A major insertion accounts for a significant proportion of mutations underlying human lipoprotein lipase deficiency

Lipoprotein lipase (LPL; triacylglyceroprotein acylhydrolase, EC 3.1.1.34) is an important enzyme involved in triacylglycerol metabolism. Primary LPL deficiency is a genetic disorder that is usually manifested by a severe elevation in triacylglycerol levels. We have used a recently isolated LPL cDNA clone to study 15 probands from 11 families with this inherited disorder. Surprisingly, 7 of the probands from 4 families, of different ancestries, had a similar insertion in their LPL gene. In contrast to other human genetic disorders, where insertions are rare causes of mutation, this insertion accounts for a significant proportion of the alleles causing LPL deficiency. Detailed restriction mapping of the insertion revealed that it was unlikely to be a duplication of neighboring DNA and that it was not similar to the consensus sequence of human L1 repetitive elements. This suggests that there must be other mechanisms of insertional mutagenesis in human genetic disease besides transposition of mobile L1 repetitive elements.