Premature ovarian failure.
POF has many causes, including infection, endocrine abnormalities, autoimmune disease, and various treatments for cancer. Each of these conditions has some degree of genetic contribution to disease development. In addition, multiple etiologies of POF are primarily due to an underlying genetic abnormality. Some of these are individually rare gene mutations that most internists are unlikely to encounter in practice. Two particular genetic causes of this condition are common enough to merit consideration in primary care practice.
Sex Chromosome Abnormalities
Turner syndrome, which results from the lack of a second sex chromosome (45, X karyotype), is a well-known cause of POF. Although classic Turner syndrome is unlikely to escape diagnosis early in life, some women have mosaic disease, with only a portion of the cells in their body carrying the abnormality. These women may have only subtle outward clinical features, such as slightly short stature or mildly reduced secondary sex characteristics. Establishing the correct diagnosis enables screening for other manifestations of Turner syndrome, such as aortic abnormalities.
Most guidelines include a karyotype as a routine part of the diagnostic workup for POF. Depending on degree of suspicion, it may be appropriate to perform chromosome analysis on both a blood sample and a tissue sample in order to detect low-level mosaicism.
Another possible karyotype finding could be deletion or rearrangement of an X chromosome. Unlike Turner syndrome, these structural X chromosome abnormalities may be inherited, and thus have implications for the woman's parents, siblings, and/or children.
Rarely, women with secondary amenorrhea due to POF are found to have Y chromosome material in some or all of their cells. This confers increased risk of gonadal cancer, and should prompt consideration of surgical gonadectomy.
Fragile X Syndrome
Fragile X sydrome is the most common inherited cause of mental retardation in boys. The genetics of fragile X syndrome is complex, resulting from large expansions of a trinucleotide (3 base-pair) repeat within the FMRl gene on the X chromosome. This trinucleotide repeat is present in up to 40-50 copies in normal versions of the gene. When amplified to 200 or more copies, it results in the typical manifestations of fragile X syndrome (most often in affected boys, but occasionally in girls).
The intermediate range of 50-200 trinucleotide repeats is called a premutation, because it increases the risk of further expansion and full-blown fragile X syndrome in future generations. Women who carry a premutation in one of their two copies of the FMR1 gene have a 13%-26% risk of developing POF. Looked at the other way, a fragile X premutation is found in up to 7.5% of women with isolated (sporadic) POF, and in up to 13% of women with familial POF (Fertil. Steril. 2007;87:456-65).
Thus, genetic testing of the FMRl gene should also be part of the standard workup for POF. Women found to carry a premutation should be advised that their sons and other male relatives--primarily nephews related through sisters and grandsons related through daughters--are at risk for fragile X syndrome. Their female relatives are also at risk for POF if they carry the premutation.
Collectively, genetic contributions to POF are significant enough that a positive family history is found in about 15% of cases. Additional features to seek in the family history include autoimmune disease and evidence of sex chromosome abnormalities or fragile X syndrome.
Family history data can be useful in at least two ways. When evaluating a woman with secondary amenorrhea, a positive family history may inform the differential diagnosis. Of potentially greater importance is the recognition of a family history of POF in a young, healthy woman. Even if a specific cause of the POF cannot be identified, knowledge of her increased risk for early menopause could be invaluable for anticipatory guidance and family planning.
Additional information about fragile X syndrome is available at www.genetests.org. For more information about POF, see N. Engl. J. Med. 2009;360:606-14; Obstet. Gynecol. 2009;113:1355-63.
BY HOWARD P. LEVY, M.D., PH.D.
DR. LEVY is an assistant professor in the Division of General Internal Medicine and McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University.
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|Title Annotation:||GENETICS IN YOUR PRACTICE|
|Author:||Levy, Howard P.|
|Publication:||Internal Medicine News|
|Article Type:||Clinical report|
|Date:||Oct 1, 2009|
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