SNP Shot: Genomic Insights

Alternating hemiplegia of childhood (AHC) is a rare neurological disorder characterized by repeated episodes of temporary paralysis that typically affects one side of the body (hemiplegia). The paralysis may switch sides during an episode or affect both sides simultaneously. These episodes usually begin before 18 months of age and can last from a few minutes to several days.

Besides paralysis, individuals with AHC may experience sudden attacks of involuntary muscle movements. These attacks can manifest as uncontrolled limb movements (choreoathetosis), sustained muscle contractions (dystonia), involuntary eye movements (nystagmus), or difficulty breathing (dyspnea). Affected individuals may also exhibit sudden skin flushing or paleness, which can occur during or independently of hemiplegic episodes.

Triggers like stress, fatigue, cold temperatures, or bathing can sometimes provoke episodes of hemiplegia or uncontrolled movements, although the trigger is often unknown. A hallmark of AHC is the temporary disappearance of all symptoms during sleep, only to return shortly after waking. The frequency and duration of episodes tend to increase during childhood before gradually decreasing. While uncontrolled muscle movements may eventually disappear, the hemiplegic episodes generally persist throughout life.

AHC often leads to cognitive impairments ranging from mild to severe. Developmental delays and intellectual disability are common in affected individuals, and their cognitive abilities tend to decline progressively.

Inheritance:

AHC is typically inherited in an autosomal dominant pattern, meaning that only one copy of a mutated gene is needed to cause the disorder. Most cases arise from new, spontaneous mutations in a gene, with no prior family history of AHC. However, familial inheritance is possible. Interestingly, the symptoms tend to be less severe when AHC is present in multiple family members compared to when only one individual is affected.