软骨发育不全(ACH),短肢骨骼发育不良最常见的形式,是由成纤维细胞生长因子受体3(FGFR3)基因的功能获得突变引起的。超过97%的患者由FGFR3基因中的杂合子p.G380R突变产生。我们在这里展示了一个孩子,他在FGFR3的同一等位基因上有两个从头变异,一个常见的p.G380R突变和一个新的p.S378N变体。
一名3岁的日本女孩出生在非近亲健康的父母身上,其临床和放射学表型比经典的ACH更为严重。包括严重的短肢身材矮小,干phy端和骨phy骨明显骨化缺陷,由于大孔狭窄导致的脑积水和颈髓腔压迫,肺发育不全,以及总电机发展的显著延迟。从先证中提取基因组DNA并进行全外显子组测序。随后通过Sanger测序确认变体。
突变分析表明先证者在FGFR3基因中具有p.S378N(c.1133G>A)和p.G380R(c.1138G>A)变体。在她的父母中未检测到这两种变体,因此认为是从头的。开发等位基因特异性PCR以确定这些突变是在相同等位基因上(顺式)还是在不同等位基因上(反式)。在用突变体1133A的引物产生的PCR产物中发现了c.1138G>A突变,但在野生型1133G的产品中未检测到,确认p.S378N和p.G380R变体位于相同的等位基因上(顺式)。
这是第二种情况,在同一等位基因上的跨膜结构域中具有两个FGFR3变体。p.S378N变体可以对具有p.G380R突变的激活受体提供累加效应,并改变蛋白质功能,这可能是造成本案严重表型的原因。
Achondroplasia (ACH), the most common form of short-limbed skeletal dysplasia, is caused by gain-of-function mutations in the fibroblast growth factor receptor 3 (FGFR3) gene. More than 97% of patients result from a heterozygous p.G380R mutation in the FGFR3 gene. We present here a child who had two de novo variants in the FGFR3 on the same allele, a common p.G380R mutation and a novel p.S378N variant.
A 3-year-old Japanese girl born from non-consanguineous healthy parents showed more severe clinical and radiological phenotypes than classic ACH, including severe short-limbed short stature with marked ossification defects in the metaphysis and epiphysis, hydrocephalus and cervicomedullary compression due to foramen magnum stenosis, prolonged pulmonary hypoplasia, and significant delay in the gross motor development. Genomic DNA was extracted from the proband and whole-exome sequencing was performed. The variants were subsequently confirmed by Sanger sequencing.
Mutation analysis demonstrated that the proband had p.S378N (c.1133G>A) and p.G380R (c.1138G>A) variants in the FGFR3 gene. Both variants were not detected in her parents and therefore considered de novo. An allele-specific PCR was developed in order to determine whether these mutations were on the same allele (cis) or on different alleles (trans). The c.1138G>A mutation was found in the PCR product generated with the primer for the mutant 1133A, but it was not detected in the product with the wild-type 1133G, confirming that p.S378N and p.G380R variants were located on the same allele (cis).
This is the second
case who had two FGFR3 variants in the transmembrane domain on the same allele. The p.S378N variant may provide an additive effect on the activating receptor with the p.G380R mutation and alter the protein function, which could be responsible for the severe phenotype of the present
case.