Elevated Fmr1 mRNA levels and reduced protein expression in a mouse model with an unmethylated Fragile X full mutation.

The human FMR1 gene contains a CGG repeat in its 5' untranslated region. The repeat length in the normal population is polymorphic (5-55 CGG repeats). Lengths beyond 200 CGGs (full mutation) result in the absence of the FMR1 gene product, FMRP, through abnormal methylation and gene silencing. This causes Fragile X syndrome, the most common inherited form of mental retardation. Elderly carriers of the premutation, defined as a repeat length between 55 and 200 CGGs, can develop a progressive neurodegenerative syndrome: Fragile X-associated tremor/ataxia syndrome (FXTAS). In FXTAS, FMR1 mRNA levels are elevated and it has been hypothesised that FXTAS is caused by a pathogenic RNA gain-of-function mechanism. We have developed a knock in mouse model carrying an expanded CGG repeat (98 repeats), which shows repeat instability and displays biochemical, phenotypic and neuropathological characteristics of FXTAS. Here, we report further repeat instability, up to 230 CGGs. An expansion bias was observed, with the largest expansion being 43 CGG units and the largest contraction 80 CGG repeats. In humans, this length would be considered a full mutation and would be expected to result in gene silencing. Mice carrying long repeats ( approximately 230 CGGs) display elevated mRNA levels and decreased FMRP levels, but absence of abnormal methylation, suggesting that modelling the Fragile X full mutation in mice requires additional repeats or other genetic manipulation.

Genetic and clinical analysis of a large Dutch Gilles de la Tourette family.

Gilles de la Tourette syndrome is a complex neuropsychiatric disorder, which becomes evident in childhood between the ages of 2 and 15 years. Tourette syndrome is defined by the occurrence of a large range and variable number of unwanted repetitive simple or complex motor and vocal tics that start in childhood and follow a waxing and waning course. A major gene for this syndrome has not yet been identified, probably owing to both genetic and phenotypic heterogeneity of this disease. This article describes the clinical evaluation of patients and family members in a large Dutch Gilles de la Tourette Syndrome pedigree and the decisions encountered with respect to phenotyping. The importance of an accurate definition of the Tourette phenotype is discussed, which is highly important for reliable genetic linkage and association studies. Subsequent linkage analysis resulted in three linkage peaks on different chromosomes 3q, 9q, and 13q. Multipoint analysis resulted in a single linkage peak with logarithm of odds score 2.55 with marker D3S1311 on chromosome 3q.

X-linked recessive inheritance of radial ray deficiencies in a family with four affected males.

Radial ray deficiencies are frequently associated with additional clinical anomalies and have a heterogeneous aetiology. X-linked forms are extremely rare. We report a family in which four male relatives show bilateral absence of the radius with presence of the thumbs and associated anomalies. The segregation of the phenotype is suggestive for X-linked recessive inheritance. This is confirmed by performing linkage analysis using 24 markers spanning the X chromosome in which a maximum lod score of 1.93 for DXS8067 and DXS1001 is obtained. We defined a critical region of maximal 16.2 cM on the X chromosome with haplotype analysis.