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For many families affected by rare genetic conditions, genomic testing does not immediately deliver an answer. Now, researchers have combined artificial intelligence, human genetics, and fruit fly experiments to connect variants in BRSK1 with a complex neurodevelopmental disorder. The findings provide a potential diagnosis for several previously unexplained cases while offering clues about how reduced activity of the gene may disrupt nervous system development.

The study, “Monoallelic variants in BRSK1 are associated with a neurodevelopmental disorder with or without epilepsy,” was led by researchers at Baylor College of Medicine, the Duncan Neurological Research Institute at Texas Children’s Hospital, and the Texome Project, together with collaborating institutions. It was published in the American Journal of Human Genetics.

According to Hugo Bellen, PhD, who is co-lead author of the study, the work began with a child enrolled in the Texome Project, which provides genetic testing to medically underserved people with rare, undiagnosed conditions in Texas. Standard analysis of the child’s and parent’s genomes had not identified a cause. AI-MARRVEL, an artificial intelligence–based tool that analyzes genomic and clinical information to prioritize candidate disease variants, highlighted a rare change in BRSK1. Through GeneMatcher, the researchers identified nine additional affected individuals with rare heterozygous variants in the gene, bringing the group to 10 people from seven unrelated families. The team then modeled three patient-derived variants in Drosophila melanogaster to test their effects in a living organism.

The “affected individuals present with developmental delay and variable phenotypes including anxiety, attention-deficit hyperactivity disorder (ADHD), autism, and seizures,” the authors wrote, adding that the severity and symptoms varied. Symptoms differed even among relatives carrying the same variant, suggesting variable expressivity.

“We studied the fly equivalent of BRSK1, called sff (sugar-free frosting), and found that this gene is active primarily in neurons, mirroring the expression pattern seen in humans,” added Mingxi Deng, PhD, who is first author and a postdoctoral fellow in the Bellen lab. “When the fly gene was disabled, the flies developed difficulties moving, showed increased sensitivity to stressors that can trigger seizure-like behavior, became more vulnerable to heat-induced paralysis and lived shorter lives. These findings indicated that the gene is essential for normal nervous system function.”

Introducing normal human BRSK1 largely corrected the behavioral and neurological defects, whereas three variants (BRSK1^p.Ile202Val, BRSK1^p.Arg237Cys, and BRSK1^p.Thr406Ile) found in affected individuals produced only a partial rescue. The patient variants also failed to normalize neuromuscular junction structure or levels of Futsch, a protein involved in organizing neuronal microtubules. Together, the experiments suggest that the variants partially reduce BRSK1 activity rather than eliminating it.

“Microtubule disruption has been linked to several neurodevelopmental and neurological disorders,” Deng said. “Our findings suggest that reduced BRSK1 function interferes with the cellular machinery needed for healthy brain development and communication between neurons.”

BRSK1 encodes a kinase involved in neuronal polarization, synaptic function, and the internal organization of nerve cells. Reduced activity may therefore interfere with the cellular machinery neurons need to develop and communicate. “This work improves our understanding of the genetic causes of neurodevelopmental disorders and highlights the power of combining AI-driven gene discovery with experimental studies in model organisms to uncover new rare diseases and their underlying biology,” Bellen said.

The diagnosis may help participating families understand the source of their condition and could guide recognition of additional cases. Future studies will be needed to determine why the same variant can produce markedly different symptoms and to define more precisely how altered BRSK1 activity affects the developing brain.

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