8015 Growth Hormone Axis Dysfunction in PMM2-CDG: Exploring the Role of Dynamic Tests for the Management of Short Stature in Two Pediatric Cases
Authors: Del Medico Giulia , Procopio Elena , Ferri Lorenzo , Barbato Alessandro , Morrone Amelia , Stagi Stefano 
Published: October 2024

Abstract
Disclosure: G. Del Medico: None. E. Procopio: None. L. Ferri: None. A. Barbato: None. A. Morrone: None. S. Stagi: None.
PMM2-CDG is the most prevalent congenital disorder of glycosylation (CDG) and is caused by defective phosphomannomutase2 (PMM2) activity. According to the 2019 guidelines, approximately half of PMM2-CDG patients exhibit short stature and low serum levels of insulin-like growth factor-1 (IGF-1), IGF binding protein 3 (IGFBP3), and acid-labile subunit (ALS). Despite this, there is no expert consensus on the endocrinological management of this condition. We investigated the growth hormone (GH) axis in two 12-year-old female patients with PMM2-CDG. The first patient was compound heterozygote for the most common PMM2 gene variants in Italy, p.(Leu32Arg) and p.(Arg141His). She presented with short stature (&lt; 2 Standard Deviation Score, SDS) and low serum levels of IGF-1 and IGF-BP3 (&lt; 2.5° for age and sex). Bone age was significantly delayed. Tanner stage was prepubertal. Somatotropic response to GH stimulation testing (Levodopa) was normal. After the IGF-1 generation test with recombinant GH, serum IGF-1 increased by 115%. The second patient was compound heterozygote for the known PMM2 pathogenetic variant p.(Ala108Val) and the novel p.(Thr171Asnfs*11) variant (only case described in literature). She presented short stature (&lt; 2 SDS) with near-to-normal IGF-1 and IGF-BP3 serum levels (2.5° for age and sex). Bone age was slightly delayed. Tanner stage was prepubertal. She also exhibited severe obesity, hypertriglyceridemia, and hepatic steatosis. Her somatotropic response to two GH stimulation tests (Levodopa and Arginine) was deficient, probably because of her significant overweight. IGF-1 serum levels didn’t increase after the IGF-1 generation test. Hypoglycosylation in PMM2-CDG impairs the IGF1 system on multiple levels. It destabilizes the ternary complex formed by IGF-1 and glycoproteins IGFBP3 and ALS, therefore reducing the half-life of circulating IGF-1. Hypoglycosylation also reduces IGF1 production by impairing its precursor proIGF-1Ea and its cellular secretion. As a result, PMM2-CDG patients have GH insensitivity, with normal GH production but low levels of IGF-1. However, there is a lack of information in the literature on the use of dynamic tests and hormonal therapies (GH and rhIGF-1) in CDG. The IGF-1 generation test in our patients showed partial GH sensitivity in the first patient and GH insensitivity in the second patient. These observations suggest variability. Some PMM2-CDG patients may benefit from an extended trial with GH therapy, while for GH-insensitive patients a trial with recombinant IGF-1 might be considered. This is one of the first reports that explores the potential role of dynamic tests in PMM2-CDG. As the biochemical effects of hypoglycosylation on the GH-IGF1 pathway are becoming clearer more clinical research is needed to reach a consensus on the management and treatment of short stature in these patients.
Presentation: 6/3/2024