中国汉族人群供-受者HLA-A、B、Cw、DRB1和DQB1高分辨等位基因频率分布及错配比例的研究

目的 从基因高分辨水平,分析中国汉族人群供-受者人类白细胞抗原(human leukocyte antigens,HLA)-A、B、Cw、DRB1、DQB1各位点等位基因频率和分布的多态性;及供-受者等位基因匹配情况.方法 采用基因测序分型(sequence based typing,SBT)、序列特异性寡核苷酸探针法(sequence specific oligonueleotide probe,SSOP)和序列特异性引物法(sequence specific primer,SSP),对2540名中国汉族人的(其中1168名受者,1372名供者)DNA标本进行HLA高分辨基因分型,并作统计学处理.结果 2540份样本中共检测到44种HLA-A等位基因,频率高于0.05的A*1101、A*2402、A*0201、A*0207、A*3303、A*0206、A*3001共占80.4%;81种HLA-B等位基因,频率高于0.05的B*4001、B*4601、B*5801、B*1302、B*5101共占43.0%;44种HLA-Cw等位基因,频率高于0.05的Cw*0702、Cw*0102、Cw*0304、Cw*0801、Cw*0602、Cw*0303、Cw*0302、Cw*0401共占80.3%;61种HLA-DRB1等位基因,频率高于0.05的DRB1*0901、DRB1*1501、DRB1*1202、DRB1*0803、DRB1*0701、DRB1*0405、DRB1*0301、DRB1*1101共占70.1%;22种HLA-DQB1等位基因,频率高于0.05的DQB1*0301、DQB1*0303、DQB1*0601、DQB1*0602、DQB1*0202、DQB1*0302、DQB1*0401、DQB1*0502、DQB1*0201共占87.4%.这5个位点均处于杂合子缺失状态,其中A、B、DRB1位点符合HardyWeinberg平衡(Hardy-Weinberg equi1ibrium,HWE)(P＞0.05);Cw、DQB1位点偏离HWE(P＜0.05);排除个别基因型观察值与期望值偏差较大外,这5个位点均符合HWE.在供-受者数据的比较中,HLA全相合(10/10)的比例仅22.4%;单个等位基因错配(9/10)的比例为24.6%;两个等位基因错配(8/10)的比例为26.3%.结论 中国汉族人群高分辨水平HLA-A、B、Cw、DRB1,DQB1等位基因频率及分布特点,对非亲缘造血干细胞移植供者检索有重要参考价值;并为中华骨髓库数据入库和利用提供遗传学依据.

Abstract：

Objective To analyze the allele frequencies and polymorphism of human leukocyte antigens (HLA) -A, B, Cw, DRB1 and DQB1 between donors-recipients on high-resolution typing; and to analyze the matching and mismatching proportion between donors and recipients. Methods HLA highresolution types were determined by sequence based typing (SBT), sequence specific oligonucleotide probe (SSOP) and sequence specific primer (SSP) on 2540 unrelated Chinese Han individuals including 1168 recipients and 1372 donors, then statistical analyses were carried out. Results Forty-four HLA-A alleles were detected, and among them the frequencies of A * 1101, A * 2402, A * 0201, A * 0207, A * 3303, A *0206 and A * 3001 exceeded 0.05, and accounted for 80.4%. Eighty-one HLA-B alleles were detected, and frequencies of B * 4001, B * 4601, B * 5801, B * 1302 and B * 5101 exceeded 0. 05, and accounted for 43. 0% of total. There were 44 HLA- Cw alleles, among them the frequencies of Cw * 0702, Cw * 0102,Cw * 0304, Cw * 0801, Cw * 0602, Cw * 0303, Cw * 0302 and Cw * 0401 exceeded 0.05, and were 80.3 %of total. There were 61 HLA-DRB1 alleles, the frequencies of DRB1 * 0901, DRB1 * 1501, DRB1 * 1202,DRB1 * 0803, DRB1 * 0701, DRB1 * 0405, DRB1 * 0301 and DRB1 * 1101 exceeded 0. 05, and were 70. 1% of total. Finally, 22 HLA-DQB1 alleles were detected, the frequencies of DQB1 * 0301, DQB1 *0303, DQB1 * 0601, DQB1 * 0602, DQB1 * 0202, DQB1 * 0302, DQB1 * 0401, DQB1 * 0502 and DQB1 *0201 exceeded 0. 05, and they were 87.4% of total. All the five loci were of heterozygote deficiency. The HLA-A, B and DRB1 loci conformed to Hardy-Weinberg equilibrium (HWE) (P＞0. 05); but HLA-Cw and HLA-DQB1 loci did not (P＜0.05). Except several particular genotypes, all the five loci conformed to HWE. After comparing data between donors and recipients, only 22.4% of recipients found HLA matched donors (10/10); 24. 6% of recipients found single HLA allele mismatched donors (9/10); 26. 3% of recipients had two HLA alleles mismatched donors (8/10). Conclusion The characteristics of allele frequencies and polymorphism of HLA-A, B, Cw, DRB1 and DQB1 on high-resolution typing in Chinese Han population is valuable for donor searching in unrelated hematopoietic stem cell transplantation, and it provides genetic basis for donor registry and usage of donor resource for Chinese Marrow Donor Program.     

A novel HLA-C allele, Cw*0119, isolated from the Han Chinese

A novel HLA-C allele, Cw*0119, which was identified from an individual of the Han Chinese, differs from Cw*010201 at codon 76 (AGC-->TGC) and codon 178 (CTG-->CCG).     

Study on the polymorphisms of HLA‐ABCDQB1DRB1 alleles and haplotypes in Hubei Han population of China

The present study aimed to analyse the frequencies of human leukocyte antigen HLA‐ABCDQB1 and HLA‐DRB1 alleles and haplotypes in a subset of 3,732 Han population from Hubei of China. All samples were typed in the HLA‐ABCDQB1 and HLA‐DRB1 loci using the sequence‐based typing method; subsequently, the HLA polymorphisms were analysed. A total of 47 HLA‐A, 89 HLA‐B, 43 HLA‐C, 49 HLA‐DRB1 and 24 HLA‐DQB1 alleles were identified in the Hubei Han population. The top three most frequent alleles in the HLA‐ABCDQB1 and HLA‐DRB1 were A*11:01 (0.2617), A*24:02 (0.1590), A*02:07 (0.1281); B*46:01 (0.1502), B*40:01 (0.1409) and B*58:01 (0.0616); C*01:02 (0.2023), C*07:02 (0.1691) and C*03:04 (0.1175); and DQB1*03:01 (0.2000), DQB1*03:03 (0.1900), DQB1*06:01 (0.1187); DRB1*09:01 (0.1790), DRB1*15:01 (0.1062) and DRB1*12:02 (0.0841), respectively. Meanwhile, the three most frequent two‐loci haplotypes were A*02:07‐C*01:02 (0.0929), B*46:01‐C*01:02 (0.1366) and DQB1*03:03‐DRB1*09:01 (0.1766). The three most frequent three‐loci haplotypes were A*02:07‐B*46:01‐C*01:02 (0.0883), B*46:01‐DQB1*03:03‐DRB1*09:01 (0.0808) and C*01:02‐DQB1*03:03‐DRB1*09:01 (0.0837). The three most frequent four‐loci haplotypes were A*02:07‐B*46:01‐C*01:02‐DQB1*03:03 (0.0494), B*46:01‐DRB1*09:01‐C*01:02‐DQB1*03:03 (0.0729) and A*02:07‐B*46:01‐DQB1*03:03‐DRB1*09:01 (0.0501). The most frequent five‐loci haplotype was A*02:07‐B*46:01‐C*01:02‐DQB1*03:03‐DRB1*09:01 (0.0487). Heat maps and multiple correspondence analysis based on the frequencies of HLA specificity indicated that the Hubei Han population might be described into Southern Chinese populations. Our results lay a certain foundation for future population studies, disease association studies and donor recruitment strategies.     

Allelic and haplotype diversity of HLA‐A,HLA‐B and HLA‐DRB1 gene at high resolution in the Nanning Han population

The distribution of human leucocyte antigen (HLA) allele and haplotype varied among different ethnic populations. In this study, we investigated the allele and haplotype frequencies of HLA‐A, HLA‐B and HLA‐DRB1 loci in the Nanning Han population who live in Guangxi province of China. We identified 26 HLA‐A, 56 HLA‐B and 31 HLA‐DRB1 alleles in 562 Nanning individuals of Han ethnic group by sequence‐based typing method. Of these, the three most common alleles in HLA‐A, HLA‐B and HLA‐DRB1 loci, respectively, were A*11:01 (32.12%), A*02:07 (12.54%), A*24:02 (12.01%); B*46:01 (14.41%), B*15:02 (13.61%), B*40:01 (11.48%); DRB1*15:01 (14.15%), DRB1*16:02 (11.57%) and DRB1*12:02 (10.14%). With the exception of HLA‐DRB1, the p values of the HLA‐A and HLA‐B loci showed that the HLA allelic distribution in this population was in accordance with Hardy–Weinberg expectation (p > 0.05). A total of 173 HLA~A‐B~DRB1 haplotype with a frequency of >0.1% were presented and the three most common haplotype were HLA‐A*33:03~B*58:01~DRB1*03:01 (6.12%), HLA‐A*11:01~B*15:02~DRB1*12:02 (3.39%) and HLA‐A*11:01~B*15:02~DRB1*15:01 (3.22%). The phylogenetic tree and the principal component analysis suggested that Nanning Han population had a relative close genetic relationship with Chinese Zhuang population and a relative distant genetic relationship with Northern Han Chinese. The information will be useful for anthropological studies, for HLA matching in transplantation and disease association studies in the Chinese population.     

A novel HLA-DRB1 allele, DRB1*112802, was identified in a Chinese individual

We report here a novel human leukocyte antigen-DRB1 allele, DRB1*112802, which was identified from a Chinese individual during sequence-based typing. The new allele is identical to DRB1*112801 except for one nucleotide change at nucleotide 189 (A → G ), codon 34 Q (CAA) → Q (CAG), no coding change.     

Utility of next‐generation sequencing methods to identify the novel HLA alleles in potential stem cell donors from Chinese Marrow Donor Program

The human leucocyte antigen (HLA) is the most polymorphic region of the human genome. Compared with Sanger‐sequencing‐based typing (SBT) methods, next‐generation sequencing (NGS) has significantly higher throughput and depth sequencing characteristics, having dramatic impacts on HLA typing in clinical settings. Here, we performed NGS technology with Ion Torrent S5 platform to evaluate the potential four novel HLA alleles detected in five donors from Chinese Marrow Donor Program (CMDP, Shaanxi Province) during routine Sanger SBT testing. We also predicted the highest estimated relative frequency novel allele‐bearing haplotypes according to their phenotypes and HaploStats database. NGS assays, as it provided the phase‐defined and complete sequencing information, undoubtedly increase novel allele identification which will greatly enrich HLA database and provide more information for donor selection.     

广州4194份脐带血HLA-A、B、DRB1等位基因型和单倍型频率研究

目的 对广州脐血库10年来保存的脐血人类白细胞抗原(human leukocyte antigen,HLA)等位基因及单倍型分布特征进行分析.方法 采用单克隆板,序列特异引物聚合酶链反应,PCR序列特异性寡核苷酸探针和DNA测序分型方法对广州脐血库内4194份脐带血进行HIA-A、B、DRB1等位基因分型.用Arlequm软件计算HLA基因频率和单倍型频率.结果 在广州脐血库中,HLA-A、B、DRB1等位基因型分别有18,43,13种.累积频率>50%的显著高频率等位基因是:A*11,A*02,A*24,A*33,B*40,B*15,B*46,B*13,DRB1*12,DRB1*15,DRB1*09,DRB1*04;最常见的单倍型为:A2-B46、B6-DR9、A11-DR12、A2-B6-DR9.结论 广州脐血库脐血捐献者HIA-A、B、DRB1等位基因型及单倍型分布具有典型南方人群的特点,此资料有助于为临床移植寻找合适匹配的供受对.     

Class II HLA allele polymorphism: DRB1, DQB1 and DPB1 alleles and haplotypes in the New Zealand Maori population

Class II alleles of interest to transplantation comprise the DRB1, DQB1 and DPB1 loci. Sequence-based typing was used to determine the class II allelic variability present in New Zealand Maori, a population with close genetic ties to Polynesia and known anthropological and linguistic connections to mainland Asia. The most common DRB1 alleles identified were DRB1*1201, DRB1*110101, DRB1*0403 and DRB1*080302, with frequencies of 21.5%, 14%, 11.25% and 9.25%, respectively. Standard linkages between the DRB1 locus and the DRB3, 4 and 5 loci were maintained, with no novel patterns identified. The most common DQB1 alleles identified were DQB1*030101, DQB1*060101, DQB1*020101, DQB1*0602 and DQB1*050201, with frequencies of 29.5%, 8%, 7.8%, 6.4% and 6.2%, respectively. The most common DPB1 alleles identified were DPB1*0501, DPB1*040101 and DPB1*020102, with frequencies of 40.2%, 28.89% and 15.83%, respectively. A total of 80 estimated DRB1-DQB1 two-locus haplotypes were detected. DRB1*1201-DQB1*030101 was the most frequent (15.40%) haplotype, followed by DRB1*110101-DQB1*030101 (9.97%), DRB1*0403-DQB1*030201 (7.37%) and DRB1*080302-DQB1*060101 (5.96%). The allelic variation determined is being used in further analysis of the requirement for bone marrow transplantation in the New Zealand Maori population and has implications for optimal ethnic donor distribution on the New Zealand Bone Marrow Donor Registry, anthropological studies and disease association.     

河南地区汉族人群复发性流产患者HLA-DRB1、DQB1等位基因多态性的研究

目的探讨复发性流产易感性与人类白细胞抗原(HLA)DR、DQ区域基因多态性的关系。方法采用序列特异性引物聚合酶链反应(PCR-SSP),分析200例复发性流产患者(患者组)和200例无不良妊娠史正常妇女(对照组)的DRB1和DQB1基因型。结果患者组中的DQB1*03(39.25%)等位基因频率显著高于对照组(32.5%)(P=0.047<0.05,RR=1.208),DQB1*05(14%)等位基因频率较对照组显著降低(22.75%)(P=0.001<0.05,RR=0.615);患者组中DRB1*09(14%)等位基因频率显著高于对照组(9.25%)(P=0.036<0.05,RR=1.514),DRB1*12(8.5%)等位基因频率较对照组显著降低(14%)(P=0.014<0.05,RR=0.607)。结论河南地区汉族人群中DQB1*03、DRB1*09可能是复发性流产的易感基因,而DQB1*05、DRB1*12可能对复发性流产的发生有保护作用。     

A novel HLA-B*15 allele, B*9534, identified by sequence-based typing in the Chinese population

We report here the identification of a novel human leukocyte antigen-B*9534 allele that was detected by polymerase chain reaction sequence-based typing.     

Identification of a novel HLA-DRB1*12 allele, DRB1*1218, in Chinese population

Here, we report the identification of a novel human leukocyte antigen-DRB1*12 variant, DRB1*1218 allele, in a Chinese Han individual. The novel DRB1*12 variant allele differed from the closest allele DRB1*120201 by nucleotide 262 G>C (codon 59 GAG>CAG) missense mutation in exon 2, which resulted in an amino acid substitution of Glu>Gln.     

HLA‐A, ‐B and ‐DRB1 allele and haplotype frequencies of 8333 Chinese Han from the Zhejiang province,China

The distribution of human leucocyte antigen (HLA) allele and haplotype is varied among different ethnic populations. In this study, HLA‐A, ‐B and ‐DRB1 allele and haplotype frequencies were determined in 8333 volunteer bone marrow donors of Zhejiang Han population using the polymerase chain reaction sequence‐based typing. A total of 52 HLA‐A, 96 HLA‐B and 61 HLA‐DRB1 alleles were found. Of these, the top three frequent alleles in HLA‐A, HLA‐B and HLA‐DRB1 loci, respectively, were A*11:01 (24.53%), A*24:02 (17.35%), A*02:01 (11.58%); B*40:01 (15.67%), B*46:01 (11.87%), B*58:01 (9.05%); DRB1*09:01 (17.54%),DRB1*12:02 (9.64%) and DRB1*08:03 (8.65%). A total of 171 A‐B‐DRB1 haplotypes with a frequency of >0.1% were presented and the five most common haplotypes were A*33:03‐B*58:01‐ DRB1*03:01, A*02:07‐B*46:01‐DRB1*09:01, A*30:01‐B*13:02‐DRB1*07:01, A*33:03‐B*58:01‐RB1*13:02 and A*11:01‐B*15:02‐DRB1*12:02. The information will be useful for selecting unrelated bone marrow donors and for anthropology studies and pharmacogenomics analysis.     

Identification of a novel HLA-B*15 allele, B*9529, in the Chinese population

We report here the identification of a novel human leukocyte antigen-B*9529 allele that was detected by polymerase chain reaction sequence-based typing.     

辽宁汉族人群HLA-B等位基因多态性的分布

目的调查辽宁汉族人群HLA-B等位基因的遗传多态性。方法用聚合酶链反应．序列特异性引物方法对辽宁8962名健康无关汉族人进行HLA-B等位基因分型，计算HLA-B等位基因频率并与不同人群HLA-B等位基因的多态性进行比较。结果共检出HLA-B等位基因34种，其中B＊15（14．42％）、B＊40（14．33％）和B＊13（11．99％）基因频率分布较高，B＊82、B＊83等位基因未检出；HLA-B座位特异性49种。该人群与南北方汉族人群、日本人、黑人和白人分别进行X^2检验差异有统计学意义，X^2值分别为1584．799、72．145、1393．339、7406．288和5311．947。结论辽宁汉族人群HLA-B基因多态性分布有其自身特点，它的遗传特征不同于既往的南、北方汉族。     

A novel HLA-B*37 allele, B*370105, was identified in a Chinese Han individual

We report here the sequence of a novel human leukocyte antigen B*37 allele, B*370105, which is identical to B*370101 except for a single nucleotide substitution in exon 3 at nucleotide 558 where C>A, codon 162 GGC>GGA, no coding change.     

HLA class I (A, B, C) and class II (DRB1, DQA1, DQB1, DPB1) alleles and haplotypes in the Han from southern China

In this study, polymerase chain reaction-sequence-specific oligonucleotide prode (SSOP) typing results for the human leukocyte antigen (HLA) class I (A, B, and C) and class II (DRB1, DQA1, DQB1, and DPB1) loci in 264 individuals of the Han ethnic group from the Canton region of southern China are presented. The data are examined at the allele, genotype, and haplotype level. Common alleles at each of the loci are in keeping with those observed in similar populations, while the high-resolution typing methods used give additional details about allele frequency distributions not shown in previous studies. Twenty distinct alleles are seen at HLA-A in this population. The locus is dominated by the A*1101 allele, which is found here at a frequency of 0.266. The next three most common alleles, A*2402, A*3303, and A*0203, are each seen at frequencies of greater than 10%, and together, these four alleles account for roughly two-thirds of the total for HLA-A in this population. Fifty alleles are observed for HLA-B, 21 of which are singleton copies. The most common HLA-B alleles are B*4001 (f= 0.144), B*4601 (f= 0.119), B*5801 (f= 0.089), B*1301 (f= 0.068), B*1502 (f= 0.073), and B*3802 (f= 0.070). At the HLA-C locus, there are a total of 20 alleles. Four alleles (Cw*0702, Cw*0102, Cw*0801, and Cw*0304) are found at frequencies of greater than 10%, and together, these alleles comprise over 60% of the total. Overall, the class II loci are somewhat less diverse than class I. Twenty-eight distinct alleles are seen at DRB1, and the most common three, DRB1*0901, *1202, and *1501, are each seen at frequencies of greater than 10%. The DR4 lineage also shows extensive expansion in this population, with seven subtypes, representing one quarter of the diversity at this locus. Eight alleles are observed at DQA1; DQA1*0301 and 0102 are the most common alleles, with frequencies over 20%. The DQB1 locus is dominated by four alleles of the 03 lineage, which make up nearly half of the total. The two most common DQB1 alleles in this population are DQB1*0301 (f= 0.242) and DQB1*0303 (f= 0.15). Eighteen alleles are observed at DPB1; DPB1*0501 is the most common allele, with a frequency of 37%. The class I allele frequency distributions, expressed in terms of Watterson's (homozygosity) F-statistic, are all within expectations under neutrality, while there is evidence for balancing selection at DRB1, DQA1, and DQB1. Departures from Hardy-Weinberg expectations are observed for HLA-C and DRB1 in this population. Strong individual haplotypic associations are seen for all pairs of loci, and many of these occur at frequencies greater than 5%. In the class I region, several examples of HLA-B and -C loci in complete or near complete linkage disequilibrium (LD) are present, and the two most common, B*4601-Cw*0102 and B*5801-Cw*0302 account for more than 20% of the B-C haplotypes. Similarly, at class II, nearly all of the most common DR-DQ haplotypes are in nearly complete LD. The most common DRB1-DQB1 haplotypes are DRB1*0901-DQB1*0303 (f= 0.144) and DRB1*1202-DQB1*0301 (f= 0.131). The most common four locus class I and class II combined haplotypes are A*3303-B*5801-DRB1*0301-DPB1*0401 (f= 0.028) and A*0207-B*4601-DRB1*0901-DPB1*0501 (f= 0.026). The presentation of complete DNA typing for the class I loci and haplotype analysis in a large sample such as this can provide insights into the population history of the region and give useful data for HLA matching in transplantation and disease association studies in the Chinese population.     

HLA‐A,HLA‐B,HLA‐DRB1 allele and haplotype frequencies of 14 529 Chinese Han bone marrow donors living in Dalian,China

We investigated the allele and haplotype frequencies of HLA‐A, HLA‐B and HLA‐DRB1 loci in Dalian Chinese Han population using blood samples of unrelated marrow donors who live in Dalian. The genetic relationship between Dalian and different regions worldwide was further explored based on HLA status of different populations. A total of 14 529 samples were genotyped at 2‐digit level only by sequence‐specific oligonucleotide and sequence‐based typing methods. Allele frequencies of HLA‐A, HLA‐B and HLA‐DRB1 were calculated by the direct counting method. Haplotype frequencies and linkage disequilibrium (LD) values were calculated by the maximum likelihood method. F_ST values were calculated by allele frequency data of each locus. Phylogeny tree of Nei's D_A genetic distances was constructed by the UPGMA method. HLA‐A*02 was the most frequent allele at HLA‐A locus followed by A*11 and A*24. Alleles at HLA‐B locus ranked in decreasing order by frequency were B*40, B*15 and B*13. The three highest frequency alleles were DRB1*15, DRB1*09 and DRB1*12 at HLA‐DRB1 locus. A*30‐B*13‐DRB1*07 was the most frequent three‐locus haplotype. For the population relationships, Dalian had a relative close genetic relationship with Liaoning and Yantai‐Weihai and a relative distant genetic relationship with Australia. The information obtained in this study may provide useful information for anthropological studies, for disease‐association studies and helping bone marrow transplantation patients to search HLA‐matched donors.     

A novel HLA-DRB1 allele, DRB*1611, is identified in two Taiwanese individuals

Human leukocyte antigen (HLA)-DRB1*1611 has one nucleotide change at codon 14 (GAG→AAG) from DRB1*160201, resulting in a coding change from Glu to Lys.     

HLA‐A,HLA‐B and HLA‐DRB1 allele and haplotype diversity among volunteer bone marrow donors from Croatia

The determination of human leucocyte antigen (HLA)‐A, HLA‐B and HLA‐DRB1 alleles in the routine procedure of a volunteer hematopoietic stem cell (HSC) donor's registration in the Croatian Bone Marrow Donor Registry (CBMDR) is performed to enhance the odds of finding a suitable HLA compatible donor for patients in need of a HSC transplantation worldwide. However, besides its original purpose, it also provides valuable information about the HLA polymorphism among Croats. The aim of the present study was to analyse the HLA allele and haplotype frequencies in a sample of 4000 donors from CBMDR. The distribution of HLA‐A, HLA‐B and HLA‐DRB1 alleles did not demonstrate significant differences from the data reported for other European populations. The higher frequency of B*40:02 allele in comparison with B*40:01 and DRB1*11:04 in comparison with DRB1*11:01 is interesting because it represents a difference in comparison with the Western and Northern European populations which are a main source of donors for Croatian patients. The haplotype frequencies show a greater variation and difference in comparison with data from other registries and populations; however, due to a lack of high‐resolution haplotype data, comparison was possible only with a very limited number of other populations.     

A novel HLA-DRB1 allele, DRB1*1219, was identified by sequence-based typing in a Chinese leukaemia family

A novel human leukocyte antigen DRB1 allele, DRB1*1219, has been identified in a Chinese leukaemia patient and his family by polymerase chain reaction sequence-based typing, which has one nucleotide change at position 341 (C→T) in exon 2 from the closest matching allele DRB1*120201, resulting in an amino acid substitution from Ala→Val at codon 85.