Novel functional APOB mutations outside LDL-binding region causing familial hypercholesterolaemia.
Familial hypercholesterolaemia (FH) is characterized by increased circulating low-density lipoprotein (LDL) cholesterol leading to premature atherosclerosis and coronary heart disease. Although FH is usually caused by mutations in LDLR, mutations in APOB and PCSK9 also cause FH but only a few mutations have been reported, APOB p.R3527Q being the most common. However, 30-80% of clinical FH patients do not present an identifiable mutation in any of the described genes. To identify the genetic cause of the hypercholesterolaemia in 65 patients without mutations in LDLR, PCSK9 or in fragments of exon 26 and 29 of APOB currently analysed, we performed whole sequencing of APOB by pyrosequencing. A total of 10 putative mutations in APOB were identified. Flow cytometry with fluorescently labelled LDL from patients and relatives showed that p.Arg1164Thr (exon 22) and p.Gln4494del (exon 29) presented a 40% decrease in internalization in lymphocytes and HepG2 cells, very similar to APOB3527. The proliferation assays with U937 cells showed reduced growth for both cases. The variant p.Tyr1247Cys was found to be neutral and other three alterations were considered polymorphisms. Our results emphasize the need to study the whole APOB in routine protocols to improve patient identification and cardiovascular risk assessment.
Unidade de I&D, Grupo de Investigação Cardiovascular, Departamento de Promoção da Saúde e Prevenção de Doenças não Transmissíveis, Instituto Nacional de Saúde Dr. Ricardo Jorge, Lisboa, Portugal.
Ana Catarina
AC
Alves
Aitor
A
Etxebarria
Anne Katherine
AK
Soutar
Cesar
C
Martin
Mafalda
M
Bourbon
D000293:Adolescent; D000328:Adult; D000368:Aged; D001055:Apolipoproteins B / Q000235:genetics*; D050197:Atherosclerosis / Q000097:blood / Q000235:genetics; D001483:Base Sequence; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002648:Child; D008078:Cholesterol, LDL / Q000097:blood*; D003327:Coronary Disease / Q000097:blood / Q000235:genetics; D005190:Family; D005260:Female; D020022:Genetic Predisposition to Disease; D056945:Hep G2 Cells; D006801:Humans; D006938:Hyperlipoproteinemia Type II / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D009154:Mutation; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases / Q000235:genetics; D011973:Receptors, LDL / Q000235:genetics*; D017422:Sequence Analysis, DNA; D012697:Serine Endopeptidases / Q000235:genetics; D020298:U937 Cells; D055815:Young Adult
D001055:Apolipoproteins B; D008078:Cholesterol, LDL; C573412:LDLR protein, human; D011973:Receptors, LDL; C472125:PCSK9 protein, human; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases; D012697:Serine Endopeptidases