Upregulation versus loss of function of NTRK2 in 44 affected individuals leads to 2 distinct neurodevelopmental disorders

Abstract

Purpose: Heterozygous pathogenic variants in NTRK2 (HGNC: 8032) have been associated with global developmental delay. However, only scattered cases have been described in small or general studies. The aim of our work was to consolidate our understanding of NTRK2-related disorders and to delineate the clinical presentation.

Methods: We reported an extended cohort of 44 affected individuals, of whom 19 are from the literature and 25 were previously unreported.

Results: Our analysis led to splitting the cohort into 2 entities.

Conclusion: One group had variants in the cholesterol-binding motif of the transmembrane domain, with most of these being the recurrent variant c.1301A>G p.(Tyr434Cys). These variants probably lead to upregulation of tropomyosin receptor kinase B activity and to a severe phenotype of developmental delay/intellectual disability, muscular hypotonia, therapy-refractory epilepsy, visual impairment and blindness, and feeding difficulties. The second group had truncating variants or variants that presumably disturb the 3D structure of the protein leading to loss of function. These individuals had a remarkably milder phenotype of developmental delay, obesity, and hyperphagia.

Keywords: Blindness; Obesity; TRKB; Transmembrane domain; Tyrosine kinase domain.