Rett syndrome (RTT) is a severe neurodevelopmental disorder of girls, caused by mutations in the X-linked MECP2 gene. Worldwide recognition of the RTT clinical phenotype in the early 1980's allowed many cases to be diagnosed, and established RTT as one of the most common mental retardation syndromes in females. The years since then led to a refinement of the phenotype and the recent elaboration of Revised Diagnostic Criteria (RDC). Here, we study the impact of the presence versus the absence of the use of diagnostic criteria from the RDC to make a diagnosis of RTT on MECP2 mutation detection in Canadian patients diagnosed and suspected of having RTT.

Using dHPLC followed by sequencing in all exons of the MECP2 gene, we compared mutation detection in a historic cohort of 35 patients diagnosed with RTT without the use of specific diagnostic criteria to a separate more recent group of 101 patients included on the basis of strict fulfillment of the RDC.

The MECP2 mutation detection rate was much higher in subjects diagnosed using a strict adherence to the RDC (20% vs. 72%).

These results suggest that clinical diagnostic procedures significantly influence the rate of mutation detection in RTT, and more generally emphasize the importance of diagnostic tools in the assessment of neurobehavioral syndromes.

We describe nine females with Rett Syndrome (RS), aged 14 to 26 years. All had had developmental delay before the end of their first year and had subsequently regressed to profound dementia with apraxia, ataxia, irregular respirations and often also seizures.

The Revised Gesell developmental assessment and Alpern-Boll Developmental Profile were used in modified form. Volumetric measurements of basal ganglia using MRI were compared with the findings in nine age-matched volunteer females. Positron emission scans with [18F]-6-fluorodopa and [11C]-raclopride were performed under light anesthesia with intravenous Propofol, and the findings were compared with those in healthy control girls. Bidirectional sequencing of the coding regions of the MECP2 gene was investigated in blood samples for mutational analyses.

The RS females functioned at a mental age level ranging from about 4 to 15 months. The scores correlated with height, weight and head circumference. Magnetic resonance scans of basal ganglia showed a significant reduction in the size of the caudate heads and thalami in the Rett cases. Positron emission scans demonstrated that the mean uptake of fluorodopa in RS was reduced by 13.1% in caudate and by 12.5% in putamen as compared to the controls, while dopamine D2 receptor binding was increased significantly by 9.7% in caudate and 9.6% in putamen. Mutations in the coding regions of the MECP2 gene were present in all nine patients. No significant correlation between type and location of mutation and volumetric changes or isotope uptake was demonstrable.

Our findings suggest a mild presynaptic deficit of nigrostriatal activity in Rett syndrome.