Waguespack Steven G, Koller Daniel L, White Kenneth E, Fishburn Tonya, Carn Gwenaelle, Buckwalter Kenneth A, Johnson Michelle, Kocisko Maureen, Evans Wayne E, Foroud Tatiana, Econs Michael J
Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA.
J Bone Miner Res. 2003 Aug;18(8):1513-8. doi: 10.1359/jbmr.2003.18.8.1513.
ADO2 is an uncommon sclerosing bone disorder with incomplete penetrance and variable expressivity. Positional candidate studies were performed to identify the gene responsible for ADO2. In 11 of 12 kindreds, five different missense mutations were identified in the ClCN7 gene, indicating the genetic basis and possible dominant negative mechanism for ADO2.
Autosomal dominant osteopetrosis, type II (ADO2) is an uncommon sclerosing bone disorder with a distinct radiographic appearance and unique clinical characteristics. We present the results from our genetic studies designed to identify the ADO2 gene through a positional candidate approach.
Having identified 12 families with ADO2, we initially performed linkage studies in our seven largest kindreds and observed a summed maximum LOD score of 15.91 at marker D16S521 on chromosome 16p13.3. Critical meiotic recombination events further narrowed the putative gene region to a 7.6-cM area, which contains the candidate genes ATP6L and chloride channel 7 (ClCN7). We screened affected individuals from each ADO2 family for mutations in these genes using direct sequencing. Identified mutations were subsequently confirmed through direct sequencing or restriction fragment length polymorphism analysis. We then calculated the overall disease penetrance rate after all available at-risk family members were assessed for ClCN7 gene mutations.
No ATP6L mutations were identified in affected subjects. Subsequently, as CICN7 gene mutations were being reported, we identified two novel (L213F, R762L) and three known (G215R, R286W, R767W) missense mutations in 11 kindreds. In our large sample, disease penetrance was 66% (62 clinically affected individuals/94 subjects with the gene mutation). To date, nine different mutations have been discovered in the ClCN7 gene in 22 of 23 ADO2 families studied.
We conclude that mutations in the CICN7 gene are responsible for ADO2 and that genetic heterogeneity is unlikely to exist in this disorder. Based on the preponderance of missense mutations and the knowledge that chloride channels probably function as dimers, it seems that heterozygous ClCN7 gene mutations may cause ADO2 through a dominant negative mechanism.
ADO2是一种罕见的硬化性骨病，具有不完全外显率和可变表达性。进行了定位候选研究以确定导致ADO2的基因。在12个家族中的11个中，在ClCN7基因中鉴定出5种不同的错义突变，这表明了ADO2的遗传基础和可能的显性负性机制。
常染色体显性遗传性骨硬化症II型（ADO2）是一种罕见的硬化性骨病，具有独特的影像学表现和独特的临床特征。我们展示了通过定位候选方法鉴定ADO2基因的遗传研究结果。
在确定了12个患有ADO2的家族后，我们首先在7个最大的家族中进行连锁研究，在16号染色体16p13.3上标记D16S521处观察到累计最大LOD分数为15.91。关键的减数分裂重组事件进一步将推定的基因区域缩小到7.6厘摩的区域，该区域包含候选基因ATP6L和氯离子通道7（ClCN7）。我们使用直接测序法筛选每个ADO2家族中受影响个体的这些基因中的突变。随后通过直接测序或限制性片段长度多态性分析确认鉴定出的突变。然后在评估了所有可获得的有风险家庭成员的ClCN7基因突变后计算总体疾病外显率。
在受影响的受试者中未鉴定出ATP6L突变。随后，随着CICN7基因突变的报道，我们在11个家族中鉴定出2种新的（L213F，R762L）和3种已知的（G215R，R286W，R767W）错义突变。在我们的大样本中，疾病外显率为66%（62名临床受影响个体/94名有基因突变的受试者）。迄今为止，在23个研究的ADO2家族中的22个中，已在ClCN7基因中发现9种不同的突变。
我们得出结论，CICN7基因突变是导致ADO2的原因，并且这种疾病不太可能存在遗传异质性。基于错义突变的优势以及氯离子通道可能以二聚体形式发挥作用的知识，似乎杂合的ClCN7基因突变可能通过显性负性机制导致ADO2。
