A novel p.Arg970X mutation in the last exon of the CDKL5 gene resulting in late-onset seizure disorder.

Classic Rett Syndrome (RS) is a neurodevelopmental disorder due to mutations in the MECP2 gene in Xq28. Atypical RS with severe early-onset encephalopathy and therapy-resistant epilepsy can be due to mutations in the CDKL5 (Cyclin-Dependent Kinase-like 5) gene in Xp22. We here report a 14-year-old female with a RS-like clinical picture, and well-controlled seizures. MECP2 gene testing was negative, but subsequent sequencing of the CDKL5 gene revealed the c. 2908 C>T nonsense mutation (p.Arg970X) in the last exon, not previously described in other patients or controls. The less severe phenotype might be due to the position of the mutation in the last exon of the CDKL5 gene.