Impact of LDLR and PCSK9 pathogenic variants in Japanese heterozygous familial hypercholesterolemia patients.

BACKGROUND AND AIMS: More than 4970 variants in the low-density lipoprotein receptor (LDLR) gene and 350 variants in the proprotein convertase subtilisin/kexin 9 (PCSK9) gene have been reported in familial hypercholesterolemia (FH) patients. However, the effects of these variants on FH pathophysiology have not been fully clarified. We aimed to update the LDLR and PCSK9 variants in Japanese heterozygous FH (HeFH) patients and annotate their clinical significance for the genetic diagnosis of HeFH. METHODS: A genetic analysis of the LDLR and PCSK9 genes was performed in 801 clinically diagnosed HeFH patients. The association of the pathogenic variants with the clinical FH phenotype was examined. RESULTS: Pathogenic variants in the LDLR and PCSK9 genes were found in 46% (n = 296) and 7.8% (n = 51) of unrelated FH patients (n = 650), respectively. The prevalence of Achilles tendon thickness was low (44%) in patients harbouring PCSK9 pathogenic variants. Furthermore, 17% of unrelated FH patients harboured one of five frequent LDLR pathogenic variants: c.1845+2T > C, c.1012T > A: p.(Cys338Ser), c.1297G > C: p.(Asp433His), c.1702C > G: p.(Leu568Val), and c.2431A > T: p.(Lys811*). Patients harbouring the c.1845+2T > C and c.1702C > G: p.(Leu568Val) variants had significantly lower serum LDL-cholesterol levels and higher serum HDL-cholesterol levels, respectively, compared with those harbouring the other LDLR pathogenic variants. The proportion of LDLR pathogenic variants was higher in patients with a younger age of coronary artery disease (CAD) onset and significantly decreased as the age of CAD onset increased. CONCLUSIONS: This study annotated the clinical significance and characteristics of LDLR and PCSK9 pathogenic variants in Japanese HeFH patients.

Proprotein convertase subtilisin/kexin 9 V4I variant with LDLR mutations modifies the phenotype of familial hypercholesterolemia.

BACKGROUND: Familial hypercholesterolemia (FH) is caused by mutations in the genes encoding low-density lipoprotein receptor (LDLR), apolipoprotein B, or proprotein convertase subtilisin/kexin 9 (PCSK9). However, FH shows variability of the clinical phenotype modified by other genetic variants or environmental factors. OBJECTIVE: Our objective was to determine the distribution of PCSK9 variants in Japanese FH heterozygotes and to clarify whether those variants and the combination of those variants and LDLR mutations modify the clinical phenotypes. METHODS: A direct sequence analysis was performed for all 18 exons of LDLR gene and 12 exons of PCSK9 gene in 269 clinically diagnosed FH heterozygotes. The serum lipid levels of the carriers of each variant were compared to those of noncarriers. We also assessed Achilles tendon xanthoma and the prevalence of coronary artery disease (CAD) in the patients aged ≥30 years. RESULTS: Eleven PCSK9 variants were detected. There were 4 frequent PCSK9 variants: L21_22insL, A53 V, V4I, and E32 K. The PCSK9 L21_22insL and A53 V were in linkage disequilibrium with each other. There were no significant differences in serum lipids levels and the prevalence of CAD at the age of ≥ 30 years between PCSK9 V4I, L21_22insL/A53 V, or E32 K variant carriers and noncarriers without LDLR mutations. In the patients carrying LDLR mutations and aged ≥ 30 years, the additional PCSK9 V4I variant was linked to a significantly increased prevalence of CAD in accord with the elevation of the LDL-cholesterol level. CONCLUSIONS: The addition of the PCSK9 V4I was suggested to modify the phenotype of patients carrying LDLR mutations by affecting their LDLR metabolism.

Familial hypercholesterolemia with multiple large tendinous xanthomas and advanced coronary artery atherosclerosis.

We herein report the case of a 53-year-old man with severe coronary ischemia who underwent successful coronary artery bypass surgery. Of note, he had hypercholesterolemia and presented with multiple large tendinous xanthomas and thickened Achilles tendons that had been present for more than two decades. Together with a family history of dyslipidemia, the patient was diagnosed as having familial hypercholesterolemia. Irrespective of an extensive search for possible mutations in the genes presumably involved in the patient's pathophysiology, including low-density lipoprotein receptor (LDLR), proprotein convertase subtilisin/kexin type 9 (PCSK9), autosomal recessive hypercholesterolemia (ARH) and apolipoprotein B (APOB), we were not able to identify the gene mutations responsible for the phenotype observed in the present case.

A novel Thr56Met mutation of the autosomal recessive hypercholesterolemia gene associated with hypercholesterolemia.

AIM: The autosomal recessive hypercholesterolemia (ARH) gene is located on chromosome 1p35 and encodes a 308-amino acid protein containing a phosphotyrosine-binding domain. Several researchers have identified mutations of ARH that cause autosomal recessive hypercholesterolemia; however, it remains unknown whether this gene is involved in common hypercholesterolemia. METHODS AND RESULTS: We searched for polymorphisms of the ARH gene by denaturing high-performance liquid chromatography and direct sequencing. We identified 18 single nucleotide polymorphisms of the gene, including 9 novel polymorphisms, and determined 2 haplotype blocks. No association was observed between common hypercholesterolemia and any polymorphisms or haplotypes of the ARH gene; however, we newly identified a rare Thr56Met missense mutation located in the phosphotyrosine-binding domain, which is the functional domain responsible for cholesterol metabolism. Among 1,800 Japanese individuals enrolled in the Suita study, only 4 were heterozygous for Thr56Met and all had hypercholesterolemia. The total cholesterol level and low-density lipoprotein cholesterol level of diabetic patients with the Thr56Met missense mutation was 276.3+/-13.8 mg/dL and 185.3+/-7.37 mg/dL, respectively. CONCLUSIONS: Because the Thr56Met missense mutation occurs in an orthologously conserved functional domain and all subjects with the mutation had hypercholesterolemia resembling familiar hypercholesterolemia, it may be a cause of familial hypercholesterolemia.