Journal Article

Molecular Basis of Congenital Lp(A) Deficiency: A Frequent Apo(A) ‘Null’ Mutation in Caucasians

Miroslava Ogorelkova, Alexandra Gruber and Gerd Utermann

in Human Molecular Genetics

Volume 8, issue 11, pages 2087-2096
Published in print October 1999 | ISSN: 0964-6906
Published online October 1999 | e-ISSN: 1460-2083 | DOI: http://dx.doi.org/10.1093/hmg/8.11.2087
Molecular Basis of Congenital Lp(A) Deficiency: A Frequent Apo(A) ‘Null’ Mutation in Caucasians

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High plasma concentrations of lipoprotein(a) [Lp(a)], a covalent low-density lipoprotein-apolipoprotein(a) [apo(a)] complex, are associated with coronary heart disease and stroke. Heritability of Lp(a) levels is high and the major locus determining Lp(a) concentrations is the apo(a) gene. We here demonstrate that a G→A substitution at the +1 donor splice site of the apo(a) kringle (K) IV type 8 intron occurs with a high frequency (∼6%) in Caucasians but not in Africans and is associated with congenital deficiency of Lp(a) in plasma. This mutation alone accounts for a quarter of all ‘null’ apo(a) alleles in Caucasians. RT-PCR analysis based on apo(a) illegitimate transcription in lympho-blastoid cells demonstrated that the donor splice site mutation results in an alternative splicing of the K IV type 8 intron and encodes a truncated form of apo(a). Expression of the alternatively spliced cDNA analogue in HepG2 cells showed that the truncated apo(a) form is secreted but is unable to form the covalent Lp(a) complex. Immunoprecipitated plasma apo(a) from homozygotes for the mutation was almost completely fragmented. Taken together, our data indicate that a failure in complex formation followed by fast degradation in plasma of the truncated free apo(a) is one mechanism which underlies the null Lp(a) type associated with the donor splice site mutation.

Journal Article.  8080 words.  Illustrated.

Subjects: Genetics and Genomics

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