2.3: Genetic Disorders
- Page ID
- 10182
Most of the known genetic disorders are dominant gene-linked; however, the vast majority of dominant gene linked disorders are not serious or debilitating. For example, the majority of those with Tourette's Syndrome suffer only minor tics from time to time and can easily control their symptoms. Huntington's Disease is a dominant gene linked disorder that affects the nervous system and is fatal, but does not appear until midlife. Recessive gene disorders, such as cystic fibrosis and sickle-cell anemia, are less common but may actually claim more lives because they are less likely to be detected as people are unaware that they are carriers of the disease. Some genetic disorders are sex-linked; the defective gene is found on the X-chromosome. Males have only one X chromosome so are at greater risk for sex-linked disorders due to a recessive gene, such as hemophilia, color-blindness, and baldness. For females to be affected by the genetic defects, they need to inherit the recessive gene on both X-chromosomes, but if the defective gene is dominant, females can be equally at risk. Table 2.1 lists several genetic disorders.
Recessive disorders (homozygous): the individual inherits a gene change from both parents. If the gene is inherited from just one parent, the person is a carrier and does not have the condition. | Cases per Birth |
---|---|
|
1 in 500 Black births 1 in 36,000 Hispanic births |
|
1 in 3500 |
|
1 in 10,000 |
|
1 in 4000; 1 in 30 American Jews is a carrier; 1 in 20 French Canadians is a carrier |
|
Fewer than 20,000 US cases per year |
Autosomal Dominant Disorders (heterozygous): In order to have the disorder, the individual only needs to inherit the gene change from one parent. | Cases per Birth |
|
1 in 10,000 |
|
1 in 250 |
|
1 in 15,000-40,000 |
Sex-Linked Disorders: When the X chromosome carries the mutated gene, the disorder is referred to as an X-linked disorder. Males are more affected than females because they possess only one X chromosome without an additional X chromosome to counter the harmful gene. | Cases per Birth |
|
1 in 4000 males 1 in 8000 females |
|
1 in 10,000 males |
|
1 in 3500 males |