Homozygous SLC6A17 Mutations Cause Autosomal-Recessive Intellectual Disability with Progressive Tremor, Speech Impairment, and Behavioral Problems
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SourceAmerican Journal of Human Genetics, 96, 3, (2015), pp. 386-396
Article / Letter to editor
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Primary and Community Care
American Journal of Human Genetics
SubjectRadboudumc 0: Other Research DCMN: Donders Center for Medical Neuroscience; Radboudumc 18: Healthcare improvement science RIHS: Radboud Institute for Health Sciences; Radboudumc 19: Nanomedicine RIMLS: Radboud Institute for Molecular Life Sciences; Radboudumc 7: Neurodevelopmental disorders DCMN: Donders Center for Medical Neuroscience; Radboudumc 9: Rare cancers RIHS: Radboud Institute for Health Sciences
We report on Dutch and Iranian families with affected individuals who present with moderate to severe intellectual disability and additional phenotypes including progressive tremor, speech impairment, and behavioral problems in certain individuals. A combination of exome sequencing and homozygosity mapping revealed homozygous mutations c.484G>A (p.Gly162Arg) and c.1898C>G (p.Pro633Arg) in SLC6A17. SLC6A17 is predominantly expressed in the brain, encodes a synaptic vesicular transporter of neutral amino acids and glutamate, and plays an important role in the regulation of glutamatergic synapses. Prediction programs and 3D modeling suggest that the identified mutations are deleterious to protein function. To directly test the functional consequences, we investigated the neuronal subcellular localization of overexpressed wild-type and mutant variants in mouse primary hippocampal neuronal cells. Wild-type protein was present in soma, axons, dendrites, and dendritic spines. p.Pro633Arg altered SLC6A17 was found in soma and proximal dendrites but did not reach spines. p.Gly162Arg altered SLC6A17 showed a normal subcellular distribution but was associated with an abnormal neuronal morphology mainly characterized by the loss of dendritic spines. In summary, our genetic findings implicate homozygous SLC6A17 mutations in autosomal-recessive intellectual disability, and their pathogenic role is strengthened by genetic evidence and in silico and in vitro functional analyses.
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