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Restriction isotyping of apolipoprotein E R145C in type III hyperlipoproteinemia
S H Hsia1, P W Connelly, R A Hegele
1Department of Medicine, St. Michael's Hospital, Toronto, Ontario, Canada.
Background:
An adolescent female who presented with type III hyperlipoproteinemia was found to have an E3/2 phenotype by isoelectric focusing while restriction isotyping using HhaI revealed a pattern compatible with classical E3/3. Studies were carried out to determine the nature of the patient's apolipoprotein E abnormality.
Methods:
A 244 bp fragment of exon 4 of apolipoprotein E was amplified by the polymerase chain reaction (PCR). Restriction isotyping was carried out with BbvI and Fnu4HI and results were confirmed by direct sequencing.
Results:
The patient was found to be heterozygous for a C-->T transition at the first base of codon 145, resulting in a substitution of cysteine for arginine (R145C) which completely explained the discrepancy between the isoelectric focusing and HhaI restriction isotyping. We noted that the DNA change altered palindromic recognition sites for the endonucleases BbvI and Fnu4HI.
Conclusions:
Digestion with BbvI or Fnu4HI allows for rapid restriction isotyping for the rare apolipoprotein E R145C mutation associated with hyperlipidemia.
