Gain-of-function variants in the ion channel gene TRPM3 underlie a spectrum of neurodevelopmental disorders

Abstract

TRPM3 is a temperature- and neurosteroid-sensitive plasma membrane cation channel expressed in a variety of neuronal and non-neuronal cells. Recently, rare de novo variants in TRPM3 were identified in individuals with developmental and epileptic encephalopathy (DEE), but the link between TRPM3 activity and neuronal disease remains poorly understood. We previously reported that two disease-associated variants in TRPM3 lead to a gain of channel function (Van Hoeymissen et al., 2020; Zhao et al., 2020). Here, we report a further ten patients carrying one of seven additional heterozygous TRPM3 missense variants. These patients present with a broad spectrum of neurodevelopmental symptoms, including global developmental delay, intellectual disability, epilepsy, musculo-skeletal anomalies, and altered pain perception. We describe a cerebellar phenotype with ataxia or severe hypotonia, nystagmus, and cerebellar atrophy in more than half of the patients. All disease-associated variants exhibited a robust gain-of-function phenotype, characterized by increased basal activity leading to cellular calcium overload and by enhanced responses to the neurosteroid ligand pregnenolone sulphate, when co-expressed with wild-type TRPM3 in mammalian cells. The antiseizure medication primidone, a known TRPM3 antagonist, reduced the increased basal activity of all mutant channels. These findings establish gain-of-function of TRPM3 as the cause of a spectrum of autosomal dominant neurodevelopmental disorders with frequent cerebellar involvement in humans, and provide support for the evaluation of TRPM3 antagonists as a potential therapy.

Primidone improves symptoms in TRPM3‐linked developmental and epileptic encephalopathy with spike‐and‐wave activation in sleep

“…Recent reports have identified two de novo TRPM3 variants, p.(V1002M) and p.(S1133P), as gain‐of‐function channels in the heterozygous condition, showing an increased intracellular calcium ([Ca 2+ ] i ) level at basal conditions and elevated [Ca 2+ ] i influx after stimulation by PS 8,12,13 . Additional whole cell patch‐clamp experiments further confirmed the elevated basal activity of S1133P mutant in the heterozygous condition (WT+S1133P; Figure 1).…”

“…[14][15][16][17] Very recently, another report was published showing seven additional de novo variants of TRPM3. 13 Various disease-associated variants including the p.Val-1002Met variant identified in an affected individual in this study (Patient 2) render TRPM3 overactive, resulting in increased Ca 2+ and Na + influx into the cell, both in basal conditions and upon stimulation with PS or heat. 8,12 In addition, also the p.Ser1133Pro variant resulted in an elevated basal activity and an increased Ca 2+ influx after PS stimulation.…”

“…11 TRPM3 is known to act as a temperature sensor in sensory neurons from dorsal root ganglion and trigeminal ganglion neurons, but is also expressed in various other brain areas. 7,12,13 Following the first report of pathogenic TRPM3 variants in eight individuals with moderate-to-severe DEE in 2019, nine further individuals with TRPM3 variants with and without epilepsy phenotypes have been reported. [14][15][16][17] Very recently, another report was published showing seven additional de novo variants of TRPM3.…”

“…8,12 In addition, also the p.Ser1133Pro variant resulted in an elevated basal activity and an increased Ca 2+ influx after PS stimulation. 13 Recently, the antiseizure medication primidone was reported to suppress TRPM3 activity in HEK293 cells overexpressing mouse TRPM3 (HEK mTRPM3 cells) and isolated nociceptive rat dorsal root ganglia neurons in vitro, and also in vivo in a PSinduced chemical pain mouse model. 11 Primidone is metabolized to phenobarbital and phenylethylmalonamide (PEMA), and all three metabolites have their individual effects.…”

“…Following the first report of pathogenic TRPM3 variants in eight individuals with moderate‐to‐severe DEE in 2019, nine further individuals with TRPM3 variants with and without epilepsy phenotypes have been reported 14–17 . Very recently, another report was published showing seven additional de novo variants of TRPM3 13 . Various disease‐associated variants including the p.Val1002Met variant identified in an affected individual in this study (Patient 2) render TRPM3 overactive, resulting in increased Ca 2+ and Na + influx into the cell, both in basal conditions and upon stimulation with PS or heat 8,12 .…”