Also called Mendelian or monogenic disorders. Single gene disorders are caused by mutations that occur in the DNA sequence of a single gene. More than 6,000 human diseases are caused by single gene disorders. They are all individually rare but occur in about 1.4% of the population as a whole and cause a high rate of morbidity and mortality. Single-gene disorders are inherited in recognizable patterns and are classified according to how they are transmitted from one generation to the next. If the mutation is on an autosome, the condition is said to be inherited in an autosomal pattern. If the mutation is on the X-chromosome, the condition is said to be inherited in an X-linked manner. Autosomal dominant, autosomal recessive and X-linked recessive conditions are the most common. X-linked dominant conditions also occur, but are rare.
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