Clinical Characteristics

The core phenotype includes early-onset epileptic encephalopathy, especially epileptic spasms, intractable seizures, marked developmental delay and severe to profound intellectual disability. Truncal hypotonia is usual, and some patients also show pyramidal and/or extrapyramidal hypertonia of the limbs. Microcephaly may be present but is not constant. The clinical spectrum is relatively narrow, but severity can vary, and some patients may be diagnosed with a nonspecific early infantile epileptic encephalopathy rather than a recognizable syndrome.