Monitoring and Identifying Insulin-Like Growth Factor 1 Variants by Liquid Chromatography–High-Resolution Mass Spectrometry in a Clinical Laboratory

Protein and peptide hormones often exist as sequence variants with different molecular mass. Monitoring these variants of different molecular mass by mass spectrometry using mass-to-charge (m/z) ratio that is indicative of the wild type may lead to inaccurate quantitative results. However, liquid chromatography-high-resolution mass spectrometry (LC-HRMS)-based techniques can capture these differences and provide an opportunity to resolve, or partially resolve, variant complexity. In this chapter, we describe a general approach for monitoring a set of peptide variants with similar m/z ratios and isotopic envelopes, but different in amino acid sequences. As an example, we use insulin-like growth factor-1 (IGF-1) to demonstrate a DNA database-guided approach to monitor protein variants by LC-HRMS in a clinical laboratory. The workflow is automated and therefore avoids manual calculations that are prone to human error. The method can also monitor multiple IGF-1 variants and discover new ones. It can also provide a profile of a patient's IGF-1 status and be used to explore genotype-phenotype relationships in IGF-1 variants.