Abstract
The insulin-like growth factors IGF1 and IGF2 are closely related proteins that are essential for normal growth and development in humans and other species and play critical roles in many physiological and pathophysiological processes. IGF actions are mediated by transmembrane receptors and modulated by IGF-binding proteins. The importance of IGF actions in human physiology is strengthened by the rarity of inactivating mutations in their genes and by the devastating impact caused by such mutations on normal development and somatic growth. Large-scale genome sequencing has the potential to provide new insights into human variation and disease susceptibility. Toward this end, the availability of DNA sequence data from 60,706 people through the Exome Aggregation Consortium has prompted the analyses presented here. Results reveal a broad range of potential missense and other alterations in the coding regions of every IGF family gene, but the vast majority of predicted changes were uncommon. The total number of different alleles detected per gene in the population varied over an ∼15-fold range, from 57 for IGF1 to 872 for IGF2R, although when corrected for protein length the rate ranged from 0.22 to 0.59 changes/codon among the 11 genes evaluated. Previously characterized disease-causing mutations in IGF2, IGF1R, IGF2R, or IGFALS all were found in the general population but with allele frequencies of <1:30,000. A few new highly prevalent amino acid polymorphisms were also identified. Collectively, these data provide a wealth of opportunities to understand the intricacies of IGF signaling and action in both physiological and pathological contexts.
Highlights
The insulin-like growth factors IGF1 and IGF2 are closely related proteins that are essential for normal growth and development in humans and other species and play critical roles in many physiological and pathophysiological processes
Both IGFs exert their biological effects through binding to the IGF1 receptor (IGF1R), a transmembrane ligand-activated tyrosine-protein kinase related to the insulin receptor (INSR) in amino acid sequence and structure [6, 10, 11]
The IGF2R shares structural elements and functions with the cationdependent mannose 6-phosphate receptor (CDMPR) [13, 16]. Both receptors contain units of ϳ145 amino acids (15 in IGF2R and 1 in CDMPR), and both proteins are responsible for delivery of lysosomal enzymes from their intracellular sites of synthesis to the lysosome [13, 16], only the IGF2R appears capable of internalizing these enzymes from the extracellular space [16]
Summary
0.45 a Based on transcripts used in ExAC database. b Several predicted variants do not correspond with the amino acid sequence of insulin and are not included in the compiled data. B Several predicted variants do not correspond with the amino acid sequence of insulin and are not included in the compiled data. B Three predicted major variants do not correspond with the amino acid sequence of IGFALS and are not included in the compiled data. Results reveal a broad range of potential missense and other alterations in the coding regions of every IGF family gene, with the vast majority of predicted changes being uncommon. Taken together, these data will provide new opportunities to understand the intricacies of IGF signaling and action in physiological and pathological contexts
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