6996 Optimal Growth Hormone Response Despite Low Insulin-Like Growth Factor-1: Clinical Picture of an A67T IGF-1 Variant
Authors: Bomberg E M , Wu Z , Motorykin I , Torkelson J , Schmitz N , Drilling A , McPhaul M J , Miller B S 
Published: October 2024

Disclosure: E.M. Bomberg: Research Investigator; Self; Novo Nordisk. Z. Wu: Employee; Self; Quest Diagnostics. I. Motorykin: Employee; Self; Quest Diagnostics. J. Torkelson: None. N. Schmitz: None. A. Drilling: None. M.J. McPhaul: Employee; Self; Quest Diagnostics. B.S. Miller: Advisory Board Member; Self; Abbvie, Ascendis Pharma, Biomarin, Bristol-Myers Squibb, Eton Pharmaceuticals, EMD Serono, Endo Pharmaceuticals, GenSci, Novo Nordisk, Pfizer, Inc., Provention Bio, Sanofi, Tolmar. Consulting Fee; Self; Abbvie, Ascendis Pharma, Biomarin, Bristol-Myers Squibb, Eton Pharmaceuticals, EMD Serono, Endo Pharmaceuticals, GenSci, Provention Bio, Sanofi, Tolmar. Grant Recipient; Self; Alexion Pharmaceuticals, Inc., Abbvie, Aeterna Zentaris, Amicus, Foresee Pharmaceuticals, Lumos Pharma, Lysogene, Novo Nordisk, OPKO Health, Pfizer, Inc., Prevail Therapeutics, Sangamo Therapeutics. Research Investigator; Self; Alexion Pharmaceuticals, Inc., Abbvie, Aeterna Zentaris, Amicus, Foresee Pharmaceuticals, Lumos Pharma, Lysogene, Novo Nordisk, OPKO Health, Pfizer, Inc., Prevail Therapeutics, Sangamo Therapeutics. Speaker; Self; Biomarin, Novo Nordisk, Pfizer, Inc., Tolmar.

Introduction: Insulin-like growth factor-1 (IGF-1) measurements are used for growth hormone (GH) deficiency screening and helpful in monitoring GH treatment effectiveness. However, IGF-1 variants have been reported with mass spectrometry (MS)-based assays, potentially limiting interpretation of reported results. Clinical Case: A 14-year-old male presented for short stature. Evaluation was non-revealing aside from low serum IGF-1 measured via liquid chromatography (LC)-MS assay (58 ng/mL; -3.8 standard deviation score [SDS]), and IGF-Binding Protein 3 (3.7 ug/mL; -1.7 SDS). Height was 148.2 cm (1st percentile, -2.08 SDS; mid-parental height 172.7 cm [31st percentile, -0.48 SDS]), pubertal exam Tanner stage 2, and bone age 2.5 years delayed. A GH stimulation test showed a peak GH of 8.1 ug/L; brain MRI was normal. GH was started at 0.29 mg/kg/wk. One month later, IGF-1 remained low (89 ng/mL; -3.2 SDS) and GH was increased to 0.36 mg/kg/wk, and over time to 0.52 mg/kg/wk due to persistently low IGF-1 (-2.9 to -2.3 SDS), despite reports of good compliance and significant catch-up growth (height increased to 19th percentile, -0.84 SDS). He reported no significant side effects during GH treatment. At 17.5 years old, he returned to clinic reporting self-discontinuing GH 1 month prior. Height was at the 27th percentile (171.5 cm, -0.59 SDS), he was fully pubertal, IGF-1 128 ng/mL (-3.1 SDS), and bone age 1.5 years delayed. Further review of IGF-1 linked reports accompanying lab values directly entered into the electronic health record (EHR; starting 2021) described the presence of a rare heterozygous IGF-1 functional variant with unknown clinical significance based on MS data. Concentration of the variant was expected to be identical to that reported for the wild type IGF-1 protein, potentially explaining the lower than expected values. Analysis of the raw LC-MS data (variant peak at m/z 1098.09, isotopic peak index [IP6], relative retention time [rRT]=0.00 min) was consistent with either an A67T or A70T IGF-1 variant. To resolve this ambiguity, the specimen was reanalyzed with an LC-tandem MS/MS fragmentation method, which identified distinguishing peaks at m/z 503.28 (y5 ion) and 305.18 (y3 ion) characteristic of A67T, a known benign variant. Conclusions: Benign IGF-1 variants should be considered in cases of unexplained low IGF-1 levels, including when these remain low despite increasing GH doses, good adherence, and optimal growth velocity. Presence of IGF-1 variants should not affect GH stimulation results (e.g., GH levels), however, may lower reported IGF-1 levels used to determine need for diagnostic testing and followed when monitoring GH response. Careful review of IGF-1 lab reports and full abstraction of these into the EHR should be performed. Knowing a variant is benign could help providers set lower wild-type IGF-1 targets when monitoring GH response to avoid unnecessarily high GH doses.

Presentation: 6/3/2024