The 22q11.2 deletion syndrome (22q11DS) is associated with a wide spectrum of cognitive and psychiatric symptoms. Despite the considerable work performed over the past 20 years, the genetic etiology of the neurodevelopmental phenotype remains speculative. Here, we report de novo heterozygous truncating variants in the HIRA (Histone cell cycle regulation defective, S. Cerevisiae, homolog of, A) gene associated with a neurodevelopmental disorder in two unrelated patients. HIRA is located within the commonly deleted region of the 22q11DS and encodes a histone chaperone that regulates neural progenitor proliferation and neurogenesis, and that belongs to the WD40 Repeat (WDR) protein family involved in brain development and neuronal connectivity. To address the specific impact of HIRA haploinsufficiency in the neurodevelopmental phenotype of 22q11DS, we combined Hira knock-down strategies in developing mouse primary hippocampal neurons, and the direct study of brains from heterozygous Hira^+/− mice. Our in vitro analyses revealed that Hira gene is mostly expressed during neuritogenesis and early dendritogenesis stages in mouse total brain and in developing primary hippocampal neurons. Moreover, shRNA knock-down experiments showed that a twofold decrease of endogenous Hira expression level resulted in an impaired dendritic growth and branching in primary developing hippocampal neuronal cultures. In parallel, in vivo analyses demonstrated that Hira^+/− mice displayed subtle neuroanatomical defects including a reduced size of the hippocampus, the fornix and the corpus callosum. Our results suggest that HIRA haploinsufficiency would likely contribute to the complex pathophysiology of the neurodevelopmental phenotype of 22q11DS by impairing key processes in neurogenesis and by causing neuroanatomical defects during cerebral development.

22q11.2缺失综合征（22q11DS）与广泛的认知和精神症状相关。尽管在过去的20年中进行了大量工作，但神经发育表型的遗传病因仍是推测性的。在这里，我们报道了与两名不相关患者的神经发育障碍相关的HIRA（组蛋白细胞周期调控缺陷，酿酒酵母，A的同源物）基因的从头杂合截短变体。HIRA位于22q11DS的通常缺失区域内，编码组蛋白伴侣，它调节神经祖细胞的增殖和神经发生，并且属于参与大脑发育和神经元连接的WD40重复（WDR）蛋白家族。解决特定的影响HIRA在22q11DS的神经发育表型中存在单倍不足，我们结合了开发小鼠原代海马神经元中的Hira敲低策略以及对杂合Hira ^+/-小鼠大脑的直接研究。我们的体外分析显示，Hira基因主要在小鼠全脑和发育中的原代海马神经元的神经形成和早期树突形成阶段表达。此外，shRNA敲低实验表明内源性Hira表达水平的两倍降低导致原代发育的海马神经元培养物中树突状生长和分支受损。同时，体内分析表明Hira ^+/-小鼠表现出细微的神经解剖学缺陷，包括海马，穹and和call体尺寸减小。我们的研究结果表明，HIRA单倍体功能不足可能通过损害神经发生的关键过程并在大脑发育过程中引起神经解剖缺陷，从而促进22q11DS神经发育表型的复杂病理生理。