ATP1A3: Sisyphus with a purpose

ATP1A3. The ATPases are the “Sisphyean” workhorses of cells, perpetually bound to utilize energy generated by mitochondria to pump ions across cell membranes. This is essential to the maintenance of the intra/extracellular electrochemical gradient. ATP1A3 codes for the α3 subunit of the Na+-K+ ATPase, which utilizes ATP to actively transport sodium out of the cell and potassium into the cell. In the brain, this gradient is critical for cell signaling and for maintaining electrochemical stability, enabling cell excitation and action potential propagation. Both ATP1A3 and one of its counterparts, ATP1A2, are expressed in neurons during embryonal brain development, and ATP1A3 is also thought to contribute to regulation of non-ionic neuronal transporters and receptors. However, whereas ATP1A2 is primarily expressed in glial cells postnatally and into adulthood, ATP1A3 continues to be expressed primarily in neurons, with particular enrichment in excitatory neurons. Here is a brief overview of the clinical spectrum of ATP1A3-related disorders.

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CLDN5, the blood brain barrier, and alternating hemiplegia of childhood

AHC. Amongst the various episodic neurological disorders of childhood, alternating hemiplegia of childhood (AHC) is one of the most mysterious conditions. AHC is characterized by transient hemiplegic attacks and a wide range of other neurological features including dystonic attacks, seizures, neurodevelopmental features, and autonomic symptoms. Recurrent de novo variants in ATP1A3 represent the most common cause of AHC, even though a small subset of individuals have disease-causing variants in other genes. In a recent paper, de novo variants in CLDN5 were identified. In contrast to known causes of AHC, CLDN5 implicates an entirely new disease mechanism – disruptions of the blood-brain barrier. Continue reading

ATP1A3 links alternating hemiplegia of childhood with genetic dystonia and parkinsonism

Alternating Hemiplegia of Childhood (AHC). Acute hemiplegia in children, i.e. weakness of one side of the body, is always a medical emergency. Causes for a sudden hemiplegia can include intracranial bleeds, tumors and rare metabolic disorders. Immediate diagnostic work-up is paramount. In some children, no cause can be found on brain imaging and extensive testing, and the episode remits after hours or days. Strangely, during a following episode, the other side of the body is affected. This condition has been named Alternating Hemiplegia of Childhood (AHC) by Verret and Steele in 1971. AHC is an enigmatic disorder, which is sometimes associated with epilepsy, developmental delay and dystonia. Even though some cases with mutations in SCN1A, CACNA1A, and ATP1A2 have reported, most cases of AHC are unresolved. Given some resemblance with epilepsy and familial hemiplegic migraine, many children with AHC are followed up by epileptologists. The major cause of AHC has now been identified in a recent study… Continue reading