The symptoms as well as the severity of the disease varied widely among the patients depending on the gene alteration.
Individuals carrying the p.Arg320His variant showed the MEAK-Syndrome (Myoclonus and Ataxia due to Potassium channel mutation). Clinical features include:
• Age at onset: 3 – 15 years of age (mean ~10 years)
• Progressive myoclonus (involuntary twitching of muscles)
• Seizures (generalized, tonic-clonic, myoclonic)
• Ataxia (gait difficulties, clumsiness, difficulty with balance and in movement)
• cognitive decline (some patients)
• wheelchair dependency by adulthood (some patients)
• developmental delay (very rare)
Individuals carrying the p.Ala421Val variant showed Developmental Epileptic Encephalopathy with Ataxia. Clinical features include:
• Global developmental delay
• Seizures (absence, generalized, tonic-clonic, myoclonic)
• Ataxia (gait difficulties, clumsiness, difficulty with balance and in movement)
• Muscular hypotonia (some patients)
Some individuals showed Intellectual disability without seizures.
• Known gene variants with this phenotype: p.Arg339Ter, p.Thr399Met, p.Gln492Ter, p.Arg317His
• Global developmental delay
• Mild to moderate intellectual disability
Some other patients also showed:
• Mild non-progressive myoclonus or “tremor” (1 patient, p.Cys208Tyr)
• Early-onset epilepsy with focal migrating seizures and developmental delay (1 patient, p.Ala513Val)
• Developmental delay with epilepsy and MRI abnormalities (1 patient, p.Arg317Ser)
KCNC1