A novel receptor, "LDL-receptor-related protein-5" ("LRP-5"), is provided, along with encoding nucleic acid. The gene is associated with type 1 diabetes (insulin dependent diabetes mellitus), and experimental evidence provides indication that it is the IDDM susceptibility gene IDDM4. In various aspects the invention provides nucleic acid, including coding sequences, oligonucleotide primers and probes, polypeptides, pharmaceutical compositions, methods of diagnosis or prognosis, and other methods relating to and based on the gene, including methods of treatment of diseases in which the gene may be implicated, including autoimmune diseases, such as glomerulonephritis, diseases and disorders involving disruption of endocytosis and/or antigen presentation, diseases and disorders involving cytokine clearance and/or inflammation, viral infection, elevation of free fatty acids or hypercholesterolemia, osteoporosis, Alzheimer's disease, and diabetes.