The insulin-like growth factors (IGFs) are found in binary complexes with members of IGF-binding protein family (IGFBP-1 to -6). IGFALS is the acid-labile subunit of the IGF binding protein complex that forms ternary complexes with IGFs and IGFBP-3/IGFBP-5. IGFALS has no affinity for free IGFs and has a very low affinity for uncomplexed IGFBP-3/IGFBP-5, but readily binds to the IGFs and IGFBP-3/IGFBP-5 complex, which extends the serum half-lives of IGFs. IGFALS is mainly produced by the liver and is exclusively found in high concentration in postnatal serum. IGFALS production is predominantly stimulated by the growth hormone. Mutations in IGFALS causes ALS, amyotrophic lateral sclerosis, deficiency, which manifests itself as delayed and slow puberty. IGFALS mutations have also been associated with insulin resistance. Mature IGFALS protein is composed of 578 amino acids with 20 leucine-rich repeats. It shares 93% identity between mouse and rat, and 79% between mouse and human.