Human mannan-binding protein (MBP) is a serum lectin participating in the innate immune defence. Low MBP concentrations are explained by the dominant action of a point mutation at codon 54 of the MBP gene in Eskimos, partially in Caucasians, but not in Africans. A previously described point mutation at codon 57 was very frequent (0.23) in East Africans, low in Caucasians (0.02), and absent in Eskimos. The African population only conformed to Hardy-Weinberg expectation when assuming the existence of an unknown allele, which was subsequently found as a point mutation at codon 52. This allele appeared with a relatively high frequency (0.05) in both Africans and Caucasians, but was absent in Eskimos. Hardy-Weinberg equilibrium is now seen in the investigated ethnic groups. All cases of MBP deficiency may be explained by these three variants.

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