<s>[INST] context: Synthesis of collagena. The polypeptide chains of preprocollagen are synthesized on the rough endoplasmic reticulum, and the signal (pre) sequence is cleaved.b. Proline and lysine residues are hydroxylated by a reaction that requires O2 and vitamin C.c. Galactose and glucose are added to hydroxylysine residues.d. The triple helix forms, and procollagen is secreted from the cell and cleaved to form collagen.e. Cross-links are produced. The side chains of lysine and hydroxylysine residues are oxidized to form aldehydes, which can undergo aldol condensation or form Schiff bases with the amino groups of lysine residues.A defect in the synthesis or processing of collagen will lead to a variety of diseases, of which Ehlers-Danlos syndrome is one (osteogenesis imperfecta is another). Parkinson disease is caused by low levels of dopamine in the nervous system. In the initial stages of Parkinson disease, giving dihydroxyphenylalanine (DOPA) can reduce the severity of the symptoms because DOPA can be decarboxylated to form dopamine. DOPA can easily enter the brain, whereas dopamine cannot. Tay-Sachs disease results from an inability to degrade GM2, a ganglioside (it is also a sphingolipid). The enzyme missing is b-hexosaminidase. McArdle disease is caused by a defective muscle glycogen phosphorylase, such that the muscle cannot generate glucose from glycogen, leading to exercise intolerance. Maple syrup urine disease is caused by the lack of branched-chain a-keto acid dehydrogenase activity, a necessary step in the metabolism of the branched-chain amino acids (leucine, isoleucine, and valine). [/INST] question: Ehlers-Danlos syndrome can be caused by a problem with the metabolism of which particular compound. | options: A: Glycogen B: Collagen C: Dopamine D: Valine | answer: B </s>