September 2026 Research Update

This month added a reminder that alternating hemiplegia of childhood (AHC) can appear suddenly and look like an inflammatory brain problem, even when common tests do not show inflammation. In three children with ATP1A3 gene variants, the initial picture resembled autoimmune encephalitis or related syndromes, but later evaluation identified ATP1A3-related diagnoses including AHC. The shared pattern was acute, severe neurologic symptoms with normal MRI and normal spinal fluid, where genetics helped clarify what was going on. [1]

Across the three children, genetic testing found ATP1A3 variants (including Arg756 in two cases), and the final diagnoses spanned several ATP1A3-related conditions: rapid-onset dystonia-parkinsonism (RDP), relapsing encephalopathy with cerebellar ataxia (RECA), and AHC. The report described major symptoms during the episodes, such as weakness or paralysis, speech and swallowing problems, abnormal movements, and seizures. The main message was not that MRI or spinal fluid tests are unhelpful, but that they can be normal in ATP1A3-related attacks, which may delay recognition if genetics is not considered. [1]

For families, this mainly adds understanding about diagnosis rather than pointing to a new treatment. It suggests that when a child has a sudden, severe episode that resembles autoimmune brain inflammation, ATP1A3-related conditions (including AHC) can be part of the explanation even if MRI and spinal fluid results look normal. Because this evidence comes from only three patients, it cannot show how often this happens, but it helps clarify one way AHC can be missed early and why genetic testing may be discussed in similar situations. [1]

This month brought progress on a practical need in AHC: measuring symptoms in a consistent way across centers. A European group developed and tested the Alternating Hemiplegia of Childhood Rating Scale (AHC-RS) and found that different raters scored patients very similarly, which is important for tracking change over time. The scale also lined up in expected ways with existing movement and disability ratings, supporting that it is capturing meaningful aspects of function. This helps make research and care discussions clearer by giving a shared way to describe how someone is doing. [2]

In 48 patients from Spain, France, and Italy, the AHC-RS showed excellent inter-rater reliability across domains (ICC 0.95 to 0.99). The total AHC-RS score had moderate correlations with Burke-Fahn-Marsden movement and disability scores (rho 0.58 and 0.63), and some parts of the scale related to each other more strongly than others (for example, the non-paroxysmal score correlated with adaptive function, r 0.74). The authors noted gaps still to fill, such as not testing whether scores stay stable when the same person is rated again later, and that some items rely on recalling events over the prior 6 months. [2]

For patients and caregivers, this is most likely to matter gradually, because better measurement tools usually affect research and clinic tracking before they affect daily management. The AHC-RS may make it easier for different teams to describe both ongoing challenges and episode-related problems in the same language, which can support clearer follow-up and more comparable clinical trials. What remains uncertain is how well this scale captures change within one person over time and how it performs in all age groups, since some testing (like repeat ratings over time) was not done in this report. [2]