Main clinical features

Mutations (changes) in the STXBP1 gene are an important cause of what is called early infantile epileptic encephalopathy (EIEE). This is a severe brain disorder presenting at early age with seizures, developmental delay and possibly also behavioural and other neurological symptoms. For example, some patients show autistic features or movement disorders. Other signs and symptoms caused by STXBP1 mutations could be feeding difficulties and severe speech impairment. The disorder caused by STXBP1 mutations is often referred to as STXBP1-encephalopathy (STXBP1-E).

A more extensive description of the clinical spectrum of STXBP1 mutations can be found in the section Parents – Clinical characteristics and at, which also contains an extensive section for laymen (patient families and other caregivers)


STXBP1 mutations are rare. Due to a very limited number of cases (about 200) identified so far, it is difficult to predict the prevalence of the disorder. A scientific publication by Stamberger and colleagues (2016) estimated a frequency of STXBP1 mutations of approximately 1 per 90.000 births in a Danish cohort. A more recent study by Uddin and colleagues (2017) calculated that STXBP1 mutations are found in 3% of clinically identified epilepsy cases. More studies are needed for a more accurate estimation of the frequency of STXBP1 mutations.


STXBP1 mutations are inherited in an autosomal dominant manner. This means that anyone carrying the mutation has a 50% chance of transmitting the mutation to future offspring. However, individuals with STXBP1 mutations are not known to reproduce.  To date, nearly all reported cases have resulted from de novo mutations. That means that the individuals carrying the mutation represent a single occurrence in a family and the mutation was not detected in either one of their parents. Therefore, parents of a child with a STXBP1 mutation usually have a very low risk of a second child with the same condition. The recurrence risk (probably <1%) is however greater than that of the general population since germline mosaicism in one of the parents cannot be excluded. This means that the mutation that is absent in blood cells of the parents, might still be present in their sperm or egg cells and therefore again be transmitted to future children. It is important to accentuate that this only occurs in rare instances. If desired, options of prenatal diagnosis can be discussed with a genetic counselor