Main clinical features
CNKSR2 syndrome, sometimes referred to a Houge type X-linked intellectual disability, is a newly recognised condition which causes epilepsy together with developmental delay or learning problems, especially affecting speech and language.
The main signs and symptoms of this condition are delay in development, usually noticeable from birth, then onset of seizures around two to three years. When the seizures start, language skills which have been acquired are often lost and may not be regained afterwards to the same extent. Seizures persist through childhood and there is usually a characteristic pattern on the EEG ( brainwave) test, observed when the child is asleep. In later childhood and adulthood seizures may stabilise, though we need to have information from more children and adults to be sure of this. In some cases some sudden jerky movements have been seen ( myoclonic jerks), even in younger children before obvious seizures begin. Learning difficulties are usually present, of a severity which means that children will need some extra help with their education.
Prevalence
Though very few individuals with this disorder have been recognised so far, studies have shown that it most likely accounts for around 1% of individuals who have epilepsy with speech problems, and as testing of the CNKSR2 gene becomes more widely available, more individuals will be described.
At the present time in 2017 fewer than 20 affected individuals have been reported in the literature.
Inheritance
This condition follows what we call an X-linked pattern of inheritance as the CNKSR2 gene lies on the X chromosome.
This means that boys are affected more severely by the condition, as they have only a single X chromosome, whereas girls, if they are affected, may have milder signs as they have a second, normal X chromosome to cancel out the effect of the faulty X.
Sometimes the mother of an affected child will carry the same gene change. It’s important that each family visits their clinical geneticist to discuss the test results for their family, as there may be implications for future pregnancies or for other family members. The geneticist would also be able to discuss the possibility of tests for future pregnancies if wished.