Founder effects facilitate the use of a genotyping-based approach to molecular diagnosis in Swedish patients with familial hypercholesterolaemia.

AIM: To investigate whether genotyping could be used as a cost-effective screening step, preceding next-generation sequencing (NGS), in molecular diagnosis of familial hypercholesterolaemia (FH) in Swedish patients. METHODS AND RESULTS: Three hundred patients of Swedish origin with clinical suspicion of heterozygous FH were analysed using a specific array genotyping panel embedding 112 FH-causing mutations in the LDLR, APOB and PCSK9 genes. The mutations had been selected from previous reports on FH patients in Scandinavia and Finland. Mutation-negative cases were further analysed by NGS. In 181 patients with probable or definite FH using the Dutch lipid clinics network (DLCN) criteria (score ≥ 6), a causative mutation was identified in 116 (64%). Of these, 94 (81%) were detected by genotyping. Ten mutations accounted for more than 50% of the positive cases, with APOB c.10580G>A being the most common. Mutations in LDLR predominated, with (c.2311+1_2312-1)(2514)del (FH Helsinki) and c.259T>G having the highest frequency. Two novel LDLR mutations were identified. In patients with DLCN score < 6, mutation detection rate was significantly higher at younger age. CONCLUSION: A limited number of mutations explain a major fraction of FH cases in Sweden. Combination of selective genotyping and NGS facilitates the clinical challenge of cost-effective genetic screening in suspected FH. The frequency of APOB c.10580G>A was higher than previously reported in Sweden. The lack of demonstrable mutations in the LDLR, APOB and PCSK9 genes in ~1/3 of patients with probable FH strongly suggests that additional genetic mechanisms are to be found in phenotypic FH.

Genetic testing for familial hypercholesterolemia among survivors of acute coronary syndrome.

BACKGROUND: Familial hypercholesterolemia could be prevalent among patients with acute coronary syndrome. OBJECTIVE: To investigate both the frequency of causative mutations for familial hypercholesterolemia (FH) and the optimal selection of patients for genetic testing among patients with an acute coronary syndrome (ACS). METHODS: One hundred and sixteen patients with an ACS during 2009-2015 were identified through the SWEDEHEART registry. Patients who had either a high total cholesterol level ≥7 mmol L-1 combined with a triglyceride level ≤2.6 mmol L-1 , or were treated with lipid-lowering medication and had a total cholesterol level >4.9 mmol L-1 and a triglyceride level ≤2.6 mmol L-1 were included. Genetic testing was performed first with a regionally designed FH mutation panel (118 mutations), followed by testing with a commercially available FH genetic analysis (Progenika Biopharma). RESULTS: A total of 6.9% (8/116) patients had a FH-causative mutation, all in the LDL-receptor. Five patients were detected on the panel, and further testing of the remaining 111 patients detected an additional 3 FH-causative mutations. Baseline characteristics were similar in FH-positive and FH-negative patients with respect to age, gender, prior ACS and diabetes. Patients with a FH-causative mutation had higher Dutch Lipid Clinical Network (DLCN) score (5.5 (5.0-6.5) vs 3.0 (2.0-5.0), P < 0.001) and a higher low-density lipoprotein level (5.7 (4.7-6.5) vs 4.9 (3.5-5.4), P = 0.030). The Dutch Lipid Clinical Network (DLCN) score had a good discrimination with an area under the curve of 0.856 (95% CI 0.763-0.949). CONCLUSION: Genetic testing for FH should be considered in patients with ACS and high DLCN score.

Two genes encoding immune-regulatory molecules (LAG3 and IL7R) confer susceptibility to multiple sclerosis.

Multiple sclerosis (MS) is a T-cell-mediated disease of the central nervous system, characterized by damage to myelin and axons, resulting in progressive neurological disability. Genes may influence susceptibility to MS, but results of association studies are inconsistent, aside from the identification of HLA class II haplotypes. Whole-genome linkage screens in MS have both confirmed the importance of the HLA region and uncovered non-HLA loci that may harbor susceptibility genes. In this two-stage analysis, we determined genotypes, in up to 672 MS patients and 672 controls, for 123 single-nucleotide polymorphisms (SNPs) in 66 genes. Genes were chosen based on their chromosomal positions or biological functions. In stage one, 22 genes contained at least one SNP for which the carriage rate for one allele differed significantly (P<0.08) between patients and controls. After additional genotyping in stage two, two genes--each containing at least three significantly (P<0.05) associated SNPs--conferred susceptibility to MS: LAG3 on chromosome 12p13, and IL7R on 5p13. LAG3 inhibits activated T cells, while IL7R is necessary for the maturation of T and B cells. These results imply that germline allelic variation in genes involved in immune homeostasis--and, by extension, derangement of immune homeostasis--influence the risk of MS.

A NOTCH4 association with multiple sclerosis is secondary to HLA-DR*1501.

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) with supposedly autoimmune features known to be associated with a specific HLA DR-DQ haplotype (DR15, DQ6, or HLDRB1*1501,DRB5*0101,DQA1*0102,DQB1*0602). We have previously reported that the associated haplotype extends to HLA-B and described an independent association with HLA-A alleles in MS. Owing to a complex situation with extensive linkage disequilibria, it is still unclear whether classical HLA genes are responsible or whether associations may be due to other genes in this region. Here, we analyzed an association in MS with the NOTCH4 and TNFalpha (tumor necrosis factor-alpha) genes, located between the HLA-DRB1 gene and the HLA-A gene. For NOTCH4, located 0.4 Mb telomeric to HLA-DRB1, an SNP at position -25 and a trinucleotide repeat were investigated in 181 MS patients, and 180 controls also typed P = 0.027 for HLA-DRB and HLA-A. A modest association was observed (OR = 3.44) with the C-25 allele. However, two-locus analysis revealed that this association was secondary to the classical association with HLA-DRB1. For TNF, located 0.7 Mb telomeric of NOTCH4, SNPs at positions -308 and -238 were studied in the same dataset. We found no association between these TNFalpha gene polymorphisms and MS in this dataset, although there was linkage disequilibrium (LD) between DRB1 and TNF and between HLA-A and TNF. We conclude that alleles of the NOTCH4 and TNFalpha genes are unlikely to be of importance for the susceptibility to MS, although specific alleles of these genes are often carried on the same haplotype as DR15, DQ6.

Cis-acting sequences from the rat cytochrome P450 2B1 gene confer pulmonary and phenobarbital-inducible expression in transgenic mice.

Specific cytochrome P450 enzymes show tissue-specific induction, and different regulatory units for expression of these enzymes have been identified. The regulation of the phenobarbital (PB)-inducible P450 genes has been relatively well characterized in terms of PB induction, but less so with regard to tissue-specific expression. CYP2B2 is not expressed in the rat lung, whereas cytochrome P450 2B1 (CYP2B1) is a dominating enzyme in the same tissue. The constitutive expression of CYP2B1 and CYP2B2 in liver is low, but inducible by PB, whereas the pulmonary expression of CYP2B1 is not induced by PB. This indicates utilization of different regulating mechanisms in the two organs. A gene construct consisting of the structural gene for LacZ coupled to a 1.3-kb 5' fragment of the rat CYP2B1 gene was used to generate transgenic mice in order to further elucidate the mechanism behind tissue-specific expression and PB induction of the CYP2B1 gene. Using reverse transcriptase-polymerase chain reaction on total RNA extracted from lung and liver tissue, a lung-specific transcription of the transgene was observed. Transcription of the construct was also observed in livers from PB-treated transgenic animals. By histochemical staining of lung sections with 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-gal), we demonstrated expression at the protein level in bronchiolar cells. In conclusion, our results revealed that the region extending to -1. 3 kb in the 5' flanking region of the CYP2B1 gene included sequences that could partly account for the lung-specific transcription of CYP2B1 and the hepatic induction of CYP2B1 transcription by PB.