Table 6.

Comparison of characteristics of recessive disorders in populations with random partner choice and populations with customary consanguineous marriage

Random partner choice	Customary consanguineous marriage
Occur unpredictably and sporadically	Often occur in identifiable extended families
Diagnosis of first affected identifies an at-risk couple	Diagnosis of first affected identifies a large family grouping at increased risk.
∼30 % of extended family are carriersa	∼30 % of extended family are carriers
Carriers usually at low risk (usually <2 %) of marrying another carrier	Carriers marrying within the family have ∼30 % risk of marrying another carrier
Usually caused by two different variants of the same gene (dependent on relative frequency of variants)	Usually caused by two identical variants of the same gene
Marriages with unrelated people blend extended families into the wider community.	Frequent consanguineous marriages maintain extended family structures, contacts and communication.

^aAhmed S, Saleem M, Modell B, Petrou M (Ahmed et al. 2002) Screening extended families for genetic counselling for genetic haemoglobin disorders in Pakistan. N Engl J Med 347(15):1162–1168