Mutations of the UPF3B gene, which encodes a protein widely expressed in neurons, are associated with nonspecific mental retardation with or without autism

• Published in: Molecular psychiatry Vol. 15; no. 7; pp. 767 - 776
• Main Authors: Laumonnier, F, Shoubridge, C, Antar, C, Nguyen, L S, Van Esch, H, Kleefstra, T, Briault, S, Fryns, J P, Hamel, B, Chelly, J, Ropers, H H, Ronce, N, Blesson, S, Moraine, C, Gécz, J, Raynaud, M
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-07-2010; Nature Publishing Group
• Subjects: Adult; Amino Acid Substitution - genetics; Animals; Autism; Autistic Disorder - complications; Autistic Disorder - genetics; Behavioral Sciences; Biological Psychology; Cell Line; Codon, Nonsense - genetics; Dendritic spines; Dendritic Spines - metabolism; Down-Regulation; Female; Gene mutations; Genetic aspects; Health aspects; Hippocampus; Hippocampus - metabolism; Humans; Intellectual disabilities; Intellectual Disability - complications; Intellectual Disability - genetics; Life Sciences; Localization; Lymphoblastoid cell lines; Male; Medicine; Medicine & Public Health; Mental retardation; Messenger RNA; Mice; Middle Aged; mRNA turnover; Mutation; Neural coding; Neurobiology; Neurons; Neurons - metabolism; Neurons and Cognition; Neurosciences; Neurotransmission; Nonsense mutation; Nonsense-mediated mRNA decay; original-article; Pedigree; Pharmacotherapy; Physiological aspects; Proteins; Psychiatry; Risk factors; RNA Stability; RNA-Binding Proteins - genetics; RNA-Binding Proteins - metabolism; France; Australia; mental retardation; nonsense-mediated mRNA decay; autism; neuronal expression; X chromosome
• ISSN: 1359-4184; 1476-5578
• DOI: 10.1038/mp.2009.14

Mutations in the
UPF3B
gene, which encodes a protein involved in nonsense-mediated mRNA decay, have recently been described in four families with specific (Lujan–Fryns and FG syndromes), nonspecific X-linked mental retardation (XLMR) and autism. To further elucidate the contribution of
UPF3B
to mental retardation (MR), we screened its coding sequence in 397 families collected by the EuroMRX consortium. We identified one nonsense mutation, c.1081C>T/p.Arg361
*
, in a family with nonspecific MR (MRX62) and two amino-acid substitutions in two other, unrelated families with MR and/or autism (c.1136G>A/p.Arg379His and c.1103G>A/p.Arg368Gln). Functional studies using lymphoblastoid cell lines from affected patients revealed that c.1081C>T mutation resulted in
UPF3B
mRNA degradation and consequent absence of the UPF3B protein. We also studied the subcellular localization of the wild-type and mutated UPF3B proteins in mouse primary hippocampal neurons. We did not detect any obvious difference in the localization between the wild-type UPF3B and the proteins carrying the two missense changes identified. However, we show that UPF3B is widely expressed in neurons and also presents in dendritic spines, which are essential structures for proper neurotransmission and thus learning and memory processes. Our results demonstrate that in addition to Lujan–Fryns and FG syndromes, UPF3B protein truncation mutations can cause also nonspecific XLMR. We also identify comorbidity of MR and autism in another family with
UPF3B
mutation. The neuronal localization pattern of the UPF3B protein and its function in mRNA surveillance suggests a potential function in the regulation of the expression and degradation of various mRNAs present at the synapse.