一例多种羧化酶缺乏症的HLCS基因变异分析

目的对1例临床诊断为多种羧化酶缺乏症(multiple carboxylase deficiency,MCD)的患儿及其父母进行相关致病基因的变异分析,为临床诊断及遗传咨询提供依据。方法应用PCR技术和DNA测序技术对患儿的MCD致病基因BT和HLCS编码区进行变异检测,并对患儿父母进行相应基因变异分析。在80名正常人中对未报道过的基因变异进行PCR-限制性片段长度多态性分析。结果患儿的BT基因编码区未发现碱基改变,HLCS基因存在c.286delG(p.Val96Leufs*162)和c.1648G>A(p.Val550Met)复合杂合变异,其中c.286delG(p.Val96Leufs*162)经PCR-限制性片段长度多态性分析验证为新变异。结论HLCS基因c.286delG(p.Val96Leufs*162)和c.1648G>A(p.Val550Met)变异可能为患儿的致病原因,致病基因的检出为临床诊断及遗传咨询提供了依据,同时丰富了HLCS基因变异谱。     

三例酪氨酸血症Ⅰ型患者的临床表现及基因突变分析

目的 分析酪氨酸血症Ⅰ型患儿的临床资料和基因突变情况,探讨基因型与临床表型的关系.方法 采用串联质谱检测血酪氨酸、苯丙氨酸和琥珀酰丙酮水平,气相质谱检测尿琥珀酰丙酮及有机酸,确诊酪氨酸血症工型,对确诊患儿进行基因突变检测分析.结果 确诊的3例患者中2例为急性型,1例为亚急性型,表现为肝肿大,血酪氨酸和琥珀酰丙酮显著增高.基因突变分析检测到5种突变类型:c.455G>A(W152X)、 c.520C>T(R174X)、c.974_976delCGAinsGC、c.1027 G>A(G343R)、c.1100 G>A(W367X),其中c.455G>A(W152X)、c.974_976delCGAinsGC、c.1100 G>A(W367X)为新突变.结论 应用串联质谱检测血酪氨酸及琥珀酰丙酮水平、气相质谱检测检测尿琥珀酰丙酮可诊断酪氨酸血症工型.基因突变检测结果为遗传咨询以及后续研究提供依据.     

新生儿筛查3-甲基巴豆酰辅酶A羧化酶缺乏症可疑患儿临床及基因突变分析

目的了解新生儿疾病筛查中疑诊为3-甲基巴豆酰辅酶A羧化酶缺乏症(MCCD)患儿的临床表现;分析3-甲基巴豆酰辅酶A羧化酶(MCC)基因突变类型。方法 2015年8月至2020年3月将在青岛市新生儿疾病筛查中心接受新生儿筛查,并疑诊为MCCD的11例患儿(男9例,女2例)纳入本研究,对所有患儿的生长发育等随访资料进行回顾分析;对部分可疑患儿进行MCC基因突变及尿气相色谱-质谱(GS/MS)检测,通过分析结果,预测青岛地区MCC基因突变谱。结果 (1)11例可疑患儿均无MCCD相关临床表现。11例可疑患儿中1例确诊为MCCD,有3例为母源性MCCD患儿,1例患儿排除MCCD。(2)本次共检出10种基因突变类型,其中MCCC1突变8种,分别为c.639+2TA、c.1225CT/p.R409X、c.945TC/p.Y315Y、c.626GT/p.G209V、c.863AG/p.E288G、c.227_228delTG/p.V76Gfs*4、c.1690delA和c.1075CA。MCCC2突变2种,为c.281+1GA和c.592CT/p.Q198*。经预测,本次检出的三种新突变c.626GT c.1075CA和c.281+1GA可能致病。结论 11例可疑患儿均无MCCD相关临床表现,本研究MCCC1突变多见,c.639+2TA突变可能为热点突变。     

一例异丁酰辅酶A脱氢酶缺乏症患儿的临床及基因变异分析

目的分析异丁酰辅酶A脱氢酶缺乏症患儿的临床和基因突变特点。方法收集1例新生儿串联质谱筛查发现的可疑异丁酰辅酶A脱氢酶缺乏症患儿的临床资料,采用基于高通量测序技术的基因Panel进行致病基因突变检测。结果串联质谱检测C4升高(波动于0.57～0.68μmol/L之间,参考值:0.08～0.43μmol/L),C4/C3升高(波动于0.44～0.73μmol/L,参考值0.05～0.39μmol/L),C4/C2升高(波动于0.04～0.07μmol/L,参考值0.01～0.04μmol/L),无特殊临床症状。基因检测示ACAD8基因第4外显子c.444GT(p.Pro148Pro)及第10外显子c.1166GA(p.Arg389Gln)复合杂合突变,其父携带c.444GT突变,其母携带c.1166GA突变。其中c.1166GA为文献未报道过的新突变。结论 ACAD8基因复合杂合突变是本例患儿的遗传学病因,新突变的检出丰富了基因突变谱。     

一个罕见的羧化全酶合成酶缺乏症家系的临床分析与基因诊断

目的对罕见的羧化全酶合成酶缺乏症患儿进行临床诊治和基因突变分析。方法结合临床表现,同时运用血串联质谱、尿气相色谱等,对1例婴儿期起病的疑似羧化全酶合成酶缺乏症/生物素酶缺乏症患儿进行筛查与初步诊断,并提取家系全部成员外周血DNA,应用聚合酶链反应(PCR)扩增生物素酶基因(BTD)的4个外显子和羧化全酶合成酶基因(HLCS)的12个外显子,直接测序,进行先证者及其他家系成员的基因突变检测,以明确患儿基因型与表型之间的关系。结果家系中患儿的发病时间均较早(第一胎男孩为2月+,第二胎女孩为1月),临床主要表现为出生后早期(1-2周)开始头部出现散在湿疹、脓疱疹,3个月时全身发红伴弥漫性浸润性丘疹和脱屑,营养不良貌,毛发稀黄,呼吸急促等。实验室检查发现轻度贫血、代谢性酸中毒,血串联质谱检测发现3-羟基异戊酰基肉碱(C5-OH)水平显著升高,尿有机酸分析显示尿乳酸、丙酮酸、羟基丙酸、丙酰甘氨酸、甲基巴豆酰甘氨酸等显著升高,符合羧化全酶合成酶缺乏症/生物素酶缺乏症的表现。突变检测:家系基因测序BTD基因未发现致病性突变,而在患儿HLCS基因的第9和第10号外显子上发现了致病性的突变位点:c.1522CT杂合突变和c.1711GA杂合突变,均为错义突变,50例健康人对照100个等位基因测序未发现这两个位点的突变。因此,患儿诊断明确。经生物素20mg/d补充治疗与营养干预后,患儿全身情况逐渐好转,2周后皮疹愈合,营养状况也逐渐得到改善。结论羧化全酶合成酶缺乏症以神经系统及皮肤损害、代谢性酸中毒为特征。串联质谱和气相色谱分析、基因突变分析有助于鉴别诊断和确诊,口服生物素疗效显著。本研究对一个羧化全酶合成酶缺乏症家系进行了临床分析和基因诊断,明确了患儿发病的遗传学病因,为这个家庭后面的产前诊断,打下了坚实的基础。     

八例原发性肉碱缺乏症基因突变分析北大核心CSCD

目的分析8例原发性肉碱缺乏症(systemic primary carnitine deficiency,CDSP)患者的SLC22A5基因突变情况。方法采用串联质谱技术对泉州地区77 511例样本进行遗传代谢病筛查,发现8例原发性肉碱缺乏症患者(其中有1例为母源性CDSP),应用MassArray技术结合Sanger测序法对CDSP患者SLC22A5基因突变位点进行检测,寻找可能的致病突变位点。对发现的新变异采用SIFT和PolyPhen-2进行蛋白功能预测。结果 8例患者均检测到SLC22A5基因突变,其中7例为复合杂合突变,1例为纯合突变。共发现6种突变类型,包括1种无义突变[c.760C>T(p.R254X)]和5种错义突变[c.51C>G(p.F17L)、c.250T>A(p.Y84N)、c.1195C>T(p.R399W)、c.1196G>A(p.R399Q)、c.1400C>G(p.S467C)]。其中,c.250T>A(p.Y84N)为SLC22A5基因新变异,新变异可能影响蛋白质的结构和功能。c.760C>T(p.R254X)突变频率最高,c.1400C>G(p.S467C)突变频率次之。结论本研究分析了8例原发性肉碱缺乏症患者的SLC22A5基因突变情况,从基因水平上证实了8例CDSP的诊断,发现了1个新的突变位点,丰富了SLC22A5基因的突变谱。     

多重扩增子高通量测序对高苯丙氨酸血症基因变异实验室检测效率的研究

目的 对高苯丙氨酸血症(hyperphenylalaninemia,HPA)干血片DNA样本进行多重扩增子高通量测序检测,研究该方法对HPA潜在病因的实验室诊断价值.方法 选取既往70例生化筛查为HPA的患儿干血片,提取DNA后使用覆盖126种遗传病130个基因的扩增子建库试剂盒建库,进行高通量测序和数据分析,获得样本基因变异信息.经一代测序验证位点准确性后,分析对样本具有诊断价值的变异位点信息进行疑似病因判定,评价高通量测序的检测和诊断效能.结果 高通量测序结果和既往部分样品的一代测序结果完全吻合.70例样本中,5例为PAH和PTPS纯合突变,53例检测出PAH或PTPS单个基因2～3个杂合突变位点,还有2例检出HPA信号通路相关的SPR基因或GCH 1基因各1个突变.检测结果中c.158G>A、c.728G>A、c.1068C>A、c.1238G>C、c.611A>G位点为PAH基因频率最高的5个突变.结论 通过高通量测序技术,可准确检测基因突变,提供病因解释,为后续召回和临床诊断提供重要参考.     

甲基丙二酸血症患儿MUT基因突变分析

目的 检测甲基丙二酸血症(methylmalonic acidemia,MMA)患儿MUT基因突变类型及突变频率,探讨基因型与临床表型之间的关系.方法 依据串联质谱检测血酰基肉碱、气相色谱-质谱检测尿甲基丙二酸以及维生素B_(12)负荷试验等,诊断21例单纯MMA患儿;采用聚合酶链反应和直接测序法对这些患儿进行MUT基因突变检测分析.结果 在21例单纯MMA患儿中14例检测到17种MUT基因突变,其中8种为未报道突变.以c.323G>A(R108H)、c.729_730insTT(D244LfsX39)与c.1630_1631GG>TA(G544X)较为常见,突变频率分别为14.3%、10.7%及14.3%,以错义突变多见(64.7%).14例MUT突变患儿中10例为早发型,1例为迟发型,3例由新生儿出生筛查检出;11例为维生素B_(12)无效型,3例为有效型.结论 揭示了中国MMA患儿中MUT基因的部分突变谱,MUT基因突变患儿发病较早,多为维生素B_(12)无效型.     

婴儿严重肌阵挛癫痫钠离子通道SCNIA基因突变分析

目的 研究婴儿严重肌阵挛癫痫(severe myoclonic epilepsy of infancy,SMEI)患儿钠离子通道a1亚单位基因(sodium channel al subunit gene,SCNIA)突变筛查及遗传特征.方法 收集SMEI患儿23例及其家系成员的临床资料及外周血DNA,采用PCR扩增和DNA直接测序的方法筛查SCNIA基因的26个外显子的突变.结果 23例SMEI患儿中17例有SCNlA基因突变.基因突变率约为73.9%(17/23),其中8例为错义突变(F90S、I91T、A239T、W952G、T1210K,V1335M、V1390M、G1433E),3例为无义突变(R612X、W768X、w1408X),3例为缺失突变(A395fsX400、L556fsX557、V1778fsX1800),1例为插入突变(Y1241fsX1270),1例为剪切部位突变(IVS10+3A>G),1例为同义突变(K1492K),截断突变约占总突变的47.1%(8/17).13个突变位点(F90S、I91T、T1210K、V1335M、G1433E、R612X、W768X,A395faX400、L556fsx557、V1778fsXl800、Y1241fsXl270、IVS10+3A>G、K1492K)经相关检索未见报道.14例突变已证实为新生突变,其余3例突变尚不能确定突变来源.结论 SCNIA基因是SMEI患儿的主要致病基因,约一半为截断突变.SMEI患儿的SCNIA基因突变无热点,且多为新生突变.     

新生儿短链酰基辅酶A脱氢酶缺乏症4例临床特征及基因突变分析

目的探讨青岛地区新生儿短链酰基辅酶A脱氢酶缺乏症(SCADD)患儿的临床特征及基因突变特点。方法利用串联质谱技术检测283 104名新生儿干血滤纸片中酰基肉碱水平,对筛查出的疑似SCADD患儿通过尿有机酸检测、短链酰基辅酶A脱氢酶(ACADS)突变检测进行确诊。结果共确诊4例短链酰基辅酶A脱氢酶缺乏症患儿,患病率1. 4/10万(1/70 776)。患儿临床表现无明显异常,串联质谱检测显示血丁酰基肉碱(C4)及其与乙酰肉碱(C2)、丙酰肉碱(C3)比值均增高。对4例患儿进行尿有机酸分析,乙基丙二酸均增高[8. 41～36. 34 mg/g肌酐(正常值0～6. 20 mg/g肌酐)],还有2例伴乳酸增高,1例伴丙酮酸增高。基因测序共发现7种ACADS突变,4种为已知突变,3种未报道突变,均为错义突变。4例患儿均为复合杂合突变,分别为:c. 1031AG/c. 989GA; c. 1186GA/c. 1195CT; c. 1031AG/c. 445AT; c. 1130CT/c. 1157GA。常见突变为c. 1031AG(25%),ACADS基因型与乙基丙二酸以及C4浓度水平无明显相关。对患儿进行饮食指导,随访均未出现临床症状,体格及智力发育正常。结论通过血串联质谱筛查配合基因测序可以对SCADD明确诊断,早期确诊的新生儿无临床症状,预后较好。     

Holocarboxylase synthetase deficiency: novel clinical and molecular findings

Tammachote R, Janklat S, Tongkobpetch S, Suphapeetiporn K and Shotelersuk V. Holocarboxylase synthetase deficiency: novel clinical and molecular findings. Multiple carboxylase deficiency (MCD) is an autosomal recessive metabolic disorder caused by defective activity of biotinidase or holocarboxylase synthetase (HLCS) in the biotin cycle. Clinical symptoms include skin lesions and severe metabolic acidosis. Here, we reported four unrelated Thai patients with MCD, diagnosed by urine organic acid analysis. Unlike Caucasians, which biotinidase deficiency has been found to be more common, all of our four Thai patients were affected by HLCS deficiency. Instead of the generally recommended high dose of biotin, our patients were given biotin at 1.2 mg/day. This low‐dose biotin significantly improved their clinical symptoms and stabilized the metabolic state on long‐term follow‐up. Mutation analysis by polymerase chain reaction‐sequencing of the entire coding region of the HLCS gene revealed the c.1522C>T (p.R508W) mutation in six of the eight mutant alleles. This suggests it as the most common mutation in the Thai population, which paves the way for a rapid and unsophisticated diagnostic method for the ethnic Thai. Haplotype analysis revealed that the c.1522C>T was on three different haplotypes suggesting that it was recurrent, not caused by a founder effect. In addition, a novel mutation, c.1513G>C (p.G505R), was identified, expanding the mutational spectrum of this gene.     

Clinical findings and biochemical and molecular analysis of four patients with holocarboxylase synthetase deficiency

Holocarboxylase synthetase (HLCS) deficiency (HLCSD) is a rare autosomal recessive disorder of biotin metabolism. HLCS catalyzes the biotinylation of the four human biotin-dependent carboxylases. Using the newly available human genomic sequence, we report the map of HLCS genomic structure and the predicted exon/intron boundaries. Moreover, the molecular studies of four patients (two Italians, one Iranian, and one Australian) affected by HLCS deficiency are here reported. The clinical findings, the age of onset, and response to biotin treatment differed between our patients. The diagnosis was made by organic acid analysis and confirmed by enzymatic analysis in three patients. Six mutations in the HLCS gene were identified, including two novel (N511K and G582R) and four known missense mutations (L216R, R508W, V550M, and G581S). Five of the mutations are localized within the HLCS biotin-binding domain, whereas the L216R amino acid change is located in the N-terminal region outside of the putative biotin-binding domain. This mutation, previously reported in a heterozygous state, was detected for the first time in a patient with homozygous status. The patient's severe clinical phenotype and partial responsiveness to biotin support a genotype-phenotype correlation through the involvement of residues of the N-terminal region in a substrate specificity recognition or regulation of the HLCS enzyme.     

Reduced half-life of holocarboxylase synthetase from patients with severe multiple carboxylase deficiency

Multiple carboxylase deficiency is a clinical condition caused by defects in the enzymes involved in biotin metabolism, holocarboxylase synthetase (HLCS) or biotinidase. HLCS deficiency is a potentially fatal condition if left untreated, although the majority of patients respond to oral supplementation of 10-20 mg/day of biotin. Patients who display incomplete responsiveness to this therapy have a poor long-term prognosis. Here we investigated cell lines from two such HLCS-deficient patients homozygous for the c.647T>G p.L216R allele. Growth of the patients' fibroblasts was compromised compared with normal fibroblasts. Also the patient cells were not sensitive to biotin-depletion from the media, and growth rates could not be restored by re-administration of biotin. The molecular basis for the HLCS deficiency was further investigated by characterisation of the p.L216R protein. The HLCS mRNA was detected in MCD and normal cell lines. However, protein and enzyme activity could not be detected in the patients' cells. In vitro kinetic analysis revealed that enzyme activity was severely compromised for recombinantly expressed p.L216R and could not be increased by additional biotin. Furthermore, the turn-over rate for the mutant protein was double that of wildtype HLCS. These results help provide a molecular explanation for the incomplete biotin-responsiveness of this p.L216R form of HLCS.     

Mutations in the holocarboxylase synthetase gene HLCS

Holocarboxylase synthetase (HLCS) deficiency is an autosomal recessive disorder. HLCS is an enzyme that catalyzes biotin incorporation into carboxylases and histones. Since the first report of the cDNA sequence, 30 mutations in the HLCS gene have been reported. Mutations occur throughout the entire coding region except exons 6 and 10. The types of mutations are one single amino acid deletion, five single nucleotide insertions/deletions, 22 missense mutations, and two nonsense mutations. The only intronic mutation identified thus far is c.1519+5G>A (also designated IVS10+5G>A), which causes a splice error. Several lines of evidence suggest that c.1519+5G>A is a founder mutation in Scandinavian patients. Prevalence of this mutation is about 10 times higher in the Faroe Islands than in the rest of the world. The mutations p.L237P and c.780delG are predominant only in Japanese patients. These are probably founder mutations in this population. Mutations p.R508W and p.V550M are identified in several ethic groups and accompanied with various haplotypes, suggesting that these are recurrent mutations. There is a good relationship between clinical biotin responsiveness and the residual activity of HLCS. A combination of a null mutation and a point mutation that shows less than a few percent of the normal activity results in neonatal onset. Patients who have mutant HLCS with higher residual activity develop symptom after the neonatal period and show a good clinical response to biotin therapy.     

Clinical features,BTD gene mutations,and their functional studies of eight symptomatic patients with biotinidase deficiency from Southern China

Biotinidase (BTD) deficiency is a rare autosomal recessive metabolic disease, which develops neurological and cutaneous symptoms because of the impaired biotin recycling. Pathogenic mutations on BTD gene cause BTD deficiency. Clinical features and mutation analysis of Chinese children with BTD deficiency were rarely described. Herein, for the first time, we reported the clinical features, BTD gene mutations and their functional studies of eight symptomatic children with BTD deficiency from southern China. Fatigue, hypotonia, proximal muscular weakness, hearing deficits, rash and respiratory problems are common clinical phenotype of our patients. Seizures are observed only in patients with profound BTD deficiency. Five novel mutations were detected, among which c.637delC (H213TfsTer51) was found in 50% of our patients and might be considered as a common mutation. In vitro studies confirmed three mild mutations c.1368A>C (Q456H), c.1613G>A (R538H), and c.644T>A (L215H) which retained 10–30% of wild type enzyme activity, and six severe mutations c.235C>T (R79C), c.1271G>C (C424S), c.1412G>A (C471Y), c.637delC (H213TfsTer51), c.395T>G (M132W), c.464T>C (L155P), and c.1493dupT (L498FfsTer13) which retained <10% of wild type enzyme activity. c.1330G>C (D444H) decreased the protein expression but not activity of BTD enzyme, and H213TfsTer51 was structurally damaging while L498FfsTer13 was functionally damaging. These results will be helpful in establishing the definitive diagnosis of BTD deficiency at the gene level, offering appropriate genetic counseling, and providing clues to structure/function relationships of the enzyme.

     

A novel molecular mechanism to explain biotin-unresponsive holocarboxylase synthetase deficiency

Biotin (vitamins H and B7) is an important micronutrient as defects in its availability, metabolism or adsorption can cause serious illnesses, especially in the young. A key molecule in the biotin cycle is holocarboxylase synthetase (HLCS), which attaches biotin onto the biotin-dependent enzymes. Patients with congenital HLCS deficiency are prescribed oral biotin supplements that, in most cases, reverse the clinical symptoms. However, some patients respond poorly to biotin therapy and have an extremely poor long-term prognosis. Whilst a small number of mutations in the HLCS gene have been implicated, the molecular mechanisms that lead to the biotin-unresponsive phenotype are not understood. To improve our understanding of HLCS, limited proteolysis was performed together with yeast two-hybrid analysis. A structured domain within the N-terminal region that contained two missense mutations was identified in patients who were refractory to biotin therapy, namely p.L216R and p.L237P. Genetic studies demonstrated that the interaction between the enzyme and the protein substrate was disrupted by mutation. Further dissection of the binding mechanism using surface plasmon resonance demonstrated that the mutations reduced affinity for the substrate through a >15-fold increase in dissociation rate. Together, these data provide the first molecular explanation for HLCS-deficient patients that do not respond to biotin therapy.     

遗传性对称性色素异常症一家系ADAR基因突变研究

目的研究遗传性对称性色素异常症家系的RNA特异性的腺苷脱氨酶(RNA-specific adeno-sine deaminase,ADAR)基因的突变。方法收集一个遗传性对称性色素异常症家系的临床资料,采用聚合酶链反应及直接测序法对家系内成员进行ADAR基因突变位点检测,同时对50名无血缘关系健康对照者的该位点进行直接测序,并对国内外报道的ADAR基因突变进行总结。结果该家系中所有患者均存在ADAR基因c.2447G>A突变,导致p.R816K改变,而在家系内非患者及正常对照者中均未发现该突变。目前国内外已报道ADAR基因突变为64种。结论ADAR基因突变是中国人群中遗传性对称性色素异常的致病原因之一,ADAR基因各功能区域均可发生突变,但ADEAMc可能为其热点突变区域。     

A new insight into PMM2 mutations in the French population

Congenital disorder of Glycosylation type Ia is an autosomal recessive disorder, characterized by a central nervous system dysfunction and multiorgan failure associated with defective N-glycosylation and phosphomannomutase (PMM) deficiency related to mutations in the PMM2 gene (mRNA U85773.1, gene ID 5373). More than 75 different mutations have been previously described. In our study, 38 different mutations were found in 52 French families with CDG-Ia. Eleven mutations had not been previously published in CDG-Ia patients: eight missense and three splice mutations. We studied the PMM activity of eight novel recombinant mutant proteins in an E. coli expression system, comparing them with the wild type protein, c.422 G>A (R141H), and c.415 G>A (E139K) mutant proteins. We also studied the previously described c.590 C>A (E197A) found on the same allele as c.394 A>T (I132F). All mutant proteins studied except E197A had decreased activity and/or were thermolabile, and were pathogenic mutations. Haplotype studies revealed a founder effect for E139K mutation, only described in France and found in seven CDG-Ia families (7.6%). In contrast, at least two different haplotypes were observed for the R141H mutation in France, studied in 23 families. The R141H seems to be a combination of the "old" R141H mutation found all over Europe and a second "French" R141H, and could be substantially older than E139K.