Symptom Onset in Classic Rett Syndrome: Analysis of Initial Clinical Severity Scale Entries

To assess clinical features of Rett Syndrome (RTT) at registration into the NIH-sponsored Natural History (NH) study using the Clinical Severity Scale (CSS).

The CSS was established in 2000 to assess characteristics of individuals with RTT and related disorders. We analyzed the CSS at enrollment into the NH study of all individuals with classic RTT.

The CSS of 1258 individuals was utilized to examine three historical items (age at regression, age at onset of hand stereotypies, and head growth) and ten clinical features at initial enrollment.

Among historical items, age at regression was most prominent after age 12 months with 8% regressing prior to this, hand stereotypies were most common after 18 months with 30% occurring before, and head growth was substantially lower overall. Hand use, ambulation, and communication skills were reduced in most.

These findings reflect core clinical criteria for classic RTT and mirror the top concerns registered independently by parents or caregivers. The CSS is an important analytic tool for association of relative differences in clinical outcome with specific MECP2 variant groups and has been important in establishing entrance criteria in RTT clinical trials. The range of age-specific CSS features will continue to inform the RTT NH as well as provide stratification and selection in future clinical trials, especially those involving younger participants.