This is a data linking paper that looks at medication prescription and consanguionous marriages. In the introduction, they note that for Roman Catholics, cousing marriage requires a specail dispensation, and the rate of such in Ireland is 1 in 625. This appears, from a national database to be the rate in Ireland.
I would add that Northern Irelanad is cold, bleak, Calvinist and heavily medicated.
Of the 363?960 individuals born between 1971 and 1986 in our cohort (52.5% [191?102] male), 609 (0.2%) were born to consanguineous parents, including 349 to second-cousin consanguineous parents and 260 to first-cousin consanguineous parents.
There was a clear stepwise increase in the proportion of consanguineous offspring in receipt of psychotropic medication with degree of consanguinity. More than one-third (35.8% [93 of 260]) of children of first-cousin consanguineous unions were in receipt of antidepressant or anxiolytic medications compared with just over one-quarter (26.0% [89?412 of 344?183]) of nonrelated offspring. Furthermore, 8.5% (22 of 260) of first-cousin consanguineous parent offspring were in receipt of antipsychotic medication compared with 4.3% (15 of 349) of second-cousin consanguineous parent offspring and 2.7% (9167 of 344?183) of nonrelated offspring.
Maguire A, Tseliou F, O’Reilly D. Consanguineous Marriage and the Psychopathology of ProgenyA Population-wide Data Linkage Study . JAMA Psychiatry. 2018;75(5):438–446. >
The authors correctly note that they are using antidepressants as a proxy measure for common mental disorders, as the SSRIs are used to treat both. However, using antipsychotics for serious mental disorders may not work as well, as they have started to be used in many places instrad of benzodiazepines to manage anxiety, despite increased risks.
But it appears that the Papists and Presbyterians are right. Cousin marriages are to be discouraged.