diseases. as of 2014, around 5% of the qatari population suffered from hereditary hearing loss; most were descendants of a consanguineous relationship. royalty and nobility carlos ii, a member of the famously inbred habsburgs with an extremely pronounced lower jaw. inter-nobility marriage was used as a method of forming political alliances among elites. these ties were often sealed only upon the birth of progeny within the arranged marriage. thus marriage was seen as a union of lines of nobility and not as a contract between individuals. royal intermarriage was often practiced among european royal families, usually for interests of state. over time, due to the relatively limited number of potential consorts, the gene pool of many ruling families grew progressively smaller, until all european royalty was related. this also resulted in many being descended from a certain person through many lines of descent, such as the numerous european royalty and nobility descended from the british queen victoria or king christian ix of denmark. the house of habsburg was known for its intermarriages; the habsburg lip often cited as an ill-effect. the closely related houses of habsburg, bourbon, braganza and wittelsbach also frequently engaged in first-cousin unions as well as the occasional double-cousin and uncle–niece marriages. in ancient egypt, royal women were believed to carry the bloodlines and so it was advantageous for a pharaoh to marry his sister or half-sister; in such cases a special combination between endogamy and polygamy is found. normally, the old ruler's eldest son and daughter (who could be either siblings or half-siblings) became the new rulers. all rulers of the ptolemaic dynasty uninterruptedly from ptolemy iv (ptolemy ii married his sister but had no issue) were married to their brothers and sisters, so as to keep the ptolemaic blood "pure" and to strengthen the line of succession. king tutankhamun's mother is reported to have been the half-sister to his father, cleopatra vii (also called cleopatra vi) and ptolemy xiii, who married and became co-rulers of ancient egypt following their father's death, are the most widely known example.