Paget's disease of bone (PDB) is a late‐onset disorder frequently caused by mutations in the SQSTM1 gene, leading to hyperactive osteoclasts and resulting in bone pain, deformities, and fractures. However, some more severe forms of PDB—negative for SQSTM1 mutations—have been described, in which the disease degenerates into bone cancers and shows a poor prognosis. Osteosarcoma is the most frequent and aggressive tumor arising in PDB (OS/PDB), with a 5‐year survival rate almost nil, but the underlying molecular mechanism is unknown. Here, we investigated an extended pedigree with 11 individuals affected by early onset and polyostotic PDB, mainly interesting the appendicular skeleton. Interestingly, three members also developed secondary osteosarcoma. We performed exome sequencing and identified a 4‐bp deletion in the PFN1 gene, resulting in the degradation of the mutant protein. Copy number screening on 218 PDB individuals of our biobank disclosed that four of them (~2%) carry a germline heterozygous deletion of PFN1. The identification of these subjects, who exhibit a particularly severe form of disease, emphasizes the diagnostic value of this genetic screening to identify PDB individuals predisposed to develop osteosarcoma. In fact, we detected allelic imbalance at PFN1 locus also in 8 of 14 (57%) sporadic OS/PDB, further proving its causative role. in vitro experiments also confirmed PFN1 involvement in this form of PDB. Indeed, CRISPR‐Cas9‐mediated Pfn1 knockout in pre‐osteoclasts resulted into enhanced osteoclast differentiation and resorption, with the formation of large osteoclasts never described before in PDB. In addition, Pfn1 lacking pre‐osteoblasts lost their differentiation capability and failed to efficiently mineralize bone. Moreover, they acquired features of malignant transformation, including loss of focal adhesions and increased invasion ability. In conclusion, these findings disclose PFN1 haploinsufficiency as the pathological mechanism in OS/PDB. © 2020 American Society for Bone and Mineral Research.

中文翻译：

---

Profilin 1 的缺失导致早发性佩吉特骨病。

佩吉特骨病 (PDB) 是一种迟发性疾病，通常由SQSTM1基因突变引起，导致破骨细胞过度活跃并导致骨痛、畸形和骨折。然而，一些更严重的 PDB 形式——对SQSTM1是阴性的突变——已被描述，其中疾病退化为骨癌并显示出不良预后。骨肉瘤是 PDB (OS/PDB) 中最常见和最具侵袭性的肿瘤，5 年生存率几乎为零，但潜在的分子机制尚不清楚。在这里，我们调查了 11 名受早发性多骨性 PDB 影响的个体的扩展谱系，主要关注阑尾骨骼。有趣的是，三名成员还患上了继发性骨肉瘤。我们进行了外显子组测序，发现PFN1基因中有一个 4 bp 的缺失，导致突变蛋白降解。对我们生物库的 218 个 PDB 个体的拷贝数筛选显示，其中 4 个（约 2%）携带PFN1的种系杂合缺失. 对这些表现出特别严重疾病形式的受试者的识别强调了这种基因筛查在识别易患骨肉瘤的 PDB 个体方面的诊断价值。事实上，我们还在 14 个（57%）散发性 OS/PDB 中的 8 个中检测到PFN1基因座的等位基因失衡，进一步证明了其致病作用。体外实验也证实了PFN1参与了这种形式的 PDB。事实上，CRISPR-Cas9 介导的前破骨细胞Pfn1敲除导致破骨细胞分化和吸收增强，在 PDB 中形成了以前从未描述过的大破骨细胞。此外，Pfn1缺乏前成骨细胞失去了它们的分化能力，不能有效地矿化骨骼。此外，他们获得了恶变的特征，包括粘着斑丧失和侵袭能力增加。总之，这些发现揭示了 PFN1 单倍体不足是 OS/PDB 的病理机制。© 2020 美国骨与矿物研究学会。