1 Paediatric Neurology and Neurogenetics Unit and Laboratories, A. Meyer Children's Hospital - Department of Neuroscience, Pharmacology and Child Health, University of Florence, 50139, Florence, Italy.
Brain. 2013 Nov;136(Pt 11):3378-94. doi: 10.1093/brain/awt249. Epub 2013 Sep 20.
Periventricular nodular heterotopia is caused by defective neuronal migration that results in heterotopic neuronal nodules lining the lateral ventricles. Mutations in filamin A (FLNA) or ADP-ribosylation factor guanine nucleotide-exchange factor 2 (ARFGEF2) cause periventricular nodular heterotopia, but most patients with this malformation do not have a known aetiology. Using comparative genomic hybridization, we identified 12 patients with developmental brain abnormalities, variably combining periventricular nodular heterotopia, corpus callosum dysgenesis, colpocephaly, cerebellar hypoplasia and polymicrogyria, harbouring a common 1.2 Mb minimal critical deletion in 6q27. These anatomic features were mainly associated with epilepsy, ataxia and cognitive impairment. Using whole exome sequencing in 14 patients with isolated periventricular nodular heterotopia but no copy number variants, we identified one patient with periventricular nodular heterotopia, developmental delay and epilepsy and a de novo missense mutation in the chromosome 6 open reading frame 70 (C6orf70) gene, mapping in the minimal critical deleted region. Using immunohistochemistry and western blots, we demonstrated that in human cell lines, C6orf70 shows primarily a cytoplasmic vesicular puncta-like distribution and that the mutation affects its stability and subcellular distribution. We also performed in utero silencing of C6orf70 and of Phf10 and Dll1, the two additional genes mapping in the 6q27 minimal critical deleted region that are expressed in human and rodent brain. Silencing of C6orf70 in the developing rat neocortex produced periventricular nodular heterotopia that was rescued by concomitant expression of wild-type human C6orf70 protein. Silencing of the contiguous Phf10 or Dll1 genes only produced slightly delayed migration but not periventricular nodular heterotopia. The complex brain phenotype observed in the 6q terminal deletion syndrome likely results from the combined haploinsufficiency of contiguous genes mapping to a small 1.2 Mb region. Our data suggest that, of the genes within this minimal critical region, C6orf70 plays a major role in the control of neuronal migration and its haploinsufficiency or mutation causes periventricular nodular heterotopia.
室管膜下结节性异位是由于神经元迁移缺陷导致的，其结果是异位神经元结节沿侧脑室排列。细丝蛋白 A (FLNA) 或 ADP-核糖基化因子鸟嘌呤核苷酸交换因子 2 (ARFGEF2) 的突变会导致室管膜下结节性异位，但大多数患有这种畸形的患者没有已知的病因。使用比较基因组杂交技术，我们鉴定了 12 名患有发育性脑异常的患者，这些患者存在室管膜下结节性异位、胼胝体发育不良、尖头畸形、小脑发育不良和多小脑回等多种病变，共同携带 6q27 上的一个 1.2Mb 最小关键缺失。这些解剖特征主要与癫痫、共济失调和认知障碍有关。在 14 名孤立性室管膜下结节性异位但没有拷贝数变异的患者中进行全外显子测序，我们发现 1 名患者患有室管膜下结节性异位、发育迟缓、癫痫和染色体 6 开放阅读框 70 (C6orf70) 基因的新生错义突变，该突变位于最小关键缺失区域内。通过免疫组化和 Western blot，我们证明在人类细胞系中，C6orf70 主要表现为细胞质囊泡点状分布，该突变影响其稳定性和亚细胞分布。我们还在体内沉默了 C6orf70 以及 Phf10 和 Dll1 基因，这两个基因也位于 6q27 最小关键缺失区域内，在人和啮齿动物大脑中均有表达。在发育中的大鼠新皮质中沉默 C6orf70 会导致室管膜下结节性异位，而同时表达野生型人类 C6orf70 蛋白可以挽救这种异位。沉默相邻的 Phf10 或 Dll1 基因只会导致稍微延迟的迁移，而不会导致室管膜下结节性异位。6q 端粒缺失综合征中观察到的复杂脑表型可能是由于映射到一个 1.2Mb 小区域的连续基因的复合杂合性缺失所致。我们的数据表明，在这个最小关键区域内的基因中，C6orf70 在控制神经元迁移中起主要作用，其杂合性缺失或突变导致室管膜下结节性异位。
