Worldwide, more than 130 million infants are born each year and a considerable number of 13.5 million of these children have inbred parents. The present study aimed to investigate the association between parents’ consanguinity and chronic illness among their children and grandchildren in India. The nationally representative data, Longitudinal Aging Study in India, 2017–2018, Wave 1 was used for the present study. Bivariate analysis, a probit model, and propensity score estimation were employed to conduct the study. The study observed the highest prevalence of consanguinity marriage in the state of Andhra Pradesh (28%) and the lowest in Kerala (5%) among the south Indian States. People who lived in rural areas, belonged to the richer wealth quintile and Hindu religion were the significant predictors of consanguinity marriage in India. For individuals who were in consanguineous marriages, there was 0.85%, 0.84%, 1.57% 0.43%, 0.34%, and 0.14% chances of their children and grandchildren developing psychotic disorders, heart disease, hypertension stroke, cancer, and diabetes, respectively. Moreover, around 4.55% of the individuals have a history of birth defects or congenital disorders. To address the risk of complicated illnesses due to the consanguinity of marriage, medical, genetic, and social counselling services are required.

Using data from the family and genealogical reconstitutions of the Gitano population of 22 contiguous localities in eastern Andalusia, Spain, this study analysed the intensity, structure and historical evolution of consanguinity in 3056 couples formed from 1925 to 2006. Of these unions, 54.8% were consanguineous, and 28.7% involved relatives up to and including second cousins, resulting in a mean coefficient of inbreeding up to the third degree α3 = 12.4 × 10−3. The rest of the consanguineous unions (26.1% of all) involved more-distant relatives, such as third cousins, fourth cousins and so forth. When all consanguinity degrees found in the genealogical reconstitution were considered, the total mean coefficient of inbreeding was αt = 14.8 × 10−3. The merging of families and pedigrees generated a complex genealogical network with many inbreeding loops and important founder effects. This network revealed a high rate (62%) of Multiple Consanguineous Marriages (MCMs) in which second and subsequent consanguineous ties increased inbreeding levels by a fifth (20.5%). The accumulation of multiple degrees of distant relatedness, many of which had little social or biological importance, has contributed to a significant increase in inbreeding rates. Among Gitano people, intra-family marriages have remained common in the last decades, in sharp contrast to other Spanish populations. Hence the highest rates of close consanguinity (34%) and inbreeding (α3 = 14.6 × 10−3) were found in the 1960s, the decade that saw the onset of Spain’s socioeconomic modernization, internationalization and massive migration. These are among the highest rates of inbreeding found in any European population, including the most endogamous Spanish isolates. They reveal marriage strategies not constrained primarily by geographical barriers, but by ethnocultural separation. Interestingly, in recent decades mixed marriages have been increasing rapidly in this minority, although they are compatible with high rates of consanguinity. Gitano secular endogamy is breaking up, but not uniformly.

Consanguineous marriage is preferred in many countries, especially by Muslims. Despite the increasing education rate in Saudi Arabia, the prevalence of consanguineous marriage does not seem to be decreasing as quickly as expected. The present study aimed to investigate the current prevalence of consanguineous marriage among educated married adults in Riyadh and to determine the factors favouring it. The cross-sectional study was conducted in 2017–18 using an online questionnaire. A total of 550 questionnaires were sent to married adults of both sexes and 417 responded, giving a response rate of 75.8%. The questionnaire consisted of two parts: the first section asked for demographic data such as age, sex, educational level, residential area and family size. The second part was about consanguineous marriage and its degree if present, family history of consanguineous marriage and level of awareness of its potential negative impact on offspring. It was found that the prevalence of consanguineous marriage among the participating educated adults was 39.8% and most of these were married to a first cousin. Neither level of education nor age affected the likelihood of consanguineous marriage, but predictors for the practice among the educated participating adults were having a family history of consanguineous marriage, having consanguineous parents and having a personal preference for consanguineous marriage. In conclusion, the prevalence of consanguineous marriage among educated adults in Riyadh was still high in 2018, especially among first-cousin relatives, and this was related to family history and personal preference rather than educational level or age. It is recommended that further research is conducted to assess the level of knowledge about, and attitude towards, consanguineous marriage among adults in Saudi Arabia.