Towards a Better Molecular Diagnosis of FMR1-Related Disorders-A Multiyear Experience from a Reference Lab.

The article summarizes over 20 years of experience of a reference lab in fragile X mental retardation 1 gene (FMR1) molecular analysis in the molecular diagnosis of fragile X spectrum disorders. This includes fragile X syndrome (FXS), fragile X-associated primary ovarian insufficiency (FXPOI) and fragile X-associated tremor/ataxia syndrome (FXTAS), which are three different clinical conditions with the same molecular background. They are all associated with an expansion of CGG repeats in the 5'UTR of FMR1 gene. Until 2016, the FMR1 gene was tested in 9185 individuals with the pre-screening PCR, supplemented with Southern blot analysis and/or Triplet Repeat Primed PCR based method. This approach allowed us to confirm the diagnosis of FXS, FXPOI FXTAS in 636/9131 (6.96%), 4/43 (9.3%) and 3/11 (27.3%) of the studied cases, respectively. Moreover, the FXS carrier status was established in 389 individuals. The technical aspect of the molecular analysis is very important in diagnosis of FXS-related disorders. The new methods were subsequently implemented in our laboratory. This allowed the significance of the Southern blot technique to be decreased until its complete withdrawal. Our experience points out the necessity of implementation of the GeneScan based methods to simplify the testing procedure as well as to obtain more information for the patient, especially if TP-PCR based methods are used.

[Non-invasive genetic prenatal diagnosis. Analysis of nucleic acids of foetal origin present in maternal vascular system].

Prenatal diagnosis is an important element of health care in pregnant women. Until now, prenatal testing of genetically determined diseases was invasive. Identification in maternal plasma of cell-free fetal nucleic acids (cffNA) has created new opportunities, and gave rise to genetic non-invasive prenatal diagnosis (NIPD). They are three leading trends in NIPD, depending on the clinical application: analysis of hereditary diseases, analysis of aneuploidy and study of maternal-fetal conflict. In case of hereditary diseases, application of NIPD is limited to autosomal dominant disorders where the mutation is carried on the paternal allelle. It refers to problems with distinguish fetal derived cell-free DNA from maternal cell-free DNA. The important issue for using NIPD techniques in practice is to develop appropriate law regulation. This is of particular importance in the non-medical applications, when the aim of testing could be e.g. selection of fetuses. The development of effective methods for the analysis of free fetal DNA present in the mother's bloodstream is a matter of few years and show the progress made in the fields of molecular biology and medicine. It seems that non-invasive testing for a wider range of genetic disorders is a only a question of time.