CF is known to occur in only 20 families (pedigrees) in Finland. Evolution
The ΔF508 mutation is estimated to be up to 52,000 years old. Numerous hypotheses have been advanced as to why such a lethal mutation has persisted and spread in the human population. Other common autosomal recessive diseases such as sickle-cell anemia have been found to protect carriers from other diseases, an evolutionary trade-off known as heterozygote advantage. Resistance to the following have all been proposed as possible sources of heterozygote advantage:

Cholera: With the discovery that cholera toxin requires normal host CFTR proteins to function properly, it was hypothesized that carriers of mutant CFTR genes benefited from resistance to cholera and other causes of diarrhea. Further studies have not confirmed this hypothesis. Typhoid: Normal CFTR proteins are also essential for the entry of Salmonella Typhi into cells, suggesting that carriers of mutant CFTR genes might be resistant to typhoid fever. No in vivo study has yet confirmed this. In both cases, the low level of cystic fibrosis outside of Europe, in places where both cholera and typhoid fever are endemic, is not immediately explicable. Diarrhea: The prevalence of CF in Europe might be connected with the development of cattle domestication. In this hypothesis, carriers of a single mutant CFTR had some protection from diarrhea caused by lactose intolerance, before the mutations that created lactose tolerance appeared. Tuberculosis: Another possible explanation is that carriers of the gene could have some resistance to tuberculosis.
Delusional: This is the most common type of taijin kyofusho and is the most similar to social phobia. It is chronic, often begins before the age of 30, and varies in severity from moderate to severe. Phobic with schizophrenia: This is a more complicated disorder. In such cases, rather than a phobia, taijin kyofusho is a manifestation of schizophrenic symptoms. Diagnosis
A person may be diagnosed with taijin kyofusho if they feel as if their attitudes, behavior, and physical characteristics are inadequate in social situations. As a result of these feelings, they also experience persistent suffering in the form of emotional distress through shame, embarrassment, anxiety, fear, and other tense feelings that occur when confronted with social circumstances. In addition, individuals also worry about being unable to maintain healthy relationships with others. When it comes to socializing, taijin kyofusho sufferers avoid painful social and interpersonal situations, while simultaneously being averse to doing so. Those likely to develop taijin kyofusho have more of a temperamental characteristic of being hypochondriacal. The balance between introversion and extroversion in hypochondriacal temperament is geared more towards introversion. The introversion causes sufferers to focus on themself and problems they have, and by fixating on their weaknesses they become more anxious and depressed. Treatment
The standard Japanese treatment for taijin kyofusho is Morita therapy, developed by Shoma Morita in the 1910s as a treatment for the Japanese mental disorders taijin kyofusho and shinkeishitsu (nervousness).