Department of Neurology, The Second Hospital of Dalian Medical University, Dalian, China.
Center for Reproductive and Genetic Medicine, Dalian Municipal Women and Children's Medical Center, Dalian, China.
Mol Genet Genomic Med. 2020 Jun;8(6):e1235. doi: 10.1002/mgg3.1235. Epub 2020 Apr 7.
Asparagine synthetase deficiency (ASNSD) is a rare pediatric congenital disorder that clinically manifests into severe progressive microcephaly, global developmental delay, spastic quadriplegia, and refractory seizures. ASNSD is caused by inheritable autosomal recessive mutations in the asparagine synthetase (ASNS) gene.
We performed whole-exome sequencing using the patient's peripheral blood, and newly discovered mutations were subsequently verified in the patient's parents via Sanger sequencing. Software-based bioinformatics analyses (protein sequence conservation analysis, prediction of protein phosphorylation sites, protein structure modeling, and protein stability prediction) were performed to investigate and deduce their downstream effects.
In this article, we summarized all the previously reported cases of ASNSD and that of a Chinese girl who was clinically diagnosed with ASNSD, which was later confirmed via genetic testing. Whole-exome sequencing revealed two compound heterozygous missense mutations within the ASNS (c.368T > C, p.F123S and c.1649G > A, p.R550H). The origin of the two mutations was also verified in the patient's parents via Sanger sequencing. The mutation c.368T > C (p.F123S) was discovered and confirmed to be novel and previously unreported. Using software-based bioinformatics analyses, we deduced that the two mutation sites are highly conserved across a wide range of species, with the ability to alter different phosphorylation sites and destabilize the ASNS protein structure. The newly identified p.F123S mutation was predicted to be the most significantly destabilizing and detrimental mutation to the ASNS protein structure, compared to all other previously reported mutations.
Evidently, the presence of these compound heterozygous mutations could lead to severe clinical phenotypes and serve as a potential indicator for considerably higher risk with less optimistic prognosis in ASNSD patients.
天冬酰胺合成酶缺乏症（ASNSD）是一种罕见的儿科先天性疾病，临床上表现为严重进行性小头畸形、全面发育迟缓、痉挛性四肢瘫痪和难治性癫痫。ASNSD 是由天冬酰胺合成酶（ASNS）基因的可遗传常染色体隐性突变引起的。
我们使用患者的外周血进行全外显子组测序，随后通过 Sanger 测序在患者的父母中验证新发现的突变。通过基于软件的生物信息学分析（蛋白质序列保守性分析、蛋白质磷酸化位点预测、蛋白质结构建模和蛋白质稳定性预测）来研究和推断其下游影响。
本文总结了所有先前报道的 ASNSD 病例和一名被临床诊断为 ASNSD 的中国女孩的病例，该病例后来通过基因测试得到证实。全外显子组测序显示 ASNS 中存在两个复合杂合错义突变（c.368T>C，p.F123S 和 c.1649G>A，p.R550H）。通过 Sanger 测序也在患者的父母中验证了这两个突变的来源。突变 c.368T>C（p.F123S）是新发现的，并且之前没有报道过。通过基于软件的生物信息学分析，我们推断这两个突变位点在广泛的物种中高度保守，能够改变不同的磷酸化位点并使 ASNS 蛋白质结构不稳定。与所有其他先前报道的突变相比，新鉴定的 p.F123S 突变被预测对 ASNS 蛋白质结构的破坏性最大。
显然，这些复合杂合突变的存在可能导致严重的临床表型，并可能成为 ASNSD 患者风险更高、预后更不乐观的潜在指标。
