[Neurodevelopmental (fragile X syndrome) and neurodegenerative (tremor/ataxia syndrome) disorders associated to the 'growth' of a gene]

AIM: To present the latest findings on fragile X syndrome, the first genetic disorder identified to be caused by a new type of mutation called trinucleotide repeat expansion.

DEVELOPMENT: Fragile X syndrome is the most common form of inherited mental retardation, is caused by hyperexpansion and hypermethylation of a CGG repeat tract in the FMR1 gene. In the first section we will discuss the various aspects of the gene mutation and the gene product, its phenotypic consequences in mutation carriers, diagnostic methodology, epidemiology, prevention, treatment and situation in Costa Rica. The second section deals with the recent findings in relation to the very recently described fragile X premutation tremor/ataxia syndrome, a neurodegenerative disorder affecting carriers of the mutation.

CONCLUSIONS: Screening for the gene premutation in aged individuals who have tremor and balance problems is important, especially when accompanied by other signs such as parkinsonism, short term memory loss and dementia. Family genetic counselling can help those affected as well as future generations which may inherit fragile X syndrome.