Alternating Hemiplegia of Childhood (AHC) is a rare neurological disorder that primarily affects children. It is characterized by recurrent episodes of temporary paralysis or weakness, often impacting one side of the body, though it can shift to the other side or even affect both sides simultaneously. This condition, first described in 1971, has a profound impact on a child’s development, presenting a complex and often unpredictable course.
Defining Alternating Hemiplegia of Childhood
AHC is an exceptionally rare, chronic neurodevelopmental disorder that typically becomes apparent in infancy or early childhood, usually before 18 months of age. The term “alternating hemiplegia” directly refers to its defining symptom: episodes of weakness or paralysis that can alternate between the left and right sides of the body. These episodes can also sometimes manifest as full-body paralysis (quadriplegia).
The episodic nature of AHC means that these periods of weakness or paralysis are transient, lasting from minutes to days, or even weeks in some instances. A distinctive feature is that these symptoms often resolve completely during sleep, only to reappear shortly after waking. Beyond the hallmark paralysis, AHC involves a wide spectrum of neurological issues that can vary significantly among individuals and even within the same child over time.
Key Features and Symptoms
The most prominent symptom of AHC is the paroxysmal, or sudden and episodic, attacks of hemiplegia. These attacks involve weakness or paralysis that can affect one side of the body, shift to the other, or involve all four limbs. The duration and frequency of these episodes are highly variable, occurring daily, weekly, or less often.
Beyond the hemiplegic attacks, children with AHC experience a range of other associated symptoms. Dystonia, characterized by sustained muscle contractions causing twisting or repetitive movements and abnormal postures, is a common feature. Involuntary eye movements, specifically nystagmus, are frequently observed and can be among the earliest signs of the disorder.
Other symptoms include autonomic disturbances, which can manifest as changes in skin color, sweating, or fluctuations in body temperature. Developmental delays are almost universally present, affecting motor skills, cognitive function, and speech. While less common than the non-epileptic paroxysmal events, some children with AHC may also experience epileptic seizures. Additionally, ataxia, a lack of muscle coordination leading to balance and walking problems, is another symptom that can occur.
The Underlying Causes
The primary cause of Alternating Hemiplegia of Childhood is typically traced to mutations in the ATP1A3 gene. This gene provides the instructions necessary for producing a protein that is a subunit of the sodium-potassium pump (Na+/K+-ATPase). This pump plays a fundamental role in maintaining the balance of sodium and potassium ions across the membranes of nerve cells in the brain.
When a mutation occurs in the ATP1A3 gene, it disrupts the proper functioning of this ion pump, leading to an imbalance of ions within the nerve cells. This cellular dysfunction is believed to underlie the diverse neurological symptoms observed in AHC. While ATP1A3 mutations account for approximately 70-80% of AHC cases, other genes such as ATP1A2 and RHOBTB2 have also been implicated in a smaller percentage of individuals. In most instances, the ATP1A3 gene mutation is de novo, meaning it is a new mutation that was not inherited from either parent. However, in rare cases, the mutation can be inherited.
Diagnosis and Management Approaches
Diagnosing AHC relies on clinical evaluation, identifying the characteristic pattern of symptoms. Genetic testing for ATP1A3 mutations is crucial for confirmation. Other conditions that might present with similar symptoms must also be ruled out.
There is no cure for AHC; management focuses on alleviating symptoms and providing supportive care. A multidisciplinary approach involves a team of specialists including neurologists, physical therapists, occupational therapists, speech therapists, and educators. Medications like flunarizine, a calcium antagonist, are often used to reduce the frequency, severity, and duration of attacks. Benzodiazepines may be prescribed to induce sleep, which can resolve an acute episode.
Therapies, including physical, occupational, and speech therapy, address developmental delays and improve motor skills, coordination, and communication. Educational support accommodates learning differences. Identifying and managing triggers (e.g., stress, fatigue, temperature changes, illness) helps prevent or lessen episode severity. Individualized care plans are essential, as symptoms and needs vary considerably.