XDH and xanthinuria type I: Taken together, the findings of the present work, along with those of Iwasaki et al. [37] and Schumann et al. [38], suggest that the impairment of the XDH function in case G2 and the manifestation of type I xanthinuria is due to a severe disruption of the process of biogenesis of XDH, originally caused by the c.449G>T variant.