Interestingly these missense mutations that result in a mislocalisation of the CDKL5 protein are associated with severe developmental delay which was apparent within the first months of life characterised by early and generalised hypotonia, and autistic features, and as well as early infantile spasms.
Importantly, one member of the family, CDKL5, has been implicated in atypical Rett syndrome, West syndrome, and X-linked infantile spasm, all including MR as a manifestation.
In conclusion, our report show that search for mutations in CDKL5 is indicated in girls with early onset of a severe intractable seizure disorder or infantile spasms with severe hypotonia, and in girls with RTT-like phenotype and early onset seizures, though, in our cohort, mutations in CDKL5 account for about 10% of the girls affected by these disorders.
This combination of early infantile spasms followed by a complex movement disorder contributes further to extent the pleiotropy of the ARX-linked "interneuronopathy" and should lead the clinician to ARX mutation screening.
In conclusion, our report show that search for mutations in CDKL5 is indicated in girls with early onset of a severe intractable seizure disorder or infantile spasms with severe hypotonia, and in girls with RTT-like phenotype and early onset seizures, though, in our cohort, mutations in CDKL5 account for about 10% of the girls affected by these disorders.
ARX is a crucial gene for the development of interneurons in the fetal brain, and a polyalanine expansion mutation of ARX causes mental retardation and seizures, including those of West syndrome, in males.
A screen for CDKL5 mutations is useful in patients, mainly females, with a history of early onset intractable seizures and becomes mandatory when idiopathic infantile spasms and/or atypical Rett syndrome features are also present.
Mutations in the human ARX gene have been shown to cause nonsyndromic X-linked mental retardation (MRX) as well as syndromic forms such as X-linked lissencephaly with abnormal genitalia (XLAG), Partington syndrome and X-linked infantile spasm.
Lissencephaly caused by LIS1 or DCX mutation frequently results in West syndrome, while lissencephaly due to ARX mutation is associated with the most severe form of epilepsy but never results in West syndrome nor infantile spasms.
CDKL5 mutations are a significant cause of infantile spasms and early epileptic seizures in female patients, and of a later intractable seizure disorder, irrespective of whether they have suspected Rett syndrome.
Epilepsy with mutation of the CDKL5 gene causes early seizures and is a variant of Rett syndrome (MIM (312750), which is reported typically as infantile spasms.
Although the phenotype of CDKL5 mutation is similar to Rett syndrome caused by MECP2 mutation, the former is characterized by early-onset seizures and association with West syndrome.
CDKL5 mutations are a significant cause of infantile spasms and early epileptic seizures in female patients, and of a later intractable seizure disorder, irrespective of whether they have suspected Rett syndrome.
Mutations in the CDKL5 gene (also known as STK9) have recently been shown to cause early onset epilepsy and severe mental retardation (ISSX or West syndrome).