ESPE Abstracts

Acid-labile subunit (ALS) is a glycoprotein, which is produced in the liver in response to growth hormone (GH). The main role of ALS is to form a complex with insulin-like growth factor I (IGF-I) and IGF binding protein-3 (IGFBP-3) in order to extend their circulating half-life and thus support the action of GH. Although the mechanism and the consequences of ALS deficiency are well studied, ALS-deficient patients are still of research interest because of the unclear incidence of the condition among the short-statured population and the need of specific therapeutic approach to these patients.

Objectives: The aim of this study is to assess the prevalence of ALS deficiency in a cohort of patients with GH deficiency (GHD) followed up in a tertiary University pediatric endocrinology center.

Design: Study participants are 71 children (76 % boys, age range 2-18 years), diagnosed with GHD by 2 standard GH stimulation tests (max GH <10 ng/ml). Blood serum samples were collected from each patient during the visits at the center, and then were stored frozen at -80℃ in 0.5 ml aliquots. The analysis was done on a single occasion with standard ALS ELISA kit. The mean age of the children at the time of collection of samples was 11.6±3.3 years, and all patients were on GH therapy.

Results: ALS deficiency screening identified serum ALS levels with range from 2.2 to 60 mg/l, with a mean of 17.4±8.7 mg/l. The mean ALS levels were significantly lower than the published levels from subjects without short stature - 24.2±4.7 mg/l (Baxter, 1990) and 20.3±3.1 mg/l (Juul et. al., 1998), P < 0.05 for both, but close to the levels in the referred for GHD patients (6.5±4.8 mg/l). Very low ALS levels (<4.0 mg/l) were detected in 3 (4.2%) of the patients. The low ALS levels correspond with low SDS_height (-2.82±1.21) and low SDS_IGF-1 (-1.43±1.0) before therapy. In one of the 3 patients, the ALS level (2.2 mg/l) was close to those in patients with IGFALS gene mutations (<1.0 mg/l). The revision of clinical features in this patient showed features than warrant further molecular genetic analysis.

Conclusion: Our results show the prevalence of ALS deficiency in the current GH treated cohort and support the evidence that investigation of ALS levels could be helpful in the differential diagnosis of growth disorders.