Sunday, November 20, 2016

Gap Junctions and Connexin Mutations


Let's start with a brief description of Gap Junctions. Take two empty cardboard boxes, assume they are cells. Bore a hole in each one of them and then enter a small straw in it. Then arrange the two boxes(cells) in such a way that the two straws are aligned perfectly with each other and that their cavities form a continuous column, so that if you pour water in one box it should completely go into the other one without even a single drop falling in between them.



Now terminology, the two straws are called Connexons; and when they are aligned perfectly like I said, they form a Gap Junction. Now connexons are highly symmetrical and elegant structures(Imagine a Hexagon), they are composed of 6 Connexin monomers, which are nothing but integral plasma membrane proteins.
This junction is responsible for the chemical and electrical "coupling" between adjacent cells. A typical example is cardiac muscle cells.

Now Connexin Mutations:
1> Mutations in the Connexin 32 gene are found in X-linked Charcot-Marie-Tooth demyelination neuropathy(remember u have 32 teeth). characterized by progressive degeneration of peripheral nerves, distal muscle weakness and atrophy, impairment of deep tendon reflexes. It is also the most common inherited neuromuscular disorder.

2>Mutations in Connexin 26 gene are associated with deafness. (2+6=8; 8th cranial nerve is the auditory nerve)

3>Mutations in the Connexin 50 gene are associated with congenital cataracts, leading to blindness.
(Remember congenital cataracts can also be caused by TORCH infections; 5 letters)

4>And deletion of the Connexin 43 gene determines skeletal defects and delays in mineralization.

I believe Histology is the most under-estimated subject in our MBBS curriculum and that's sad. So I wrote this article to try to make a infinitesimal part of it interesting.

-VM

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