Another year brings us many, many genes closer to understanding the human genetic endowment. Here are a notable few:
Speech: A gene on chromosome 7 has been linked to language development. Carriers of a mutated form of the gene, dubbed SPCH1, have severe difficulties with grammar and language, and their speech is virtually incomprehensible to the untrained ear. Identification of the gene should give researchers insight into the developmental pathways of speech.
Stamina: A gene variant found on chromosome 17 appears to boost physical performance. The gene codes for an enzyme, called ACE, that helps regulate metabolic efficiency. One form of the gene has been linked to increased endurance among high-altitude mountaineers and army recruits who carry it. It's thought that the variant allows carriers to work harder with less fuel.
Psychiatric illness: People with two copies of a mutant gene on chromosome 4 suffer from Wolfram syndrome, a rare neurodegenerative disorder characterized by diabetes, optic nerve atrophy, hallucinations, and progressive dementia. Researchers found that carriers of just one copy of the mutated gene are more likely to be depressed and anxious and are 26 times more likely to undergo psychiatric hospitalization than noncarriers.
Baldness: A mutation of a gene on chromosome 8 causes alopecia universalis, a rare form of baldness. People who have inherited two copies of the mutated gene have no body hair, eyelashes, or eyebrows. The gene, which is expressed in the skin cells and--for reasons unknown --in the brain, apparently turns on other genes involved in the hair-making pathway. The researchers hope that their discovery of the gene, named hairless, will lead to new therapies for other forms of hair loss.
Something altogether different: Red hair, early-onset obesity, and hormonal disruption are symptoms of a disorder first described this past year. The disorder is caused by a mutation of a gene on chromosome 2 that codes for a protein called pre-pro-opiomelanocortin, or POMC. It is normally made into three other proteins, which play a role in hair color, energy storage, and the function of the hormone-secreting adrenal gland. The finding may lead to drugs to correct the disorder.
Fukuyama-type congenital muscular dystrophy: Patients with this disease, one of Japan's most common genetic disorders, suffer from defects in neuronal growth during brain formation as well as progressive muscle degeneration. Researchers have linked it to a mutation in a gene on chromosome 9 that encodes fukutin, a protein involved in nervous system and muscle function. The mutation is apparently caused by a so-called retrotransposon, a roving snippet of genetic information copied into the chromosome 2,000 to 2,500 years ago. This is the first time a human genetic disorder has been linked to a retrotransposon.
Quivering hearts: Idiopathic ventricular fibrillation kills between 15,000 and 36,000 Americans every year. For no apparent reason--and in people with no history of disease--the heart stops beating and begins to quiver. Researchers have now identified a mutant gene on chromosome 3 that may be the cause. The gene codes for ion channels that move sodium across the heart's cell membranes, initiating electric signals and generating heartbeats. Mutations in the gene may disrupt these signals, The discovery should help doctors identify high-risk individuals and prescribe preventive treatment.
Mental retardation: Roughly 1 out, of every 600 men suffers from a genetic form of retardation. The disorder has now been linked to a mutation of a gene on the X chromosome. The gene, called PAK3, seems to be involved in accurate reception of signals by neurons in the brain. Mutations in the gene hinder the normal response of neurons to incoming signals, thus decreasing the neurons' efficiency and leading to learning and behavioral difficulties.
Smell: Scattered throughout our chromosomes are up to 1,000 genes for sensing odors. Most of these genes code for olfactory receptors in the nose, which enable humans to detect about 10,000 different odors. But this past year researchers reported that about 72 percent of the genes are so mutated they're defective. The researchers think the dysfunctional genes accumulated over millions of years, perhaps leading to a gradual blunting of the sense of smell in humans.
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