THE INCIDENCE OF ENDOMETRIOSIS AMONG RELATIVES
Who, then, is most likely to be a genetic candidate for the disease? Ten to twenty years ago (perhaps longer), the implicit assumption was that endometriosis was a disease carried by and exclusive to white middle-class women who were under stress and career-oriented. No real data was collected on the incidence of the disease within these women’s families. Researchers simply tended to associate it with women who fit this characteristic scenario, and did not probe any further. The first real study was done privately in 1970 by Dr. Brooks Ranney, a South Dakota gynecologist, who first noticed a distinct biological pattern among his patients with endometriosis—many were related to each other. Dr. Ranney sent questionnaires to these women. Based on their responses, he calculated that 22 percent reported relatives (both near and distant) who had undergone surgery for endometriosis.
How coincidental is endometriosis among female relatives, and were Ranney s figures high or low for the general population? A study at Baylor College of Medicine, in Texas, in which 123 women participated, attempted to provide more conclusive evidence. In this 1980 study, researchers attempted to trace lineage patterns of the disease by classifying female relatives into categories, then looking at their medical histories. “First-degree” relatives were defined as mothers, daughters, and sisters; “second-degree” relatives included maternal grandmothers, aunts, and nieces; and “third-degree” relatives were female first cousins.
The results were telling: overall, the Baylor team estimated that women whose first-degree relatives developed endometriosis are seven times more likely to develop the disease. Of that percentage, severe endometriosis involved 61.1 percent of family-related cases and 23.8 percent of nonfamilial cases. This meant, clearly; that a woman whose mother or sister had severe endometriosis was a high-risk candidate for the disease and should be tested for carry detection and treatment.
In 1986 another study, this one at the Medical College of Wisconsin, expanded on Baylor’s investigation. This team added some interesting points. Of women participating in the study who reported other family members with endometriosis, about 79 percent of the cases involved maternal lineage and 7 percent implicated the father’s side. Of the women studied, nearly 35 percent of mothers and 21 percent of sisters suffered from endometriosis, too. For second-degree relatives, numbers were significantly lower: for grandmothers the numbers were 0.4 percent, and for aunts the percentage tallied at 3.1 percent. (Such low numbers among an older generation do not necessarily mean lower incidence of the disease. This generation observed different conventions: they married younger and bore children at an earlier age. Fewer reported cases may have also had to do with fewer available diagnostic methods decades ago.)
What do these studies tell US about coincidence of the disease in families? A hereditary factor does, obviously, exist, but it is not an exclusive indicator of endometriosis. There is a stronger hereditary predisposition toward menstrual cramps than endometriosis and that endometriosis may evolve with them.
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