A Rare Missense Variant in TNPO2 in an Individual With a Neurodevelopmental Disability

We report an 87-year-old female with a history of intellectual disability, severe speech impairment and behavioral issues. She was globally delayed in childhood. In adolescence, she had hallucinations, behavioral issues and was institutionalized. Her behavioral issues were treated, and her medical and behavioral course was stable until her 80's when she began to decline cognitively. She died at age 87. Exome sequencing revealed a novel predicted damaging missense variant (c.1913T>G; p.Met638Arg; NM_001136196.2) in the gene encoding Transportin-2 (TNPO2). Heterozygous variants in TNPO2 have been recently associated with an intellectual developmental disorder with hypotonia, impaired speech, and dysmorphic facies (IDDHISD; MIM:619556). Postmortem pathological examination of her brain revealed focal neuronal depletion in the dentate gyrus, CA1, and hilar regions of the hippocampus. These findings are consistent with human gene expression data showing normal to increased expression of TNPO2 in the dentate gyrus and CA1 region of the hippocampus. We suggest that the p.(Met638Arg) variant in TNPO2 is potentially disease-causing and associated with IDDHISD.