posted on 2021-08-17, 18:06authored byIevgen Motorykin, Hua Li, Nigel J. Clarke, Michael J. McPhaul, Zengru Wu
Measuring
insulin-like growth factor-1 (IGF-1) is useful for assessing
and managing growth-related disorders, such as acromegaly and growth
hormone deficiency. High-resolution liquid chromatography–mass
spectrometry (LC–MS) is used for measuring IGF-1 due to its
molecular specificity, quantitative performance, well-characterized
reference materials, and detailed age/sex-specific reference intervals.
However, polymorphisms in the IGF1 gene may cause
mass shifts in the polypeptide, which can impede quantitation and
cause errors in clinical interpretation. We (1) developed a concept
of “isotopic peak index”, which allows simultaneous
monitoring of 15 IGF-1 variants by using only four m/z ratios; (2) developed a “relative retention
time” parameter that allows distinction of previously unresolved
variants; and (3) utilized tandem mass spectrometry (MS/MS) to distinguish
between the most common pair of variants: isobaric A67T and A70T.
All methods were validated with DNA sequencing. This approach identified
six variants from the ExAC database, P66A, A67S, S34N, A38 V, A67T,
and A70T; two previously reported V44M and A67V variants; and discovered
six unreported variants, Y31H, S33P, R50Q, R56K, T41I, and A62T. Major
improvements in our workflow include enhanced automation, avoiding
detailed manual calculations that are prone to human error, and the
ability to monitor more, and discover new, IGF-1 variants. The workflow
provides a profile of a patient’s IGF-1 status and can be used
to explore genotype–phenotype relationships in IGF-1 variants.