mia (all types considered together), and good for thyroid cancer.⁵ Survival for pancreatic cancer is so poor that the estimated number of new cases per year can be higher than the estimated number of people surviving at a given time during the year.⁶

The committee found no broad compilation of data on the prevalence or incidence of rare diseases in the United States. It did, however, locate a recent report from Orphanet that lists estimated European prevalence for almost 2,000 rare diseases (out of an estimated 5,000 to 8,000 such conditions) (Orphanet, 2009). The list has much in common with the NIH list of rare conditions cited in Chapter 1. The demography, living conditions, and other characteristics of Europe and the United States likewise have much in common. Thus, despite the limitations discussed below, the committee believes that the overall portrait of rare diseases prevalence in the Orphanet report is likely to approximate that in this country.

Figures 2-1A-D show the distribution of rare conditions according to prevalence as presented in the Orphanet report. They reveal an overall distribution that is highly skewed to very rare conditions. In fact, data for approximately 1,400 of the approximately 2,000 conditions (about 70 percent) consist only of case reports for individuals or families. For the conditions not included in the study, the distribution may be even more skewed given that the project began with what were thought to be the more common rare conditions (Eurodis, 2005).

In general, the limitations of the data in the Orphanet report include the use of single numbers for conditions with widely varying estimates of prevalence in the literature⁷ and the lack of bibliographic citations and explanatory details.⁸ The committee did not systematically check the data presented in the report, but it did note that a few of the listed conditions