Notably, the majority of studies in Table 1– including all studies based on Caucasian samples – found only the S and L alleles. The few studies that found alleles longer than L are from East Asian (Chinese or Japanese), African or African-American populations. Four of the six Japanese samples found individuals carrying an XL allele. In the SEBAS sample, almost 9% (95% C.I. 7.1–10.6%) carries an XL allele, a prevalence greater than those in other East Asian samples; only two studies report a higher frequency, and these are based on very small samples of Africans [4] and African-Americans [3].
