A deletion of one nucleotide results in functional deficiency of apolipoprotein CII (apo CII Toronto).

Apolipoprotein CII Toronto is a mutant non-functional apo CII resulting in apo CII deficiency. A portion of the mutant apo CII gene was cloned into lambda gt10 and subclones were sequenced. A deletion of one base was found in the codon for amino acid Thr68, resulting in alteration of six amino acids and premature termination of the protein at amino acid 74.