All inherited characteristics are encoded by genes. Some simply distinguish people from one another, such as hair color. Abnormalities of one or more genes, particularly recessive genes, are fairly common. Every human being carries six to eight abnormal recessive genes, but these genes don't cause cells to act abnormally unless two similar recessive genes are present. Mutations in the CACN family of genes, which provide instructions for making calcium channels, result in genetic disorders known as calcium channelopathies.
L-type Calcium Channels
Calcium channels are ion channels that display selective permeability to calcium ions. When a smooth muscle cell is depolarized by stretching of the cell or autonomic nervous system stimulation, it causes voltage-gated, or L-type, calcium channels to open. This triggers a chain reaction that results in the smooth muscle contracting. L-type calcium channels also affect the cells of skeletal and cardiac striated muscle with the same results. Muscle contraction enables the heart to pump properly and skeletal muscle to allow body movement. Calcium-involved genetic diseases include muscular, neurological, cardiac, and vision syndromes.
Muscular Syndromes
Hypokalemic periodic paralysis is characterized by muscle weakness or paralysis with a matching fall in potassium levels in the blood. Attacks begin in adolescence and are triggered by strenuous exercise, high carbohydrate and high sodium meals, sudden changes in temperature, or even being startled or over-excitement. Lasting anywhere from a few hours to several days, recovery is usually sudden.
Neurological Syndromes
Marked by sporadic bouts of ataxia or severe discoordination, episodic ataxia is an autosomal dominant disorder provoked by stress or heavy exertion, such as exercise. Symptoms can first appear in infancy and attacks may be accompanied by continuous muscle movement called myokymia. Familial hemiplegic migraine sometimes accompanies episodic ataxia and typically includes total or partial paralysis of half the body during the initial aura phase of the migraine.
Timothy Syndrome
Physical malformations, as well as neurological and developmental defects, characterize Timothy syndrome. The most striking sign of the illness is the co-occurrence at birth of syndactyly, or webbing of fingers and toes, and long QT syndrome, an electrical conduction disorder of the heart. Timothy syndrome is initially confirmed with ECG measurements and gene sequencing is used for further diagnosis. Another symptom, autism spectrum disorders, is sometimes noted, but the disease often ends in early death and, since most of the children affected live an average of only 2.5 years, symptoms of autism may not be present.
Vision Disorders
X-linked congenital stationary night blindness is a rare non-progressive retinal disorder that presents in two forms: CSNB1, in which the rod cells of the eye have no measurable response to light and CSNB2, where a response is measurable to some degree. Both forms of the disorder are accompanied by myopia or hyperopia, which can be corrected with prescription glasses, as well as a tendency toward involuntary rapid eye movements or wandering eye.
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