Mutations in the Small GTPase Gene RAB39B Are Responsible for X-linked Mental Retardation Associated with Autism, Epilepsy, and Macrocephaly

Maila Giannandrea, Veronica Bianchi, Maria Lidia Mignogna, Alessandra Sirri, Salvatore Carrabino, Errico D'Elia, Matteo Vecellio, Silvia Russo, Francesca Cogliati, Lidia Larizza, Hans Hilger Ropers, Andreas Tzschach, Vera Kalscheuer, Barbara Oehl-Jaschkowitz, Cindy Skinner, Charles E. Schwartz, Jozef Gecz, Hilde Van Esch, Martine Raynaud, Jamel ChellyArjan P M de Brouwer, Daniela Toniolo, Patrizia D'Adamo

Research output: Contribution to journalArticlepeer-review


Human Mental Retardation (MR) is a common and highly heterogeneous pediatric disorder affecting around 3% of the general population; at least 215 X-linked MR (XLMR) conditions have been described, and mutations have been identified in 83 different genes, encoding proteins with a variety of function, such as chromatin remodeling, synaptic function, and intracellular trafficking. The small GTPases of the RAB family, which play an essential role in intracellular vesicular trafficking, have been shown to be involved in MR. We report here the identification of mutations in the small GTPase RAB39B gene in two male patients. One mutation in family X (D-23) introduced a stop codon seven amino acids after the start codon (c.21C > A; p.Y7X). A second mutation, in the MRX72 family, altered the 5′ splice site (c.215+1G > A) and normal splicing. Neither instance produced a protein. Mutations segregate with the disease in the families, and in some family members intellectual disabilities were associated with autism spectrum disorder, epileptic seizures, and macrocephaly. We show that RAB39B, a novel RAB GTPase of unknown function, is a neuronal-specific protein that is localized to the Golgi compartment. Its downregulation leads to an alteration in the number and morphology of neurite growth cones and a significant reduction in presynaptic buttons, suggesting that RAB39B is required for synapse formation and maintenance. Our results demonstrate developmental and functional neuronal alteration as a consequence of downregulation of RAB39B and emphasize the critical role of vesicular trafficking in the development of neurons and human intellectual abilities.

Original languageEnglish
Pages (from-to)185-195
Number of pages11
JournalAmerican Journal of Human Genetics
Issue number2
Publication statusPublished - Feb 12 2010

ASJC Scopus subject areas

  • Genetics
  • Genetics(clinical)


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