Updating the profile of C-terminal MECP2 deletions in Rett syndrome

Change in gross motor abilities of girls and women with rett syndrome over a 3- to 4-year period

Rett syndrome is a rare but severe neurological disorder typically associated with a mutation in the MECP2 gene. We describe change in gross motor function over 3 to 4 years for 70 subjects participating in the Australian Rett Syndrome Database. Linear regression was used to assess relationships with age, genotype, and general and complex gross motor skills scores measured on the Gross Motor Scale for Rett syndrome. Skills were slightly better or maintained in approximately 40% of subjects and slightly decreased in approximately 60%. Teenagers and women who walked in 2004 were less likely to lose complex skills than those younger. Girls with a p.R294X mutation were more likely to lose complex motor skills, otherwise skill changes were spread across the mutation categories. In conclusion, small changes were observed over this period with greater stability of skills in teenagers and women with the ability to walk.

Two new Rett syndrome families and review of the literature: expanding the knowledge of MECP2 frameshift mutations

BACKGROUND

Rett syndrome (RTT) is an X-linked dominant neurodevelopmental disorder, which is usually caused by de novo mutations in the MECP2 gene. More than 70% of the disease causing MECP2 mutations are eight recurrent C to T transitions, which almost exclusively arise on the paternally derived X chromosome. About 10% of the RTT cases have a C-terminal frameshift deletion in MECP2. Only few RTT families with a segregating MECP2 mutation, which affects female carriers with a phenotype of mental retardation or RTT, have been reported in the literature. In this study we describe two new RTT families with three and four individuals, respectively, and review the literature comparing the type of mutations and phenotypes observed in RTT families with those observed in sporadic cases. Based on these observations we also investigated origin of mutation segregation to further improve genetic counselling.

METHODS

MECP2 mutations were identified by direct sequencing. XCI studies were performed using the X-linked androgen receptor (AR) locus. The parental origin of de novo MECP2 frameshift mutations was investigated using intronic SNPs.

RESULTS

In both families a C-terminal frameshift mutation segregates. Clinical features of the mutation carriers vary from classical RTT to mild mental retardation. XCI profiles of the female carriers correlate to their respective geno-/phenotypes. The majority of the de novo frameshift mutations occur on the paternally derived X chromosome (7/9 cases), without a paternal age effect.

CONCLUSIONS

The present study suggests a correlation between the intrafamilial phenotypic differences observed in RTT families and their respective XCI pattern in blood, in contrast to sporadic RTT cases where a similar correlation has not been demonstrated. Furthermore, we found de novo MECP2 frameshift mutations frequently to be of paternal origin, although not with the same high paternal occurrence as in sporadic cases with C to T transitions. This suggests further investigations of more families. This study emphasizes the need for thorough genetic counselling of families with a newly diagnosed RTT patient.

Altered attainment of developmental milestones influences the age of diagnosis of rett syndrome

The early developmental history prior to the manifestation of Rett syndrome features is of clinical interest. This study describes the attainment of gross developmental milestones and regression, and assesses the relationships between genotype and age at diagnosis. The Australian Rett Syndrome Database and International Rett Syndrome Phenotype Database were used to source a total of 293 confirmed female subjects. Most girls learned to sit, were able to babble or use words, and approximately half learned to walk. Altered milestone attainment was associated with earlier diagnosis. There was variation in the acquisition of milestones, the age of regression, and the age of diagnosis by genotype. Most parents expressed concerns about unusual behaviors or development during infancy, and a more subtle atypical development during infancy was reported for most girls. It is important for clinicians to be aware of variable early development in Rett syndrome and that timely genetic testing is not precluded on this account.

The relationship between MECP2 mutation type and health status and service use trajectories over time in a Rett syndrome population

This study aimed to investigate the trajectories over time of health status and health service use in Rett syndrome by mutation type. Data were obtained from questionnaires administered over six years to 256 participants from the Australian Rett Syndrome Database. Health status (episodes of illness and medication load) and health service use (general practitioner and specialist visits and hospital stays) were summarized into composite scores with Principal Component Analysis. Linear and mixed regression models examined effects of mutation type and other variables on these scores over time. For some mutations (such as p.R255X, p.R168X) health status was poorer at a younger age and improved over time, while for p.R133C it was better at a younger age and deteriorated with time. For those with p.R133C health service use was lowest at a younger age and highest at 25 years. With other mutations, such as p.R255X, p.R270X, p.R294X, C terminal and p.R306C, health service use was higher at a younger age, but dropped off considerably by 25 years of age. Health service use generally declined in parallel with deterioration in health status, although this pattern differed by mutation type, demonstrating important variability in the course of Rett syndrome.