“…This could be attributed to the lack of confirmation of true positive screens due to failure in claiming a second recall samples, failure to obtain a repeat DBS for those who have been collected before 48 hours of age, or false negative result of the first DBS, which is less likely given the low Met cutoff value used. Further, Kuwait population is heterogenous, composed of different neighboring ethnicities with the majority being expatriates, which could be another reason for the low incidence of HCU compared to the native Qatari population, which is more homogenous and populated by original Qatari tribes and, thus, genetically isolated [7,46]. Nonetheless, the incidence of HCU in Kuwait is relatively high compared to the other parts of the world, where the incidence of HCU reaches 1:260,000 worldwide, 1:222,000 in Latin America [5], 1:1,120,000 in Japan, 1:492,000 in Korea, 1:132,000 in Germany [47], which emphasizes the importance and effectiveness of NBS in our consanguineous population with the increased incidence of autosomal recessive disorders in general and metabolic disorders specifically.…”