Molecular characterization of familial hypercholesterolemia in German and Greek patients

We used the denaturing gradient gel electrophoresis (DGGE) method to define mutations in the promoter region, the 18 exons, and their flanking intronic sequences of the low-density lipoprotein (LDL) receptor gene LDLR, causing familial hypercholesterolemia (FH) phenotype in 100 German and in 100 Greek hypercholesterolemic individuals. In addition, we tested all patients for the presence of mutations in codons 3456-3553 of the gene encoding apolipoprotein B-100 (APOB). Twenty-six aberrant DGGE patterns were identified and subsequently directly sequenced. In LDLR, two novel missense mutations (c.1957G>T/p.V653F, c.647 G>A/p.C216Y) and one novel homozygous base substitution c.1-156 C>T in the repeat 2 of the promoter region were identified among German FH patients; one novel splice site c.1060+10C>G was identified among Greek FH patients. One of the German FH patients was a carrier for the mutations c.1171G>A/p.A391T and p.V653F, and two of the Greek FH patients were compound heterozygotes for the mutations c.1150C>T/p.Q384X and c.1158C>G/p.D386E. Two German FH patients carried the mutation p.R3500Q within APOB. Comparing the mutations within the LDLR gene of the two European FH populations, the German population seems to be more heterogeneous than the Greek cohort. Further studies in progress are trying to elucidate the responsiveness to drug therapy in association with LDLR genotype and the nutritional habits of the two FH populations.     

Novel sequence variants in the TMC1 gene in Pakistani families with autosomal recessive hearing impairment

Though many hearing impairment genes have been identified, only a few of these genes have been screened in population studies. For this study, 168 Pakistani families with autosomal recessive hearing impairment not due to mutations in the GJB2 (Cx26) gene underwent a genome scan. Two-point and multipoint parametric linkage analyses were carried out. Twelve families had two-point or multipoint LOD scores of 1.4 or greater within the transmembrane cochlear expressed gene 1 (TMC1) region and were subjected to further screening with direct DNA sequencing. Five novel putatively functional non-synonymous sequence variants, c.830A>G (p.Y277C), c.1114G>A (p.V372M), c.1334G>A (p.R445H), c.2004T>G (p.S668R), and c.2035G>A (p.E679K), were found to segregate within seven families, but were not observed in 234 Pakistani control chromosomes. The variants c.830A>G (p.Y277C), c.1114G>A (p.V372M), and c.1334G>A (p.R445H) occurred at highly conserved regions and were predicted to lie within hydrophobic transmembrane domains, while non-synonymous variants c.2004T>G (p.S668R) and c.2035G>A (p.E679K) occurred in extracellular regions that were not highly conserved. There is evidence that the c.2004T>G (p.S668R) variant may have occurred at a phosphorylation site. One family has the known splice site mutation c.536 -8T>A. The prevalence of non-syndromic hearing impairment due to TMC1 in this Pakistani population is 4.4% (95%CI: 1.9, 8.6%). The TMC1 protein might have an important function in K(+) channels of inner hair cells, which would be consistent with the hypothetical structure of protein domains in which sequence variants were identified.     

Functional analysis of 13 GBA mutant alleles identified in Gaucher disease patients: Pathogenic changes and "modifier" polymorphisms

Gaucher disease, the most prevalent sphingolipidosis, is caused by the deficient activity of acid beta-glucosidase, mainly due to mutations in the GBA gene. Over 200 mutations have been identified worldwide, more than 25 of which were in Spanish patients. In order to demonstrate causality for Gaucher disease, some of them: c.662C>T (p.P182L), c.680A>G (p.N188S), c.886C>T (p.R257X), c.1054T>C (p.Y313H), c.1093G>A (p.E326K), c.1289C>T (p.P391L), c.1292A>T (p.N392I), c.1322T>C (p.I402T), and the double mutants [c.680A>G; c.1093G>A] ([p.N188S; p.E326K]) and [c.1448T>C; c.1093G>A] ([p.L444P; p.E326K]), were expressed in Sf9 cells using a baculovirus expression system. Other well-established Gaucher disease mutations, namely c.1226A>G (p.N370S), c.1342G>C (p.D409H), and c.1448T>C (p.L444P), were also expressed for comparison. The levels of residual acid beta-glucosidase activity of the mutant enzymes produced by the cDNAs carrying alleles c.662C>T (p.P182L), c.886C>T (p.R257X), c.1054T>C (p.Y313H), c.1289C>T (p.P391L), and c.1292A>T (p.N392I) were negligible. The c.1226A>G (p.N370S), c.1322T>C (p.I402T), c.1342G>C (p.D409H), c.1448T>C (p.L444P), and [c.1448T>C; c.1093G>A] ([p.L444P; p.E326K]) alleles produced enzymes with levels ranging from 6 to 14% of the wild-type. The three remaining alleles, c.680A>G (p.N188S), c.1093G>A (p.E326K), and [c.680A>G; c.1093G>A] ([p.N188S; p.E326K]), showed higher activity (66.6, 42.7, and 23.2%, respectively). Expression studies revealed that the c.1093G>A (p.E326K) change, which was never found alone in a Gaucher disease-causing allele, when found in a double mutant such as [c.680A>G; c.1093G>A] ([p.N188S; p.E326K]) and [c.1448T>C; c.1093G>A] ([p.L444P; p.E326K]), decreases activity compared to the activity found for the other mutation alone. These results suggest that c.1093G>A (p.E326K) should be considered a "modifier variant" rather than a neutral polymorphism, as previously considered. Mutation c.680A>G (p.N188S), which produces a mutant enzyme with the highest level of activity, is probably a very mild mutation or another "modifier variant."     

Mutational analysis of mucopolysaccharidosis type VI patients undergoing a phase II trial of enzyme replacement therapy

Mucopolysaccharidosis type VI (MPS VI; Maroteaux-Lamy syndrome) is a lysosomal storage disorder caused by mutations in the N-acetylgalactosamine-4-sulfatase (ARSB) gene. These mutations result in a deficiency of ARSB activity. Ten MPS VI patients were involved in a phase II clinical study of enzyme replacement therapy. Direct sequencing of genomic DNA from these patients was used to identify ARSB mutations. Each individual exon of the ARSB gene was amplified by PCR and subsequently sequenced. Thirteen substitutions (c.215T>G [p.L72R] c.284G>A [p.R95Q], c.305G>A [p.R102H], c.323G>T [p.G108V], c.389C>T [p.P130L], c.511G>A [p.G171S], c.904G>A [p.G302R], c.944G>A [p.R315Q], c.1057T>C [p.W353R], c.1151G>A [p.S384N], c.1178A>C [p.H393P], c.1289A>G [p.H430R] and c.1336G>C [p.G446R]), one deletion (c.238delG), and two intronic mutations (c.1213+5G>A and c.1214-2A>G) were identified. Nine of the 16 mutations identified were novel (R102H, G108V, P130L, G171S, W353R, H430R, G446R, c.1213+5G>A and c.1214-2A>G). The two common polymorphisms c.1072G>A [p.V358M] and c.1126G>A [p.V376M] were identified in some of the patients, along with the silent mutations c.972A>G and c.1191A>G. Cultured fibroblast ARSB mutant protein and residual activity were determined for each patient and, together with genotype information, used to predict the expected clinical severity of each patient.     

Identification of seven novel mutations in ABCD1 by a DHPLC-based assay in Italian patients with X-linked adrenoleukodystrophy

We report the molecular findings in 14 patients (12 families) with X-linked adrenoleukodystrophy (X-ALD, MIM# 300100), a well-defined peroxisomal disorder attributed to mutations in the ABCD1 gene on chromosome Xq28. With the aims of determining the spectrum of mutations and developing an efficient molecular genetic test for analysis of at-risk women whose carrier status is unknown, and to offer molecular confirmation of their status to obligate heterozygotes, regardless of their clinical status, we carried out molecular screening by setting up a denaturing high-performance liquid chromatography (DHPLC)-based protocol. We identified eleven hemizygous base changes in ABCD1, including seven new mutations (c.145underscore;146ins4, c.264C>G, c.919C>T, c.994C>T, c.1027G>A, c.1508T>C, and c.1540A>C, resulting in the p.Pro193fs, p.Cys88Trp, p.Gln307X, p.Gln332X, p.Gly343Ser, p.Leu503Pro, and p.Ser514Arg changes, respectively). Adding new variants to the repertoire of ABCD1 mutations in X-ALD, our data provide an efficient, cost-effective, and reliable DHPLC detection protocol for mutation screening of X-ALD families.     

五个Dysferlinopathy家系的 DYSF基因变异分析

目的:对5个Dysferlinopathy家系进行 DYSF基因变异分析,明确其致病原因。 方法:应用高通量测序技术进行检测,确定可疑变异后应用Sanger测序进行变异位点验证,根据美国医学遗传学及基因组学学会(American College of Medical Genetics and Ge...     

Molecular analysis in glycogen storage disease 1 non-A: DHPLC detection of the highly prevalent exon 8 mutations of the G6PT1 gene in German patients

We investigated the molecular basis of glycogen storage disease type 1 non-A (GSD1 non-A) in 21patients. In addition to 8 novel mutations within the G6PT1 gene (c.250T>A, c.580G>A, c.627C>T, c.653-4delAG, c. 844C>A, c.1071A>C, c.1268G>A, c.1348G>A), we found a remarkably high prevalence of exon 8 mutations in German patients. The c.1211-2delCT mutation and the c.1184G>T mutation accounted for 32% and 29% of mutant chromosomes, respectively, supporting the hypothesis of a Middle European origin of these two mutations. Together with less common mutations, 79% of German GSD1 non-A patients were either homozygous or heterozygous for an exon 8 mutation. In addition to direct sequencing, these exon8 mutations could be detected by mutation-specific methods such as the detection of heteroduplex formation on polyacrylamide gel electrophoresis or by the amplification of DNA segments by allele-specific oligonucleotides. Furthermore, the use of denaturating high performance liquid chromatography (DHPLC) allowed a 100% detection and discrimination of all exon 8 mutations. In conclusion from these results, we recommend the use of either conventional or DHPLC screening as the initial non-invasive and efficient diagnostic procedure in patients with GSD1 non-A from populations with a similar distribution of mutations. Hum Mutat 16:177, 2000.     

CCM2 gene polymorphisms in Italian sporadic patients with cerebral cavernous malformation: a case-control study

Cerebral cavernous malformations (CCMs) are vascular lesions of the CNS characterized by abnormally enlarged capillary cavities that can occur sporadically or as a familial autosomal dominant condition with incomplete penetrance and variable clinical expression attributable to mutations in three different genes: CCM1 (Krit1), CCM2 (MGC4607) and CCM3 (PDCD10). Among our group of CCM Italian patients, we selected a cohort of sporadic cases negative for mutations in CCM genes. In this cohort, five variants in CCM2 gene were detected, which proved to be the known polymorphisms in intronic regions (IVS2-36A>G and IVS8 +119 C>T) and in coding sequence (c.157 G>A in exon 2, c.358 G>A in exon 4 and c.915 G>A in exon 8). Therefore, we undertook a case-control study to investigate the possible association of these polymorphisms with sporadic CCMs. The five polymorphisms were identified in 91 CCM sporadic patients and in 100 healthy controls by direct sequencing methods using lymphocyte DNA. Polymorphisms IVS2-36A>G and c.915 G>A showed statistically significant differences in frequencies between patients and controls [(χ2, 6.583; P<0.037); (χ2, 14.205; P<0.001)]. The prevalence of the wild-type genotype was significantly lower in the CCM group than in the control sample. Patients with the A/G and G/G genotypes (IVS2-36A>G) had a significant increase for CCM risk (OR, 3.08; 95% CI, 1.5-5.9 and OR, 4.3; 95% CI, 1.4-22.6) and the same was observed for the polymorphism c.915 G> A (genotype G/A OR, 6.1; 95% CI, 3.0-12.6 and genotype A/A OR, 2.79). In addition, the polymorphisms c.358 G>A in exon 4 (χ2, 15.977; P<0.04) and c.915 G>A in exon 8 (χ2, 18.109; P<0.02) were significantly associated with different types of symptoms. Haplotype analysis, performed only on polymorphisms c.358 G>A (p.Val120Ile), c.915 G>A (p.Thr305 Thr) and IVS2-36A>G, shows that haplotype GAG (+--) significantly increased among CCM sporadic patients compared to the control group. Significant differences between patients and controls were observed only for IVS2-36A>G and c.915 G>A polymorphisms indicating their possible association with sporadic CCMs and an increased risk of CCM. On the other hand, polymorphisms c.358 G>A and c.915 G>A were associated with a more benign course of the disease. These data were confirmed by the haplotype GAG (+--) frequencies.     

Germline mutations of the MSR1 gene in prostate cancer families from Germany

The MSR1 gene at 8p22 has been suggested as a candidate gene for hereditary prostate cancer because germline variants have been found to be associated with the disease. Aside from a single nonsense mutation (R293X) that was found repeatedly at low frequencies in several samples, little evidence has been gained by follow-up studies to confirm the gene's relevance for prostate cancer. Prompted by reasonable support for a linkage to 8p22, we sought to determine the mutation spectrum of MSR1 in our family sample. Screening of 139 probands (representing 139 prostate cancer families) revealed 15 novel and a total of 20 sequence variants within the 10 coding exons and their intronic proximities. Aside from the known mutation c.877C>T (R293X) present in two of our families, we identified a second nonsense allele (c.251C>G; S84X) and a splice-site mutation (c.818-1G>A) that results in mRNA instability (each in a single pedigree). The novel missense alleles were c.703C>T (H235Y), c.856C>T (P286S), c.905C>T (P302L), c.1193C>G (A398G), and c.1289A>G (K430R). Of the eight variants that affect the encoded protein (splice site, nonsense, and missense), only R293X as well as the polymorphism c.823C>G (P275A) were additionally present at remarkable frequencies in further samples of sporadic prostate cancer and controls. Of note, carriers of R293X were equally frequent in 367 sporadic prostate cancer cases (1.9%) and in 197 controls (2.0%). To our knowledge, our study is the first to demonstrate further loss of function variants of MSR1 apart from R293X. Nevertheless, the low frequencies of deleterious alleles, in addition to an apparently moderate penetrance, does not support MSR1 as a major susceptibility gene in this family sample.     

Novel RS1 mutations associated with X-linked juvenile retinoschisis

To identify mutations in the retinoschisin (RS1) gene in families with X-linked retinoschisis (XLRS). Twenty families with XLRS were enrolled in this study. All six coding exons and adjacent intronic regions of RS1 were amplified by polymerase chain reaction (PCR). The nucleotide sequences of the amplicons were determined by Sanger sequencing. Ten hemizygous mutations in RS1 were detected in patients from 14 of the 20 families. Four of the ten mutations were novel, including c:176G>A (p:Cys59Tyr) in exon?3, c:531T>G (p:Tyr177X), c:607C>G (p:Pro203Ala) and c:668G>A (p:Cys223Tyr) in exon?6. These four novel mutations were not present in 176 normal individuals. The remaining six were recurrent mutations, including c:214G>A (p:Glu72Lys), c:304C>T (p:Arg102Trp), c:436G>A (p:Glu146Lys), c:544C>T (p:Arg182Cys), c:599G>A (p:Arg200His) and c:644A>T (p:Glu215Val). Our study expanded the mutation spectrum of RS1 and enriches our understanding of the molecular basis of XLRS.     

Detection of alpha-galactosidase a mutations causing Fabry disease by denaturing high performance liquid chromatography

Mutations in the alpha-galactosidase A (alpha-Gal A, GLA) gene cause Fabry disease, an X-linked recessive lysosomal storage disease. The majority of mutations are private, and confirmation of carrier status in females requires the definitive identification of a DNA mutation. In addition, knowledge of a family's mutation enables rapid and precise preimplantation and prenatal genetic testing. Here we report the development and use of DHPLC to rapidly and cost-effectively screen for alpha-Gal A mutations. Optimal DHPLC partial denaturing conditions for mutation detection were established for each PCR amplicon corresponding to the seven alpha-Gal A exons and their adjacent intronic/flanking sequences. At least five known mutations in each exon (45 in total) were screened by DHPLC to validate the method. Mutation detection was then performed in 14 affected males diagnosed by enzyme assay and 39 at-risk females, and the amplicons with abnormal DHPLC profiles were sequenced. In all affected males, and in 32 of the 39 at-risk females, four and 16 previously reported and 10 and 15 new mutations were identified, respectively. Sequencing all seven alpha-Gal A gene amplicons in the seven at-risk females who had normal DHPLC profiles excluded them as mutation carriers. Only one mutation (p.P362L) was not initially identified by its DHPLC profile, but in retrospect the profile was abnormal, emphasizing the need for experience in inspecting the profiles. In addition, this technique detected two new intronic polymorphisms, c.640-16A>G and c.1000-22C>T, with frequencies of 0.14 and 0.25 in both normal individuals and Fabry patients, respectively. This DHPLC method should improve the rapidity and cost-effectiveness of alpha-Gal A mutation identification in affected males and carrier females for Fabry disease.     

Mutation analysis of the entire keratin 5 and 14 genes in patients with epidermolysis bullosa simplex and identification of novel mutations

Epidermolysis bullosa simplex is a group of blistering skin disorders caused by defects in one of the keratin genes, KRT5 and KRT14. Previously reported KRT5 and KRT14 mutations are clustered in several hotspots, namely the rod ends of the 1A and 2B domains and in the non-helical linker region L12. Therefore, genomic KRT5 and KRT14 mutation analysis was initially limited to these hotspots. In this study we describe the screening of nine EBS patients for mutations in the hotspots. In two patients, with the Koebner and the Weber-Cockayne subtypes of epidermolysis bullosa simplex respectively, we could, however, not identify any mutation in one of the hotspot domains of KRT5 and KRT14. Therefore, it appeared to be necessary to screen the entire genes for mutations. For KRT5, a complete genomic mutation detection system was previously described. We now developed a complete genomic mutation detection system for KRT14. For the amplification of the KRT14 genes, we make use of restriction sites to exempt the keratin 14 pseudogene sequence from polymerase chain reaction amplification. Using the complete genomic mutation detection system for both KRT5 and KRT14, we identified four novel KRT5 mutations (IVS1-1G>C, K404E, A438D, E475K), two of which are outside the KRT5 hotspot domains, and three novel KRT14 mutations (IVS4+1G>A, L408M, L130P).     

一例β-酮硫解酶缺乏症患儿 ACAT1基因变异分析

目的:探讨1例经新生儿疾病筛查拟诊为β-酮硫解酶缺乏症(β-ketothiolase deficiency,BKD)患儿的致病基因变异特点,明确其致病原因。方法:通过多重探针杂交富集患儿 ACAT1基因的全部编码区及其侧翼区序列进行高通量测序,确定可疑变异后应用Sanger测序进行变异位点验证。采用多种在线...     

七个鸟氨酸氨甲酰基转移酶缺陷症家系基因变异分析及产前诊断

目的对7个鸟氨酸氨甲酰基转移酶缺陷症(ornithine transcarbamylase deficiency,OTCD)家系进行OTC基因变异检测,明确其致病原因并为家系的遗传咨询和产前诊断提供依据。方法应用靶向高通量测序(next-generation sequencing,NGS)技术对7例经串联质谱筛查或临床诊断可疑OTCD的患儿或其母亲进行遗传代谢病相关基因panel检测,发现可疑致病变异位点后,应用PCR扩增和Sanger测序进行变异验证分析。在患儿母亲再次妊娠时抽取绒毛或羊水细胞进行相应基因变异检测,用于产前诊断。结果7个家系中共检测到7种OTC基因变异,分别为c.583G>A(p.Glyl95Arg).c.6260 T(p.Ala209Val)、c.6740 T(p.Pro225Leu)、c.482A>G(p.Asnl61Ser)、IVS1-2A>G、c.116G>T(p.Gly39Val).c.898delT(p.300Phefs*22),其中IVSl-2A>G、c・116G>T(p.Gly39Val)和c.898delT(p.300Phefs*22)为未报道过的新变异。产前诊断家系中3例胎儿基因测序均发现携带OTC基因变异半合子,性别为男性,孕妇选择终止妊娠,胎儿流产组织基因变异分析结果与产前诊断一致;另1例胎儿为OTC基因杂合变异,性别为女性,出生后新生儿筛查结果阴性,随访12个月,生长发育未见异常。结论OTC基因变异为7个OTCD家系的致病原因,致病变异的检出为家系的遗传咨询和产前诊断提供了依据。     

Identification of novel mutations in classical galactosemia

Classical galactosemia is an autosomal recessive disorder of galactose metabolism due to galactose-1-phosphate uridyltransferase (GALT) deficiency. Treatment through restriction of dietary galactose intake is lifesaving, but, in spite of this diet, most patients develop abnormalities. In this paper we report the mutational spectrum of classical galactosemia in a cohort of 123 Dutch patients, all with biochemically proven classical galactosemia. In the human GALT gene, which is located on chromosome 9p13, we identified 24 different mutations, including nine mutations that have not been reported previously. The novel mutations include five missense mutations (c.152G>A/p.R51Q, c.404C>T/p.S135W, c.687G>T/p.K229N, c.756G>T/p.Q252H, and c.1140A>C/p.X380C), a frame shift mutation (c.410dupT), a splice site mutation (c.821-2A>G), a possible branch point mutation (c.508-29delT), and a large deletion encompassing at least exons 1-11. Six of these novel mutations were found in patients of Dutch descent: p.R51Q, p.S135W, p.K229N, p.Q252H, p.X380C, and c.410dupT.     

Medium chain acyl-CoA dehydrogenase deficiency detected among Hispanics by New Jersey newborn screening

In the follow-up of New Jersey newborn screens suggestive of medium chain acyl-CoA dehydrogenase deficiency (MCADD) during a 30-month period, we identified five patients of Hispanic American ethnicity. With information provided by the New Jersey Department of Health and Human Services Newborn Screening program we calculated an overall cumulative incidence of approximately 7.20/100,000 for MCADD; 7.58/100,000 among Hispanic Americans and 7.08/100,000 among non-Hispanic Americans. Among the five Hispanic American infants who screened positive, a common variant (c.443G>A [p.R148K]) was identified which accounted for 30% of the alleles; c.799G>A (p.G267R) and c.985A>G (p.K329E) each accounted for an additional 20%; and a novel variant c.302G>A (p.G101E) was identified in one patient. Although treated prospectively during interim illnesses to prevent unwanted sequelae; till date, none of the patients carrying the c.443G>A variant have been symptomatic. ? 2012 Wiley Periodicals, Inc.     

Large-scale population-based metabolic phenotyping of thirteen genetic polymorphisms related to one-carbon metabolism

Several polymorphisms of genes involved in one-carbon metabolism have been identified. The reported metabolic phenotypes are often based on small studies providing inconsistent results. This large-scale study of 10,601 population-based samples was carried out to investigate the association between a panel of biochemical parameters and genetics variants related to one-carbon metabolism. Concentrations of total homocysteine (tHcy), folate, vitamin B(12) (cobalamin), methylmalonic acid (MMA), vitamin B(2) (riboflavin), vitamin B(6) (PLP), choline, betaine, dimethylglycine (DMG), cystathionine, cysteine, methionine, and creatinine were determined in serum/plasma. All subjects were genotyped for 13 common polymorphisms: methylenetetrahydrofolate reductase (MTHFR) c.665C>T (known as 677C>T; p.Ala222Val) and c.1286A>C (known as 1298A>C; p.Glu429Ala); methionine synthase (MTR) c.2756A>G (p.Asp919Gly); methionine synthase reductase (MTRR) c.66A>G (p.Ile22Met); methylenetetrahydrofolate dehydrogenase (MTHFD1) c.1958G>A (p.Arg653Gln); betaine homocysteine methyltransferase (BHMT) c.716G>A (known as 742G>A; p.Arg239Gln); cystathionine beta-synthase (CBS) c.844_845ins68 and c.699C>T (p.Tyr233Tyr); transcobalamin-II (TCN2) c.67A>G (p.Ile23Val) and c.776C>G (p.Pro259Arg); reduced folate carrier-1 (SLC19A1) c.80G>A (p.Arg27His); and paraoxonase-1 (PON1) c.163T>A (p.Leu55Met) and c.575A>G (p.Gln192Arg). The metabolic profile in terms of the measured vitamins and metabolites were investigated for these 13 polymorphisms. We confirmed the strong associations of MTHFR c.665C>T with tHcy and folate, but also observed significant (P<0.01) changes in metabolite concentrations according to other gene polymorphisms. These include MTHFR c.1286A>C (associations with tHcy, folate and betaine), MTR c.2756A>G (tHcy), BHMT c.716G>A (DMG), CBS c.844_845ins68 (tHcy, betaine), CBS c.699C>T (tHcy, betaine, cystathionine) and TCN2 c.776C>G (MMA). No associations were observed for the other polymorphisms investigated.     

Mutations in CYP1B1 cause primary congenital glaucoma by reduction of either activity or abundance of the enzyme

Primary congenital glaucoma (PCG) is an autosomal recessive disorder caused predominantly by mutations in the CYP1B1 gene. A total of five frequent single nucleotide polymorphisms (SNPs) have been identified in the coding sequence of CYP1B1: rs10012C>G (p.R48G), rs1056827G>T (p.A119S), rs1056836C>G (p.V432L), rs1056837C>T (p.D449D), and rs1800440A>G (p.N453S). We performed a functional characterization of four common CYP1B1 variants presenting different coding SNP haplotypes (RAVDN, GSLDN, RALDS, and RALDN) and five CYP1B1 mutations reported for PCG patients: c.182G>A (p.G61E), c.608A>G (p.N203S), c.1033_1035del (p.L343del), c.241 T>A (p.Y81N), and c.685G>A (p.E229 K). Each mutation was embedded in its corresponding background SNP haplotype. The common variants revealed variation in enzymatic activity; among them, RAVDN showed the highest activity. Mutants p.G61E, p.N203S, and p.L343del each revealed a residual activity (<10%) of their respective haplotype. The microsomal CYP1B1 abundance relative to total protein also showed variation in common variants and a significant reduction in p.L343del, p.Y81N, and p.E229 K. The free energy of folding (DeltaDeltaG) values suggest that the lower stability of the mutants is one key property leading to the experimentally observed lower protein abundance. Our new measure of relative enzymatic activity (U/mg total protein), which combines activity and abundance values, was significantly lower for all five mutations compared to the corresponding background haplotype. We classified p.Y81N and p.E229 K not as mutations but as hypomorphic alleles, since their relative activity values are intermediate between bona fide mutations and the common variant with the lowest activity (RALDS). We propose that CYP1B1 mutations can act by either reducing enzymatic activity (p.G61E and p.N203S), reducing the abundance of the enzyme (p.Y81N and p.E229 K), or both (p.L343del).