Hemoglobin Genotype Frequencies in Lagos: Insights From Offspring of Hemoglobin AS Mothers

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Introduction Sickle cell disease (SCD) is a genetic disorder with a high disease burden in many parts of sub-Saharan Africa. The disease follows an autosomal recessive inheritance pattern, and its persistence within populations is influenced by various genetic, biological, and environmental factors. In regions where carrier status is common, understanding hemoglobin (Hb) genotype distributions among newborns, particularly those born to Hb AS mothers, is crucial for genetic counseling and public health interventions. This study examines Hb genotype distributions and allele frequencies in neonates of Hb AS mothers in Lagos, Nigeria, and compares the observed distributions with Hardy-Weinberg Equilibrium (HWE) expectations derived from population-level allele frequencies. Methods A descriptive cross-sectional study was conducted at Alimosho General Hospital in Lagos, Nigeria. Blood samples were collected from 404 neonates born to Hb AS mothers and analyzed for Hb genotypes using the HemoTypeSC point-of-care test, while blood samples from mothers were assessed using cellulose acetate Hb electrophoresis and sickling test. Allele and genotype frequencies were calculated from observed distributions and compared with expected values under HWE. Expected genotype frequencies were derived using population-level allele frequencies as a reference model. Fisher’s exact and binomial tests (with 95% confidence intervals (CIs)) were applied to assess deviations between observed and expected values, with p < 0.05 considered statistically significant. Results Among 404 neonates born to Hb AS mothers, 190 (47.0%) had Hb AA, 188 (46.5%) had Hb AS, 20 (5.0%) had Hb SS, 5 (1.2%) had Hb AC, and 1 (0.2%) had Hb SC. Corresponding allele frequencies were Hb A: 0.709, Hb S: 0.284, and Hb C: 0.007. No significant deviation from the model-based expectations under HWE was observed (observed 5.0% vs expected 8.1%; p > 0.05). However, the combined frequency of high-risk genotypes (Hb SS and Hb SC) was 5.2% (95% CI: 3.2-7.9%), significantly lower than the 8.5% expected (p = 0.017). Discussion The observed Hb frequencies align closely with Hardy-Weinberg expectations, suggesting approximate equilibrium in this cohort. The slightly lower occurrence of high-risk genotypes (Hb SS and Hb SC) than predicted under the model (p = 0.017) may indicate subtle deviations from random mating, possibly influenced by partner selection preferences within the population. Although paternal genotypes were not determined, these findings provide useful insight into the potential value of strengthening premarital and antenatal genotype screening. Conclusion This study contributes to understanding Hb genotype inheritance among neonates of Hb AS mothers in Lagos. While genotype distributions largely followed Hardy-Weinberg expectations, findings point to possible social influences on mating patterns that warrant further exploration. Broader, couple-based, and population-level studies, incorporating paternal genotypes, are recommended to clarify the role of selective mating and demographic dynamics on genotype patterns in high-prevalence settings.

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