We found that urea cycle gene Otc, which, like Tspan7, is located on the X chromosome, may be involved in the onset and progression of hydronephrosis (Figure 3, Figure 4, Figure 5 and Figure 6 and Table S2) through its effect on the kidneys via the disruption of the urea cycle in the liver and subsequent ammonia accumulation. Here, OTC is linked to hydronephrosis.