Cytogenetics Laboratory, Scientific Institute E. Medea, Bosisio Parini, Italy.
PLoS Genet. 2011 Jul;7(7):e1002173. doi: 10.1371/journal.pgen.1002173. Epub 2011 Jul 14.
In this study, we used deletions at 22q13, which represent a substantial source of human pathology (Phelan/McDermid syndrome), as a model for investigating the molecular mechanisms of terminal deletions that are currently poorly understood. We characterized at the molecular level the genomic rearrangement in 44 unrelated patients with 22q13 monosomy resulting from simple terminal deletions (72%), ring chromosomes (14%), and unbalanced translocations (7%). We also discovered interstitial deletions between 17-74 kb in 9% of the patients. Haploinsufficiency of the SHANK3 gene, confirmed in all rearrangements, is very likely the cause of the major neurological features associated with PMS. SHANK3 mutations can also result in language and/or social interaction disabilities. We determined the breakpoint junctions in 29 cases, providing a realistic snapshot of the variety of mechanisms driving non-recurrent deletion and repair at chromosome ends. De novo telomere synthesis and telomere capture are used to repair terminal deletions; non-homologous end-joining or microhomology-mediated break-induced replication is probably involved in ring 22 formation and translocations; non-homologous end-joining and fork stalling and template switching prevail in cases with interstitial 22q13.3. For the first time, we also demonstrated that distinct stabilizing events of the same terminal deletion can occur in different early embryonic cells, proving that terminal deletions can be repaired by multistep healing events and supporting the recent hypothesis that rare pathogenic germline rearrangements may have mitotic origin. Finally, the progressive clinical deterioration observed throughout the longitudinal medical history of three subjects over forty years supports the hypothesis of a role for SHANK3 haploinsufficiency in neurological deterioration, in addition to its involvement in the neurobehavioral phenotype of PMS.
在这项研究中，我们使用了 22q13 的缺失，这代表了人类病理学的一个重要来源（Phelan/McDermid 综合征），作为研究目前了解甚少的末端缺失的分子机制的模型。我们从分子水平上对 44 名 22q13 单体患者的基因组重排进行了特征描述，这些患者的 22q13 单体是由简单末端缺失（72%）、环状染色体（14%）和不平衡易位（7%）引起的。我们还发现 9%的患者存在 17-74kb 的中间缺失。在所有重排中，SHANK3 基因的单倍不足很可能是与 PMS 相关的主要神经特征的原因。SHANK3 突变也可能导致语言和/或社交互动障碍。我们确定了 29 例病例的断点连接，为驱动染色体末端非重复缺失和修复的各种机制提供了现实的快照。从头端粒合成和端粒捕获用于修复末端缺失；非同源末端连接或微同源介导的断裂诱导复制可能参与了 22 号环的形成和易位；非同源末端连接和叉停顿及模板转换在具有 22q13.3 中间缺失的病例中占主导地位。这是我们第一次证明，同一末端缺失的不同稳定事件可以发生在不同的早期胚胎细胞中，证明末端缺失可以通过多步修复事件来修复，并支持最近的假说，即罕见的致病性生殖系重排可能具有有丝分裂起源。最后，对三名受试者四十多年的纵向医学史进行的研究表明，SHANK3 单倍不足不仅与 PMS 的神经行为表型有关，而且还可能导致神经恶化。
