This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
All of the following intercellular communications occur extracellular chemical messengers except 
Select and explain. 
A. Paracrine, B. Gap junctions, C. Neurohormones, D. Autocrine
B: Gap junctions
Answer: B: Gap junctions 
Explanation: Gap junctions form direct intercellular communications and donot require extracellular chemical messengers as seen in indirect communication. Gap junctions are made of connexons. Each connexon is made up of six proteins subunits called connexins. Mutation in the gene coding for connexon causes Clouston syndrome Erythrokeratodermia variable Inherited deafness X-linked Charcot Marie Tooth Disease Predisposition to atherosclerosis , myoclonic epilepsy, cataract Ref: Harper's Illustrated Biochemistry 30th edition Pgno: 494