Consanguinity and reproductive health among Arabs

Consanguineous marriages have been practiced since the early existence of modern humans. Until now consanguinity is widely practiced in several global communities with variable rates depending on religion, culture, and geography. Arab populations have a long tradition of consanguinity due to socio-cultural factors. Many Arab countries display some of the highest rates of consanguineous marriages in the world, and specifically first cousin marriages which may reach 25-30% of all marriages. In some countries like Qatar, Yemen, and UAE, consanguinity rates are increasing in the current generation. Research among Arabs and worldwide has indicated that consanguinity could have an effect on some reproductive health parameters such as postnatal mortality and rates of congenital malformations. The association of consanguinity with other reproductive health parameters, such as fertility and fetal wastage, is controversial. The main impact of consanguinity, however, is an increase in the rate of homozygotes for autosomal recessive genetic disorders. Worldwide, known dominant disorders are more numerous than known recessive disorders. However, data on genetic disorders in Arab populations as extracted from the Catalogue of Transmission Genetics in Arabs (CTGA) database indicate a relative abundance of recessive disorders in the region that is clearly associated with the practice of consanguinity

Altered Cohesin Gene Dosage Affects Mammalian Meiotic Chromosome Structure and Behavior

Based on studies in mice and humans, cohesin loss from chromosomes during the period of protracted meiotic arrest appears to play a major role in chromosome segregation errors during female meiosis. In mice, mutations in meiosis-specific cohesin genes cause meiotic disturbances and infertility. However, the more clinically relevant situation, heterozygosity for mutations in these genes, has not been evaluated. We report here evidence from the mouse that partial loss of gene function for either Smc1b or Rec8 causes perturbations in the formation of the synaptonemal complex (SC) and affects both synapsis and recombination between homologs during meiotic prophase. Importantly, these defects increase the frequency of chromosomally abnormal eggs in the adult female. These findings have important implications for humans: they suggest that women who carry mutations or variants that affect cohesin function have an elevated risk of aneuploid pregnancies and may even be at increased risk of transmitting structural chromosome abnormalities

Herkunft numerischer und struktureller Aberrationen des X-Chromosoms

Nachdem 1956 durch Tjio und Levan die Darstellung der Metaphasenchromosomen eingeführt worden war, wurden in kurzer Folge ab 1959 verschiedene menschliche Aneuploidien als Ursache häufiger und z.T. bereits vorher bekannter klinischer Syndrome entdeckt (47,XXY als Ursache des Klinefelter-Syndroms: Jacobs u. Strong 1959; Trisomie 21 beim Down-Syndrom: Lejeune et al. 1959; 45,X als Basis des Turner-Syndroms: Ford et al. 1959). Später stellte sich heraus, daß fast die Hälfte der Patienten mit den klinischen Befunden des Turner-Syndroms 46 Chromosomen besitzt, aber entweder ein Mosaik oder eine strukturelle Aberration eines X-Chromosoms oder beides aufweist (Schmid et al. 1974)