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A novel truncated apolipoprotein B (apo B55) in a patient with familial hypobetalipo‐proteinemia and atypical retinitis pigmentosa
Author(s) -
Talmud Philippa J.,
Converse Carelya,
Krul Elaine,
Huq Luhna,
McIlwaine Gawn G.,
Series John J.,
Boyd Patricia,
Schonfeld Gustav,
Dunning Alison,
Humphries Steve
Publication year - 1992
Publication title -
clinical genetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.543
H-Index - 102
eISSN - 1399-0004
pISSN - 0009-9163
DOI - 10.1111/j.1399-0004.1992.tb03141.x
Subject(s) - proband , retinitis pigmentosa , apolipoprotein b , genetics , biology , microbiology and biotechnology , mutation , allele , stop codon , gene , endocrinology , cholesterol
We have identified an apolipoprotein (apo) B mutation in a patient with an atypical form of retinitis pigmentosa (RP). In the family the eye disease is characterised by late age of onset and autosomal dominant inheritance. In addition to RP, the proband has low total cholesterol (4.5 mmol/1) and LDL‐cholesterol (2.0 mmol/1) levels characteristic of the autosomal codominant apolipoprotein (apo) B deficiency disease hypobetalipoproteinemia (HBL). Using a monoclonal antibody directly against apo B and immunoblots of SDS polyacrylamide gel separated plasma, a normal apo B100 and a truncated apo B species with an estimated size of apo B54 was identified in the proband and his RP‐affected sister. The location of the mutation in the apo B gene was identified using chemical cleavage of mismatch and this was confirmed by direct sequencing of an amplified fragment of DNA spanning the estimated site of the mutation. The mutation is a C→T transition at nucleotide 7692 which changes the CGA arginine 2495 codon to a STOP codon resulting in the premature termination of apo B100. The truncated apo B protein is 2494 amino acids long with a predicted size of apo B55. Using allele specific oligonucleotides and oligonucleotide melting techniques, the proband, his sister and two other relatives out of a total of 20 family members, screened for the presence of the apo B55 mutation, were heterozygous for the mutation. The segregation of the apo B55 allele was confirmed in the family using the 3′ variable number of tandem repeats of the apo B gene. The RP‐affected brother of the proband did not have the apo B mutation, and thus we conclude that the eye disease in this family is not co‐segregating with the HBL. The possible effect of the lipid abnormality on the development of RP in this family is discussed.