[Heterogeneity of clinical characteristics of FMR1-related disorders]

The objective of this study is to provide a detailed description of clinical characteristics of disorders associated with FMR1 gene, which is located on the long arm of chromosome X. The most frequent FMR1 mutations are related to CGG-repeat expansion in the promoter region: premutation (from 55 to 199), full mutation (more than 200 repeats). The first section of the article is devoted to the fragile X mental retardation syndrome (FX syndrome) caused by FMR1 full mutation. The clinical characteristics of FX syndrome are presented. The second section provides information about specific phenotypes associated with FMR1 premutation that can be observed in maternal relatives (grandmother, mother's siblings, grandfather) of the child. The most frequent symptoms that observed in permutation carriers are mild cognitive impairment, ASD, ADHD in children, fragile X-associated tremor/ataxia syndrome (FXTAS) in older carries, fragile X-associated primary ovarian insufficiency (FXPOI) in women. The last section provides information about screening diagnostic instruments that help to identify the risk of fragile X syndrome. It also presents the key questions to be asked to family members in order to identify the risk of the permutation.