Consanguinity in the Chaouia population (Morocco): prevalence, trends, determinants, fertility, and spontaneous abortions – Egyptian Journal of Medical Human Genetics

From a historical perspective, Chaouia is a Moroccan region located between the plains of Zair in the Northeast and Dokkala in the West, Rehamna in the Southwest. Plains of Tadla and Beni Meskine in the southeast, and bordered by the Atlantic Ocean in the Northwest [13]. In terms of origins, the Chaouia people were described as an intimate mixture of heterogeneous Berber elements strongly arabized and crossed, with a small proportion of Hilalian Arab blood [14].

The term “Chaouia” is derived from the word “chat,” which means “herd owners” or “pastoralists.” This designation could be attributed to the fact that the Marinid Sultanate had their herds maintained by various Chaouia tribes at the end of the fourteenth century. Perhaps this tradition contributed to the term “Chaouia” gaining ethnic significance [13]. The Chaouia region was also known for its agricultural activities and is still considered the breadbasket of the country [15].

The administrative structure of this region changed mainly throughout the years. It adopted an independent tribal societal movement in the earlier centuries. During the French conquest, it was part of useful Morocco (a term applied during the French protectorate to certain Moroccan regions with the greatest resources and potential). Later, between 1971 and 1997, after independence, it was a part of the central region [16]. In 1997, it was part of Chaouia-Ourdigha. In 2015, according to the advanced regionalization division, Chaouia is now part of the region Casablanca-Settat [17].

Field survey

A survey-based cross-sectional study was conducted between January 2019 and January 2020.

Our studied population is divided into three provinces: Settat, Berrchid, and Benslimane, representing the current Chaouia territory (Fig. 1). For a more representative sample of the population, the sample collection was by province using a stratified random sampling approach. Individuals were asked directly in their homes, through one-on-one interviews and collective ones, to verify the information obtained and avoid, as far as possible, any omissions.

Map of the Casablanca-Settat region [40]

Following the provision of informed consent, participants were invited to give information about themselves and their partner’s social and demographic characteristics, including the geographical origin (place of birth), the location of residence of the couple after marriage, urban/rural origin (birth environment), age at first marriage, literacy level, the field of work of the men, the degree of relatedness of the couple, and the first marriage contraction year. Information about the reproductive behavior of couples was also collected, including the number of pregnancies, live births, and spontaneous abortions.

We interviewed 1000 individuals. However, due to memory errors, some participants failed to provide important information required for our study, resulting in incomplete responses during interviews. Therefore, the final sample size was set at 788 for the current study (Table 1).

The inclusion/exclusion criteria

As the study describes a matrimonial practice, our main target population was ever-married individuals. Participants of both genders were included (530 women and 258 men). They were legally adults (18 years or older) and permanent residents of the study area. Indeed, single individuals who had never married and temporary household visitors were excluded from the study. All participants who provided incomplete answers were also excluded.

Data analysis

The coefficient of inbreeding for a child (individual) of a consanguineous marriage is the probability of inheriting two alleles at a locus from a common ancestor and are thus identical by descent [19].

The coefficient is calculated using the following equation [20]:

p: Number of generations between the individual I and the common ancestor from the father’s side A_i. m: Number of generations between the individual I and the common ancestor from the mother’s side A_i. (F_{Ai}): The Inbreeding Coefficient of the ancestor A_i.

Various levels of consanguinity were emphasized including: first cousins (F = 0.0625), double first cousins (F = 0.125), cousins once removed (F = 0.0313), second cousins (F = 0.0156) and distant cousins (F < 0.0156).

At the population level the average inbreeding coefficient (α) was calculated according to the formula [21]:

where (f_{i}) is the relative frequency of individuals with inbreeding coefficient (F_{i}).

In clinical genetics, most marriages are considered consanguineous if the partners are second cousins or closer. The rates of homozygosity in marriages beyond the second cousin (F < 0.0156) present minor differences from those observed in the general population, which may underestimate the actual level of homozygosity [22]. Thus, distant cousins were excluded from the average inbreeding coefficient.

Couples were divided into marriage cohorts based on the year of their first marriage to describe the evolution of consanguineous marriages over time. These periods were chosen based on some key events that occurred in Morocco’s overall territorial development through the years and could have influenced the social behavior of the population.

The association between socioeconomic and demographic characteristics and consanguinity was tested using the chi-square test of independence for categorical data and ANOVA (analysis of variance) for continuous level data. The relationship between consanguinity and the average number of pregnancies, live births, and spontaneous abortions was examined using ANOVA.

Multivariate logistic regression analysis was performed to identify the socioeconomic and demographic characteristics that are predictors or in other words determinants of a consanguineous marriage. The odds ratios were calculated with a 95% confidence interval.

The significance level was set at p < 0.05.