G6PD and G6PD deficiency: For studies on an X-linked disorder, such as G6PD deficiency, studies in males would yield a higher number of subjects with the disorder to facilitate the calculation of cut-off threshold of G6PD deficiency while limiting the major confounding factor, i.e., heterozygosity associated with unpredictable G6PD activity in females due to the phenomenon called lyonisation [48–50].