This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Medicine
MEDNIK syndrome - which of the following is true 
Select and explain. 
A. Caused by mutations in the AP1S1 gene, B. Disorder of copper metabolism, C. Mental retardation, deafness, neuropathy are seen in this disorder, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: A rare multisystem disorder of copper metabolism with features of both Menke's and Wilson's diseases has been repoed. It is termed the MEDNIK (mental retardation, enteropathy, deafness, neuropathy, ichthyosis, keratodermia) syndrome and is caused by mutations in the AP1S1 gene, which encodes an adaptor protein necessary for intracellular trafficking of copper pump proteins ATP7A (Menke's disease) and ATP7B (Wilson's disease).