck, Medtronic, Merz, and Teva, and compensation for his services as a consultant or an advisory committee member by Allergan, Auspex, EMD Serono, Lundbeck, Merz, Neurocrine Biosciences, and Teva.)
Originally released September 25, 2004; last updated March 12, 2017; expires March 12, 2020

This article includes discussion of Fragile X-associated tremor/ataxia syndrome and FXTAS. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset triplet repeat disorder that leads to dementia, ataxia, tremor, and neuropathy. Its cause is a restricted triplet repeat expansion mutation in the fragile X mental retardation gene (FMR1), whereas a larger expansion results in fragile X syndrome A in children. Fragile X-associated tremor/ataxia syndrome affects less than 20% of female and about 50% of male carriers. In this article, the authors focus on fragile X-associated tremor/ataxia syndrome and its relation to fragile X syndrome A. Fragile X-associated tremor/ataxia syndrome illustrates the importance of obtaining a comprehensive family history that is not limited to clinical question of the patient in question. Fragile X-associated tremor/ataxia syndrome is in the differential diagnosis in patients with various combinations of the above symptoms with or without a family history of mental retardation. Some estimates suggest that as many as 1 in 3000 men above 50 years of age may develop fragile X-associated tremor/ataxia syndrome; such numbers would signify a great impact on healthcare costs. The pathomechanistic evidence of mitochondrial and RNA dysfunction and of a neurodevelopmental component to fragile X-associated tremor/ataxia syndrome is discussed.

Historical note and terminology

Researchers first began to look for a connection between fragile X syndrome A and the neurologic symptoms in elderly men when mothers of affected children noted that their children's grandfathers became forgetful, had frequent falls, and other neurologic problems. This resulted in the recognition of a syndrome originally referred to as “intention tremor, parkinsonism, and generalized brain atrophy in male carriers of a fragile X premutation” (Hagerman et al 2001).

In fragile X syndrome A, a cytosine-guanine-guanine (CGG) triplet repeat expansion in excess of 200 repeats leads to silencing of the FMR1 gene and its protein product, fragile X mental retardation protein, whereas fragile X-associated tremor/ataxia syndrome patients have a triplet repeat expansion of 55 to 200 CGG repeats.

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