Genetic disorders and Primary Ovarian Insufficiency
There are multiple types of genetic disorders but, as far as feminine fertility is concerned, the most important ones are disorders affecting the X chromosome. The key that this disorders are the principal cause of a phenomenom going by the name of Primary Ovarian Insufficency (POI), also known as Premature Ovarian Failure.
This phenomenon is defined by a loss of ovarian function before menopause, causing irregular periods and a reduction on fertility.

Some examples of genetic disorders affecting the chromosome X and, consequently, causing POI are:
This disorder consists on the parcial or complete lacking of one X chromosome in women. In a 96% of the cases the ovarian function of these patients is altered. Aproximately the 2-7% will be able to conceive spontaneously, but the miscarriage and deformity rates are above-average.
This disorder is a consequence of an excessive number of copies of one mutation on the short arm of the X chromosome. While the normal patients have around 6-50 copies of this mutation, those with 55-200 copies will be considered carriers of this disorder. Women who have this disorder, have more than 200 copies, and are defined by a lower ovarian reserve.