1. Some consanguineous relationships involve only people of the same gender.
2. Not all mixed-gender relationships birth biological children.
3. Most births to consanguineous parents do not produce children with significant genetic problems.
Secondly: there is no statistically significant difference in abortion or stillbirth, in the sample resulting from consanguineous marriages, compared to the sample resulting from marriages between non-relatives.
Thirdly: There is a statistical difference between the age of the mother, in the sample resulting from consanguineous marriages and the one resulting from exogamous marriages, and this difference is considered by many scientists as the causative in chromosomal defects.
Fourthly: The researcher analyzed these results by several statistical methods, assuming that consanguineous marriage has an effect in chromosomal defect, but the results repudiated this assumption.
Something else to keep in mind…
But if consanguineous marriage was prohibited in the society or rare, then this prohibition will lead to the survival of many individuals carrying the disease-causing genes. Therefore, the chance for possible intermarriage of two non-relatives carrying the disease-causing genes for a particular disease will be considerable; hence, the emergence of this disease in these communities. The best example of this disease is Cystic Fibrosis of the Pancreas. This disease is governed by a recessive gene, common in Britain, despite the scarcity of consanguineous marriages. This is due to the presence of a high proportion of carriers of the disease-causing gene, as explained previously, which leads to increased chance of intermarriage between the carriers of this disease, and therefore its manifestation among their progeny.