[Triplet expansion cytosine-guanine-guanine: Three cases of OMIM syndrome in the same family].

INTRODUCTION

The dynamic increase in the number of triplet repeats of cytosine-guanine-guanine (CGG) in the FMR1 gene mutation is responsible for three OMIM syndromes with a distinct clinical phenotype: Fragile X syndrome (FXS) and two pathologies in adult carriers of the premutation (55-200 CGG repeats): Primary ovarian insufficiency (FXPOI) and tremor-ataxia syndrome (FXTAS) associated with FXS.

CLINICAL OBSERVATION AND METHODS

CGG mutation dynamics of the FMR1 gene were studied in DNA samples from peripheral blood from the index case and other relatives of first, second and third degree by TP-PCR, and the percentage methylation.

RESULTS

Diagnosis of FXS was confirmed in three patients (21.4%), eight patients (57.1%) were confirmed in the premutation range transmitters, one male patient with full mutation/permutation mosaicism (7.1%) and two patients (14.3%) with normal study. Of the eight permutated patients, three had FXPOI and one male patient had FXTAS.

DISCUSSION

Our study suggests the importance of making an early diagnosis of SXF in order to carry out a family study and genetic counselling, which allow the identification of new cases or premutated patients with FMR1 gene- associated syndromes (FXTAS, FXPOI).