Division of Neuropathology, Department of Pathology, Brigham and Women's Hospital, Boston, MA, USA.
Division of Genetics and Genomics, Department of Pediatrics, Boston Children's Hospital, Boston, MA, USA.
Acta Neuropathol. 2024 Jul 24;148(1):10. doi: 10.1007/s00401-024-02774-2.
Creutzfeldt-Jakob Disease (CJD), the most common human prion disease, is associated with pathologic misfolding of the prion protein (PrP), encoded by the PRNP gene. Of human prion disease cases, < 1% were transmitted by misfolded PrP, ~ 15% are inherited, and ~ 85% are sporadic (sCJD). While familial cases are inherited through germline mutations in PRNP, the cause of sCJD is unknown. Somatic mutations have been hypothesized as a cause of sCJD, and recent studies have revealed that somatic mutations accumulate in neurons during aging. To investigate the hypothesis that somatic mutations in PRNP may underlie sCJD, we performed deep DNA sequencing of PRNP in 205 sCJD cases and 170 age-matched non-disease controls. We included 5 cases of Heidenhain variant sporadic CJD (H-sCJD), where visual symptomatology and neuropathology implicate localized initiation of prion formation, and examined multiple regions across the brain including in the affected occipital cortex. We employed Multiple Independent Primer PCR Sequencing (MIPP-Seq) with a median depth of > 5000× across the PRNP coding region and analyzed for variants using MosaicHunter. An allele mixing experiment showed positive detection of variants in bulk DNA at a variant allele fraction (VAF) as low as 0.2%. We observed multiple polymorphic germline variants among individuals in our cohort. However, we did not identify bona fide somatic variants in sCJD, including across multiple affected regions in H-sCJD, nor in control individuals. Beyond our stringent variant-identification pipeline, we also analyzed VAFs from raw sequencing data, and observed no evidence of prion disease enrichment for the known germline pathogenic variants P102L, D178N, and E200K. The lack of PRNP pathogenic somatic mutations in H-sCJD or the broader cohort of sCJD suggests that clonal somatic mutations may not play a major role in sporadic prion disease. With H-sCJD representing a localized presentation of neurodegeneration, this serves as a test of the potential role of clonal somatic mutations in genes known to cause familial neurodegeneration.
克雅氏病（CJD）是最常见的人类朊病毒病，与朊病毒蛋白（PrP）的病理性错误折叠有关，该蛋白由 PRNP 基因编码。在人类朊病毒病病例中，<1%是由错误折叠的 PrP 传播的，15%是遗传性的，85%是散发性的（sCJD）。家族性病例是通过 PRNP 中的种系突变遗传的，而 sCJD 的原因尚不清楚。体细胞突变已被假设为 sCJD 的原因，最近的研究表明，体细胞突变在衰老过程中会在神经元中积累。为了研究 PRNP 中的体细胞突变是否可能是 sCJD 的基础这一假说，我们对 205 例 sCJD 病例和 170 名年龄匹配的非疾病对照进行了 PRNP 的深度 DNA 测序。我们包括 5 例海登海因变异散发性克雅氏病（H-sCJD），其中视觉症状和神经病理学提示朊病毒形成的局部起始，并检查了大脑的多个区域，包括受影响的枕叶皮层。我们采用了多发性独立引物 PCR 测序（MIPP-Seq），在 PRNP 编码区的中位数深度>5000×，并使用 MosaicHunter 对变体进行了分析。等位基因混合实验显示，在变异等位基因分数（VAF）低至 0.2%的情况下，在散装 DNA 中可以检测到阳性变体。我们在队列中的个体中观察到多个多态性种系变体。然而，我们没有在 sCJD 中发现真正的体细胞变体，包括在 H-sCJD 的多个受影响区域，也没有在对照个体中发现。除了我们严格的变体识别管道之外，我们还分析了原始测序数据的 VAFs，没有观察到已知种系致病性变体 P102L、D178N 和 E200K 的朊病毒病富集证据。在 H-sCJD 或更广泛的 sCJD 队列中没有 PRNP 致病性体细胞突变表明，克隆体细胞突变可能在散发性朊病毒病中不起主要作用。由于 H-sCJD 代表神经退行性变的局部表现，这是对已知导致家族性神经退行性变的基因中克隆体细胞突变潜在作用的检验。
