Identification of Circulating IGF-1 Polymorphisms By High Resolution LC-MS

Program: Abstracts - Orals, Poster Previews, and Posters
Session: SAT 001-027-Growth Disorders, Pediatric Endocrinology, Puberty and Disorders (Posters)
Bench to Bedside
Saturday, April 2, 2016: 1:15 PM-3:15 PM
Exhibit/Poster Hall (BCEC)

Poster Board SAT 017
Zengru Wu*, Heather R Sanders, Nigel J. Clarke, Michael Phillip Caulfield, Richard E. Reitz and Michael J. McPhaul
Quest Diagnostics Nichols Institute, San Juan Capistrano, CA
Quest Diagnostics developed a high resolution, accurate LC-MS assay for IGF-1 in 2012 (1). The assay collects full scan mass spectrometry data, and IGF-1 is quantitated based on the mass of [M+7H]+. In 2015, the Mayo Clinic utilized a similar high resolution method to report the A70T polymorphism (2). The ability to identify IGF-1 polymorphisms may influence the interpretation of IGF-1 test results in a small subset of individuals. In order to determine if our assay could also identify IGF-1 variants, we examined existing spectra from patient samples analyzed by our assay. To understand the IGF-1 polymorphisms at the gene level, we performed database searches (dbSNP and 1000 Genomes) and found 5 reported single nucleotide polymorphisms (SNPs) that result in an amino acid substitution within the 70 amino acid of IGF-1 protein with various minor allele frequencies (MAFs). These SNPs included 2 non-validated SNPs with a single reported incidence (V44M and P66A), 1 validated SNP with a single reported incidence (V17M with 0.02% MAF), and 2 validated SNPs with multiple reported incidences (A67T with 0.4% MAF and A70T with 0.04% MAF). Accurate mass spectra of all these polymorphisms can be monitored by extracting data from the existing full scan mass spectrometry data file. Retrospective analysis of existing spectra from patient samples analyzed in our validated diagnostic laboratory test identified multiple occurrences of observed masses compatible with IGF-1 molecules carrying a single amino acid substitution (alanine to threonine).  As the 2 most frequent IGF-1 polymorphisms reported are both A to T substitutions, it is not possible to distinguish them using this approach. We have not identified other polymorphisms in existing patient spectra yet. The results reported here indicate that our high resolution LC-MS assay for IGF-1 can identify polymorphisms. The modification of our exiting high resolution LC-MS IGF-1 to monitor a broader range of masses will permit the detection of IGF-1 polymorphisms that are expected to exist in nearly 0.5% of the population.

(1) Bystrom et al., PLOS One 2012; 7(9): e43457. (2) Hines et al., Clin Chem 2015;61 (7) :990-991.

Disclosure: ZW: Employee, Quest Diagnostics. HRS: Employee, Quest Diagnostics. NJC: Employee, Quest Diagnostics. MPC: Employee, Quest Diagnostics. RER: Employee, Quest Diagnostics. MJM: Medical Director, Quest Diagnostics Inc..

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