A Novel De Novo Gain-of-Function CACNA1D Variant in Neurodevelopmental Disease With Congenital Tremor, Seizures, and Hypotonia.

Background and objectives: De novo gain-of-function variants in the CACNA1D gene, encoding the L-type voltage-gated Ca²⁺ channel Ca_V1.3, cause a multifaceted syndrome. Patients show variable degrees of autism spectrum disorder, developmental delay, epilepsy, and other neurologic and endocrine abnormalities (primary aldosteronism and/or hyperinsulinemic hypoglycemia). We study here a novel variant [c.3506G>A, NM_000720.4, p.(G1169D)] in 2 children with the same CACNA1D mutation but different disease severity.

Methods: The clinical data of the study patients were collected. After molecular analysis and cloning by site-directed mutagenesis, patch-clamp recordings of transfected tsA201 cells were conducted in whole-cell configuration. The functional effects of wild-type and mutated channels were analyzed.

Results: One child is a severely affected boy with a novel de novo CACNA1D variant with additional clinical symptoms including prenatal-onset tremor, congenital respiratory insufficiency requiring continuous positive airway pressure ventilation, and sensorineural deafness. Despite episodes of hypoglycemia, insulin levels were normal. Aldosterone:renin ratios as a screening parameter for primary aldosteronism were variable. In the second patient, putative mosaicism of the p.(G1169D) variant was associated with a less severe phenotype. Patch-clamp electrophysiology of the p.(G1169D) variant in a heterologous expression system revealed pronounced activity-enhancing gating changes, including a shift of channel activation and inactivation to more hyperpolarized potentials, as well as impaired channel inactivation and deactivation. Despite retained sensitivity to the Ca²⁺ channel blocker isradipine in vitro, no beneficial effects of isradipine or nifedipine treatment were observed in the index case.

Discussion: Through this report, we expand the knowledge about the disease presentation in patients with CACNA1D variants and show the novel variant's modulatory effects on Ca_V1.3 gating.