Diagnosis scoring for clinical identification of children with heterozygous familial hypercholesterolemia.

BACKGROUND: Familial hypercholesterolemia (FH) is a frequent monogenic condition characterized by progressive atherosclerosis requiring preventive therapy from childhood. In a pediatric setting, heterozygous FH (hFH) in children may not be identified from common forms of hypercholesterolemia (HC). OBJECTIVE: To elaborate a clinical scoring system for the diagnosis of hFH, defined by the presence of a disease-causing mutation of the gene for the low-density lipoprotein receptor (LDLR). PATIENTS AND METHODS: A total of 100 unrelated children (6 +/-3 years old, 43 boys, 57 girls) with type IIa HC (LDLC >130 mg/dL) and complete genetic testing (at loci for genes for LDLR, apolipoprotein B, proprotein convertase subtilisin-like kesin type 9, and apolipoprotein E) were selected for score elaboration. Of 60 criteria from clinical records and family questionnaires, predictors of having hFH were estimated by logistic regression analysis. Scores were validated in 38 other unrelated children with HC. RESULTS: Three independent predictors of hFH were identified according to the LDLR genotype (50 Microt+/50 Microt-): low-density lipoprotein cholesterol before (262 vs 178 mg/dL, P < 0.001) and after (225 vs 142 mg/dL, P < 0.001) 3 months or more of a lipid-lowering diet, combined with parental statin usage (odds ratio 6.2; 95% confidence interval 1.4-28.3; P = 0.018). High precision and accuracy of the scoring system (area under the receiver operating characteristic curve = 0.94; 95% confidence interval 0.91-0.98) were translated into 4 probability classes (definite/probable/possible/improbable hFH) with a false-negative rate of 12%. CONCLUSIONS: A score distinguishing hFH from common HC provides a simple tool for appropriate clinical decision and care in high-risk children.

Intronic mutations outside of Alu-repeat-rich domains of the LDL receptor gene are a cause of familial hypercholesterolemia.

Familial hypercholesterolemia (FH), a frequent monogenic condition complicated by premature cardiovascular disease, is characterized by high allelic heterogeneity at the low-density lipoprotein receptor ( LDLR) locus. Despite more than a decade of genetic testing, knowledge about intronic disease-causing mutations has remained limited because of lack of available genomic sequences. Based on the finding from bioinformatic analysis that Alu repeats represent 85% of LDLR intronic sequences outside exon-intron junctions, we designed a strategy to improve the exploration of genomic regions in the vicinity of exons in 110 FH subjects from an admixed population. In the first group of 42 patients of negative mutation carriers, as previously established by former screening strategies (denaturing gradient gel electrophoresis, DNA sequencing with former primers overlapping splice-sites, Southern Blotting), about half ( n=22) were found to be carriers of at least one heterozygous mutation. Among a second group of 68 newly recruited patients, 27% of mutation carriers ( n=37) had a splicing regulatory mutation. Overall, out of the 54 mutations identified, 13 were intronic, and 18 were novel, out of which nearly half were intronic. Two novel intronic mutations (IVS8-10G-->A within the polypyrimidine tract and IVS7+10G-->A downstream of donor site) might create potential aberrant splice sites according to neural-network computed estimation, contrary to 31 common single nucleotide variations also identified at exon-intron junctions. This new strategy of detecting the most likely disease-causing LDLR mutations outside of Alu-rich genomic regions reveals that intronic mutations may have a greater impact than previously reported on the molecular basis of FH.