Genetic Insights Into Hypothalamic Hamartoma: Unraveling Somatic Variants
Lina Sami1, Mathilde Chipaux1, Sarah Ferrand-Sorbets1
1From the Institut du Cerveau-Paris Brain Institute-ICM (L.S., M.D., J.-M.D.S.A., E.L., Sara Baldassari, Stephanie Baulac), Sorbonne Université, Inserm, CNRS, Hôpital de la Pitié Salpêtrière; Department of Pediatric Neurosurgery (M.C., S.F.-S., C.B., E.R., S.R., G.D., R.C.), Rothschild Foundation Hospital EPICARE; Department of Medical Genetics (J.-M.D.S.A., E.L.), AP-HP, Sorbonne Université, Hôpital de la Pitié Salpêtrière; and Université de Paris Cité (H.A.-B.), service d'Anatomie Pathologique, AP-HP, Hôpital Lariboisière, DMU DREAM, Biobank BB-0033-00064, UMR 1141, INSERM, Paris, France.
Objectives:
Hypothalamic hamartomas (HHs) are rare developmental brain lesions associated with drug-resistant epilepsy and often subjected to epilepsy surgery. Brain somatic variants in genes affecting the Sonic hedgehog (Shh) and primary cilia signaling pathways have been implicated in approximately 50% of nonsyndromic HH cases. This study aims to characterize a new cohort of 9 HH cases and elucidate their genetic etiology.
Methods:
We recruited 9 HH cases including 8 nonsyndromic cases of which 4 were type IV HH. Genomic DNA was extracted from peripheral blood and surgical brain tissues, and somatic variants were investigated using high-depth whole-exome sequencing.
Results:
Pathogenic somatic variants in known HH genes (GLI3, OFD1, and PRKACA) were identified in 7 of the 9 cases. In addition, a 2-hit mutational event comprising a germline variant (predicted to impair kinase activity) and a somatic loss-of-heterozygosity was identified in TNK2, a gene encoding a brain-expressed tyrosine kinase.
Discussion:
Our findings reinforce the role of somatic variants in Shh and cilia genes in HH cases while also shedding light on TNK2 as a potential novel disease-causing gene. This study emphasizes the increasing importance of brain mosaicism in epilepsy disorders and underscores the critical role of genetic diagnosis derived from resected brain tissue.
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