Sequence analysis of coding exons, including flanking intronic regions, as well as the promoter and enhancer region were carried out as described before (Williams et al., 2018 (link)). Sequencing of the regulatory element in the NAGS intron 1 was performed using the BigDye Terminator Cycle Sequencing kit version 1.1 and an ABI 3130 genetic analyzer (Applied Biosystems by Life Technologies Europe BV, Zug, Switzerland) (Williams et al., 2018 (link)) after amplification with 5’-gca gga tac gct gcg ggc tc-3’ and 5’-gtg ggc cag acg tgg tgc tc-3’ primers and following amplification conditions: 15 min initial denaturation at 95°C; 38 cycles of denaturation (20 s at 95°C), annealing (20 s at 58°C) and extension (1 min at 72°C); and a final extension at 72°C for 7 min. If not provided, genomic DNA was extracted from peripheral blood leukocytes.