Rare diseases prevalence

The definition of what constitutes a rare disease varies in different regions of the world. The prevalence figure accepted in the European Union is no more than five individuals per 10 000 of the EU population. In the United States, it is defined as a disease that affects less than 200 000 of the population. This size of population is approximately equal to a prevalence of 7.5 individuals per 10 000 of the United States population. Similarly, the prevalence figures accepted in Japan and Australia are no more than 4.2 and 1.1 individuals respectively per 10 000 of their corresponding populations. 

The two most severe types of ichthyosis, lamellar ichthyosis (LI) and epidermolytic hyperkeratosis (EHK), are distinct families of diseases with completely different etiologies (see Figure 8.1 and Table 8.3). Nevertheless, LI and EHK have several things in common they are rare, congenital diseases (prevalence <1/100,000) with more or less generalized hyperkeratosis and a defective skin barrier, and they usually demands vigorous therapy. 

Gastwirth, J. L. and Hammick, P. A. (1989). Estimation of the prevalence of a rare disease, preserving the anonymity of the subjects by group testing Application to estimating the prevalence of AIDS antibodies in blood donors. Journal of Statistical Planning and Inference, 22, 15-27. 

The major advantages of cross-sectional surveys are that they are relatively inexpensive and easy to design and can evaluate multiple exposures and outcomes. The major disadvantages are that they provide limited information for establishing causality because they are looking at prevalence cases and do not establish a time sequence of events. They also are not useful for studying rare diseases, diseases of short duration, and rare exposures. 

Narcolepsy is a rare disease characterized by excessive daytime sleepiness. It has a prevalence of 0.05% in the general population and affects an estimated 140,000 people in the United States. In 2002, the FDA approved sodium oxybate (Xyrem ) for the treatment of cataplexy in patients with narcolepsy. The active ingredient in this drug is gamma hydroxybutyrate, or GHB. The development and marketing of sodium oxybate was permitted after a revision of the Date Rape Prevention Act of 2000 (see Chapter 5) that allowed GHB to be legally administered for medical purposes. 

In the United States, rare disease is defined as a disease with a prevalence of less than 200000 patients. Some countries have defined a rare disease based on a prevalence of 0.1-0.5% of the population. A rare disease is sometimes referred to as an orphan disease. An orphan drug is defined as a drug to treat a rare disease. The term orphan drug originated from the belief that there were drugs that no pharmaceutical sponsor wanted to develop and market, and thus they were like homeless orphans. 

Primary hyperoxaluria type I (PH I) (Fig. 20.2) is a rare, autosomal recessive inherited disease caused by a defect in glyoxylate metabolism with low or absent activity of liver-specific peroxisomal ala-nine-glyoxylate aminotransferase (ACT) (Danpure 1989). The AGXT gene is located on chromosome 2q36-37 (Purdue et al. 1991). The disease prevalence is two patients per million population (Kopp and Leumann 1995) in Europe. 

Although there is a rather high prevalence of farmer s lung disease when based solely on symptoms reported in questionnaires, it is a rare disease when strictly defined. In 1986, Terho et al presented a Finnish study of the incidence of hospital-diagnosed and clinically confirmed cases of farmer s lung. They found that in 1980 there were 186 new cases of farmer s lung disease in Finland and that in 1981 there were 153. About two-thirds of the patients were women. The mean annual incidence rate of... 

Although the term orphan disease means many things to many people, it has a relatively well-defined meaning in the biomedic community. For example, in the United States, it is defined as a disease that affects fewer than 200,000 citizens. This includes extremely rare diseases, such as mad cow disease, which is (thankfully ) so rare that only a handful of cases have been diagnosed in the past several decades. It also includes many widespread tropical diseases, such as malaria, which are not particularly prevalent in the United States. 

For those infectious diseases that are transmitted to humans via insect vectors the onset and decline phases of epidemics are rarely observed other than as a reflections of the seasonal variation in the prevalence of the insect. Rather, the disease is endemic within the population group and has a steady incidence of new cases. Diseases such as these are generally controlled by public health measures and environmental control of the vector with vaccination and immunization being deployed to protect individuals (e.g. yellow fever vaccination). 

The prevalence of OA in Caucasians approximates the rate in African Americans, but the latter may experience more severe and disabling disease. Persons of Chinese descent rarely have hip OA they are also less likely to develop hand OA but more likely to develop knee OA.3... 

Classic beri-beri, rarely seen in the United States and Europe, except in alcoholism (P4), is endemic in the Far East because of the prevalent diet of decorticated rice (F6). It occurs in two forms wet beri-beri, characterized by edema and cardiovascular symptoms (G6), and dry beri-beri with peripheral neuritis, paralysis, and atrophy of the muscles. Conditions which may predispose to deficiency by increasing thiamine requirements are pregnancy (see section 2.4), and lactation, hyperthyroidism, malignant disease, febrile conditions, increased muscular activity, high carbohydrate diets, and parenteral administration of glucose solutions. A constant supply of thiamine is required for optimal nutrition because storage in the liver and elsewhere is limited. Thiamine is synthesized by bacteria in the intestinal tract of various animals, but this is not a dependable source for man. 

Alzheimer s disease (AD) is the most frequent cause of dementia (50-70%), followed by vascular dementia (30 0%) and mixed dementia (15-20%). These prevalent forms of age-related neurodegeneration represent a major problem of health in developed countries, with more than 25 million people affected and probably more than 75 million people at risk during the next 20-25 years worldwide. The prevalence of dementia increases exponentially, from approx. 1% at 60-65 yr to more than 30-35% in people older than 80yr. It is very likely that in those patients older than 75-80 yr most cases of dementia are mixed in nature (degenerative plus vascular), whereas pure AD cases are very rare after 80yr (1-3). 

Granulocytic pleocytosis with a prevalence of eosinophils (eosinophilic pleocytosis) This is a relatively rare picture of so-called eosinophilic meningitis, which is not an inflammatory infective disease but a general severe allergic reaction of the body. 

Lysosomal storage diseases are rare, with an estimated birth prevalence of about 1 5000 to 1 7000 newborns. The sphingolipidoses make up about one-half of the total number of patients with lysosomal storage diseases [35, 44, 45]. In some popu-... 

Darier s disease (DD)(MIM 124200) or Darier-White s disease (also referred as keratosis follicularis) is a rare autosomal dominant disease, first described by Darier and White in 1889. DD affects both sexes and all ethnic groups, with a prevalence estimated between 1 in 26 300 and 1 in 100,000 in different countries (Godic et at., 2005), (Tavadia et al., 2002), (Wilkinson, 1977) (Cooper and Burge, 2003 Svendsen and Albrecten, 1959). Penetrance of the disease is complete, and expression is highly variable between and within affected families. 

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