Adrenoleukodystrophy is a X-linked genetic disease, meaning that the defective gene responsible for the disorder is on the X chromosome.
The letters X and Y represents the last pair of chromosomes. The last two chromosomes are called sex chromosomes, because they determine our gender. Females have two X-chromosomes in every cell, while males have one X-chromosome and one Y-chromosome. The X and Y-chromosomes contain portions that do not match. The genes on these portions are expressed without "competition" from a matching gene on another chromosome.
When gene mutations cause disease, they are referred to as genetic diseases. Gene mutations that are attached to one of the sex chromosomes (often the X chromosome) are referred to as sex-linked. When these mutations cause disease, they are often referred to as sex-linked disorders. If the mutation is on the X-chromosome, it is an X-linked disorder. Most X-linked disorders only affect males, because the unmatched genes on the X-chromosome are expressed without competition from the Y-chromosome.
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