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


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.

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We thank the patients and their family members, the XLMR European Consortium for their participation in this study. We also thank Rose-Anne Thépault, Brigitte Jauffrion and Lucianne Vandeleur for help with sequencing reactions and cell culture. This work was supported by grants from Institut National de la Santé et de la Recherche Médicale (INSERM) and the University of Tours, by the European Union (grant QLG3-CT-2002-01810), by Australian NHMRC Project grant 453457 (JG) and senior research fellowship (JG).

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Correspondence to F Laumonnier.

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Laumonnier, F., Shoubridge, C., Antar, C. et al. Mutations of the UPF3B gene, which encodes a protein widely expressed in neurons, are associated with nonspecific mental retardation with or without autism. Mol Psychiatry 15, 767–776 (2010).

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  • autism
  • mental retardation
  • nonsense-mediated mRNA decay
  • neuronal expression
  • X chromosome

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