Alternating Hemiplegia of Childhood

What is Alternating Hemiplegia of Childhood?

This rare disease is a neurological, genetic condition that generally appears when an infant reaches 18 months of age.

It was first identified in 1971. The syndrome is rare, occurring in less than 1 in 1 million live births.

The main symptom of the syndrome includes periodic paralysis.

This syndrome is also known as:
AHC; Alternating Hemiplegia of Childhood.

What gene changes cause Alternating Hemiplegia of Childhood?

⅔ of cases of the syndrome are the result of mutations in the ATP1A3 gene. The remaining cases are caused by mutations in the following genes- CANA1A, SLC1A3, ATP1A2.

The condition may be the result of a de novo mutation or inherited in an autosomal dominant pattern depending on the specific gene responsible for the syndrome in an individual.

In some cases, a genetic syndrome may be the result of a de-novo mutation and the first case in a family. In this case, this is a new gene mutation which occurs during the reproductive process.

In the case of autosomal dominant inheritance just one parent is the carrier of the gene mutation, and they have a 50% chance of passing it onto each of their children. Syndromes inherited in an autosomal dominant inheritance are caused by just one copy of the gene mutation.

What are the main symptoms of Alternating Hemiplegia of Childhood?

Episodes of temporary paralysis, either in one side of the body, or on both at the same side, or on alternating sides is the major symptom of this syndrome, and this paralysis may last anywhere from minutes to days. Dance-like movements from the limbs and facial muscles are also common.

Some families report that specific environmental factors may trigger the episodes of paralysis including extreme temperatures, crows, sleep interruptions, exercise, specific odors, foods, medicines and noises. However more research into these factors is required.

Seizures, abnormal eye movements and muscle stiffness are also common features of the condition.

Possible clinical traits/features:
Mental deterioration, Intellectual disability, Episodic quadriplegia, Episodic hemiplegia, Bilateral tonic-clonic seizure, Headache, Choreoathetosis, Autosomal dominant inheritance, Nystagmus, Dystonia

How does someone get tested for Alternating Hemiplegia of Childhood?

The initial testing for Alternating Hemiplegia of Childhood syndrome can begin with facial analysis screening, through the FDNA Telehealth telegenetics platform, which can identify the key markers of the syndrome and outline the need for further testing. A consultation with a genetic counselor and then a geneticist will follow.

Based on this clinical consultation with a geneticist, the different options for genetic testing will be shared and consent will be sought for further testing.

Medical information Alternating Hemiplegia of Childhood

Alternating hemiplegia is thought by some to be related to migraine, but as others point out the clinical picture can be very different. Onset is between one and 20 years. The first attacks might be dystonic rather than hemiplegic (in some the onset is with focal seizures - often atypical twitches) and several attacks might occur each month, lasting from a few minutes to a few days. During attacks, there might be nystagmus, strabismus, vasomotor disturbances, and screaming as if in pain. After several attacks more permanent neurological sequelae might persist, including focal pyramidal or extrapyramidal signs. See under 'Hemiplegia - benign, nocturnal, alternating' - for something similar. Cardiac involvement (faulty cardiac repolarization) might be common (Jaffer et al., 2015).
Most cases are sporadic, although there might be a family history of migraine, but note the paper by Mikati et al., (1992), in which the condition is segregating with a balanced translocation (3:9). Mental retardation was a feature in some. A mother and four sons (all mentally handicapped) were reported by Xaidara et al., (1998), and the same family by Kanavakis et al., (2003) and half-sisters (same mother) by Kramer et al., (2000).
Bassi et al., (2004) described a Greek family with four affected in two generations. Because of the partial overlap with familial hemiplegic migraine, the authors screened ATP1A2 and found a novel heterozygous mutation. Another ATP1A2 mutation was reported by Swoboda et al., (2004), but mutations were not found in the six patients reported by Kors et al., (2004) nor in 23 patients reported by Vuillaumier-Barrot et al., (2011). Mutations in ATP1A3 could be responsible for 74% of cases (Heinzen et al., 2012).
Sasaki et al., (2014) studied 35 Japanese patients and found de novo heterozygous mutations in ATP1A2 in 33. They found that Glu815Lys mutations had the most severe phenotype.
Three patients with novel heterozygous missense mutations in the ATP1A3 gene were described by Marzin et al., (2018). Clinical characteristics included severe developmental delay, seizures and early onset movement disorder. No hemiplegic attacks were observed.
Fusco et al. (2003) described 29 individuals from two unrelated families with familial hemiplegic migraine type 2, associated with ATP1A2 gene haploinsufficiency. Four patients suffered from migraine aura without motor weakness, five had a history of seizures, and two had mild mental retardation.

* This information is courtesy of the L M D.

If you find a mistake or would like to contribute additional information, please email us at: [email protected]

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