Co-segregation studies based on a selection of intragenic
restriction fragment length polymorphisms of the low density lipoprotein
receptor (LDLR) gene have been used extensively both for
research and diagnostic studies of familial hypercholesterolaemia (FH)
families, because direct
mutation screening remains complex. Here we describe the development and
application of a more
efficient approach to co-segregation studies based on highly informative
dinucleotide and
tetranucleotide repeats flanking the LDLR gene. A series of microsatellites
(D19S391, D19S394,
D19S221 and D19S179) were selected for study on the basis of linkage
analysis in the CEPH families
using intragenic polymorphisms for a TA repeat (exon 18) in the LDLR gene,
and earlier data for
a Pvu II polymorphism (intron 15). A physical map of the region of
chromosome 19 also contributed
to this selection. One marker in particular, D19S394, sited 150 kilobases
telomeric to the gene, was
extremely useful, displaying 90% heterozygosity, robust PCR of tetranucleotide
repeats without
stutter bands, and no recombination with the LDLR gene (θ=0, LOD
68).
Use of this marker in the
families of twenty-three FH probands from Hampshire demonstrated co-segregation
of the
hyperlipidaemia phenotype with the LDLR gene region, except in one family
with defective
apolipoprotein B-100, and a family turning out to display familial
combined hyperlipidaemia. This
approach should facilitate the search for any families where FH does not
co-segregate with the
LDLR gene, and will enhance the repertoire of molecular diagnostic tools
available for FH.