Cause
Recent research suggests that AHC is caused by a de novo (spontaneous) genetic mutation in the ATP1A3 gene on chromosome 19 (locus 19q13.31) which encodes enzyme ATP1A3. A small number of cases seem to be caused by a mutation in the ATP1A2 gene. Where the mutation is inherited, it has the autosomal dominant pattern of inheritance.Previously AHC was thought to be a form of complicated migraine because of strong family histories of migraine reported in AHC cases. AHC has also been considered to be a movement disorder or a form of epilepsy. Suggested causes have included channelopathy, mitochondrial dysfunction, and cerebrovascular dysfunction. The disorder most closely related to AHC is familial hemiplegic migraine which is caused by a mutation in a gene for calcium channel receptors. It was thus thought that AHC may be caused by a similar channelopathy. Diagnosis
As of 1993 only approximately 30 people with AHC had been described in scientific literature. Due to the rarity and complexity of AHC, it is not unusual for the initial diagnosis to be incorrect, or for diagnosis to be delayed for several months after the initial symptoms become apparent. The average age of diagnosis is just over 36 months. Diagnosis of AHC is not only difficult because of its rarity, but because there is no diagnostic test, making this a diagnosis of exclusion. There are several generally accepted criteria which define this disorder, however other conditions with a similar presentation, such as HSV encephalitis, must first be ruled out.
Some studies have found it to be very effective in reducing the duration, severity, and frequency of hemiplegic attacks. It is generally considered the best treatment available, but this drug is thought by some to be of little benefit to AHC patients. Many patients suffer adverse effects without seeing any improvement. Flunarizine also causes problems because it is difficult for patients to obtain, as it is not readily available in the United States. Sodium oxybate
In 2009 through 2011 clinical research at the University of Utah investigated whether sodium oxybate, also known as Gamma-Hydroxybutyric acid is an effective treatment for AHC. Thus far, only a small number of patients have been sampled, and no conclusive results are yet available. While some success has been had thus far with the drug, AHC patients have been known to respond well initially to other drugs, but then the effectiveness will decline over time. Currently, sodium oxybate is used as a narcolepsy-cataplexy treatment, though in the past it has been used controversially in nutritional supplements. This drug was chosen to test because of a possible link between the causes of narcolepsy-cataplexy and AHC. References
External links
Alternating Hemiplegia Information Page at NINDS
Homepage of the Alternating Hemiplegia of Childhood Foundation (AHCF).