How would the genetic inheritance of a gene producing abnormal gap junctions affect muscle tissue?

There are choices for this question:

A. All types of muscle tissue would function normally.
B. All types of muscle tissue would function abnormally.
C. Cardiac muscle and some smooth muscle would function abnormally. Skeletal muscle would be
unaffected.
D. Skeletal muscle would function abnormally. Smooth muscle and cardiac muscle would be unaffected.

The correct answer is "cardiac muscle and some smooth muscle will function abnormally. Skeletal muscle would be unaffected". This is because cardiac muscle cells communicates with other cardiac muscle cells through gap junctions (seen histologically as intercalated disks). Smooth muscle cells, similarly, also communicate with other smooth muscle cells through gap junctions. Gap junctions are one form of cell to cell interactions, others are desmosomes, tight junctions, etc. Skeletal muscle cells on the other hand, are long cells (and actually called fibers than cells) and does not need to communicate with other cells through gap junctions therefore are unaffected of the disease. 

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