The majority of insulin-like growth factor (IGF)-I and IGF-II circulate in the serum as a complex with the insulin-like growth factor binding protein (IGFBP)-3 or IGFBP-5, and an acid-labile subunit (ALS). The function of ALS is to prolong the half-life of the IGF-I-IGFBP-3/IGFBP-5 binary complexes. Fourteen different mutations of the human IGFALS gene have been identified in 17 patients, suggesting that ALS deficiency may be prevalent in a subset of patients with extraordinarily low serum levels of IGF-I and IGFBP-3 that remain abnormally low upon growth hormone stimulation. Postnatal growth was clearly affected. Commonly, the height standard deviation score before puberty was between –2 and –3, and approximately 1.4 SD shorter than the midparental height SDS. Pubertal delay was found in 50% of the patients. Circulating IGF-II, IGFBP-1, -2 and -3 levels were reduced, with the greatest reduction observed for IGFBP-3. Insulin insensitivity was a common finding, and some patients presented low bone mineral density. Human ALS deficiency represents a unique condition in which the lack of ALS proteins results in the disruption of the entire IGF circulating system. Despite a profound circulating IGF-I deficiency, there is only a mild impact on postnatal growth. The preserved expression of locally produced IGF-I might be responsible for the preservation of linear growth near normal limits.

Context:To date, 16 IGFALS mutations in 21 patients with acid-labile subunit (ALS) deficiency have been reported. The impact of heterozygosity for IGFALS mutations on growth is unknown. Objective:The study evaluates the impact of heterozygous expression of IGFALS mutations on phenotype based on data collected by the International ALS Consortium. Subjects/Methods: Patient information was derived from the IGFALS Registry, which includes patients with IGFALS mutations and family members who were either heterozygous carriers or homozygous wild-type. Within each family, the effect of IGFALS mutations on stature was analyzed as follows: 1) effect of two mutant alleles (2ALS) vs. wild-type (WT); 2) effect of two mutant alleles vs. one mutant allele (1ALS); and 3) effect of one mutant allele vs. wild-type. The differences in height SD score (HtSDS) were then pooled and evaluated.Results: Mean HtSDS in 2ALS was Ϫ2.31 Ϯ 0.87 (less than Ϫ2 SDS in 62%); in 1ALS, Ϫ0.83 Ϯ 1.34 (less than Ϫ2 SDS in 26%); and in WT, Ϫ1.02 Ϯ 1.04 (less than Ϫ2 SDS in 12.5%). When analyses were performed within individual families and pooled, the difference in mean HtSDS between 2ALS and WT was Ϫ1.93 Ϯ 0.79; between 1ALS and WT, Ϫ0.90 Ϯ 1.53; and between 2ALS and 1ALS, Ϫ1.48 Ϯ 0.83. A total of 16 novel mutations in the IGFALS gene have been discovered in children and adolescents with congenital ALS deficiency, characterized by total ALS and severe circulating IGF-I/IGF binding protein-3 (IGFBP-3) deficiencies. These 21 patients come from 16 families and represent high divergency in ethnicity and countries of residence. The spectrum of IGFALS mutations, both homozygous and compound heterozygous, covers the majority of the 20 leucine-rich repeats (LRR), as well as both the amino and carboxy termini, all of which are encoded by exon 2 of the IGFALS gene. Conclusions: Heterozygosity for IGFALS

Background/Aims: To date, four mutations in the IGFALS gene have been reported. We now describe two children of different ethnic background with total acid-labile subunit (ALS) and severe circulating IGF-I/IGFBP-3 deficiencies resulting from three novel mutations in the IGFALS gene. Patients/Methods: Serum and DNA of patients were analyzed. Results: Case 1 is a 12-year-old boy of Mayan origin. Case 2 is a 5-year-old girl of Jewish/Eastern European (Polish, Russian, Austrian-Hungarian)/Icelandic/European (French, English) ancestry. The reported cases had moderate short stature (–2.91 and –2.14 SDS, respectively), nondetectable serum ALS and extremely low serum concentrations of IGF-I and IGFBP-3. Case 1 harbored a novel homozygous 1308_1316 dup9 mutation in a highly conserved leucine-rich repeat (LRR) 17 motif of exon 2, representing an in-frame insertion of 3 amino acids, LEL. Case 2 harbored a novel heterozygous C60S/L244F mutation in exon 2, located within a highly conserved LRR 1 and LRR 9, respectively. Conclusions: The identification of additional novel IGFALS mutations, resulting in severe IGF-I/IGFBP-3 and ALS deficiencies, supports IGFALS as a candidate gene of the GH/IGF system, implicated in the pathogenesis of primary IGF deficiency, and represents an important part of its differential diagnosis.

No abstract