The study of consanguineous families has provided novel insights into genetic causes of monogenic parkinsonism. Here, we present a family from the rural Khyber Pakhtunkhwa province, Pakistan, where three siblings were diagnosed with early-onset parkinsonism. Homozygosity mapping of two affected siblings and three unaffected family members identified two candidate autozygous loci segregating with disease, 8q24.12-8q24.13 and 9q31.2-q33.1. Whole-exome sequence analysis identified a single rare homozygous missense sequence variant within this region, CCN3 p.D82G. Although unaffected family members were heterozygous for this putative causal mutation, it was absent in 3,222 non-Parkinson's disease (PD) subjects of Pakistani heritage. Screening of 353 Australian PD cases, including 104 early-onset cases and 57 probands from multi-incident families, also did not identify additional carriers. Overexpression of wild-type and the variant CCN3 constructs in HEK293T cells identified an impaired section of the variant protein, alluding to potential mechanisms for disease. Further, qPCR analysis complemented previous microarray data suggesting mRNA expression of CCN3 was downregulated in unrelated sporadic PD cases when compared to unaffected subjects. These data indicate a role for CCN3 in parkinsonism, both in this family as well as sporadic PD cases; however, the specific mechanisms require further investigation. Additionally, further screening of the rural community where the family resided is warranted to assess the local frequency of the variant. Overall, this study highlights the value of investigating underrepresented and isolated affected families for novel putative parkinsonism genes.

中文翻译：

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隐性遗传的CCN3突变是早期帕金森病的罕见原因的证据。

对近亲家庭的研究为单基因帕金森病的遗传原因提供了新颖的见解。在这里，我们介绍了一个来自巴基斯坦开伯尔-普赫图赫瓦省农村的家庭，那里有3个兄弟姐妹被诊断患有早发性帕金森病。两个受影响的兄弟姐妹和三个未受影响的家庭成员的纯合子作图确定了两个候选的纯合子位点，分别与疾病分别为8q24.12-8q24.13和9q31.2-q33.1。全外显子序列分析确定了在该区域CCN3 p.D82G中的单个罕见的纯合错义序列变体。尽管未受影响的家庭成员对该假定的因果突变是杂合的，但在巴基斯坦传统的3,222例非帕金森氏病（PD）受试者中却没有。筛选了353例澳大利亚PD病例，包括104例早发病例和来自多事件家庭的57个先证者，也没有确定其他运营商。HEK293T细胞中野生型和变异CCN3构建体的过表达确定了变异蛋白的受损部分，暗示了疾病的潜在机制。此外，qPCR分析补充了以前的微阵列数据，表明与不受影响的受试者相比，在无关的散发性PD患者中CCN3的mRNA表达下调。这些数据表明CCN3在帕金森病中的作用，在该家族以及偶发的PD病例中均如此。但是，具体机制尚需进一步研究。另外，有必要进一步筛选该家庭所居住的农村社区，以评估该变体的当地发生率。总的来说，这项研究强调了调查代表性不足和孤立的受影响家庭对新型推定帕金森病基因的价值。