Kinesin family member 21A
The KIF21A gene provides instructions for making a protein that is part of the kinesin family. Many proteins in the kinesin family are essential for the transport of materials within cells. Kinesin proteins function like freight trains that transport cargo along a track-like system made from structures called microtubules. Some kinesins also help maintain microtubules. As well as functioning like a track, microtubules make up the structural framework of cells and help cells move.
The KIF21A protein is found in nerve cells (neurons) and many other cell types. Researchers believe that this protein plays an important role in neuron development by helping control the growth of microtubules. By blocking microtubule growth at critical times, the KIF21A protein may help direct the path of neuron extensions known as axons so they can reach their correct locations. Once in the right position, axons relay messages to and from the brain to control muscle movement and detect sensations such as touch, pain, and heat.
For proper neuron development, the KIF21A protein must be turned on and off at particular times. When a segment of the protein known as the regulatory region interacts with another segment of the protein known as the motor domain, the protein is turned off (which is known as autoinhibition).
At least 12 mutations in the KIF21A gene have been identified in people with congenital fibrosis of the extraocular muscles (CFEOM). These mutations cause the most common form of the disorder, CFEOM1, and are a rare cause of another form of the condition called CFEOM3. Individuals with CFEOM are unable to move their eyes normally. They have difficulty looking upward or, less commonly, side-to-side, and most also have droopy eyelids (ptosis). In addition, people with CFEOM3 can have intellectual disability or other neurological problems.
Each of the known KIF21A gene mutations changes a single protein building block (amino acid) in the KIF21A protein. Most of these changes occur in the regulatory region of the protein. These mutations alter the protein's structure, which interferes with its ability to turn itself off. As a result, the KIF21A protein is always on (constitutively active) and cannot regulate microtubule growth. Without proper control of microtubule elongation, the axons of nerves develop abnormally and do not reach the muscles they control. Nerves in the head and face (cranial nerves) that control muscles that surround the eyes (extraocular muscles) are particularly affected. Problems with cranial nerve development impair extraocular muscle function, resulting in the characteristic features of CFEOM such as restricted eye movement and droopy eyelids.
Fibrosis of extraocular muscles, congenital, 1, autosomal dominant
fibrosis of the extraocular muscles, congenital, 1
KIF21A variant protein
Kinesin-like protein KIF2
Kinesin-like protein KIF21A
Renal carcinoma antigen NY-REN-62