(A,B) IMPDH monomer with the catalytic domain in green and regulatory domain in pink. Regulatory domain is bound to two GTP molecules in dark blue and one ATP in light blue. (A) IMPDH1 (7rfg) with RP mutations in orange that cluster around the nucleotide binding sites. (B) IMPDH2 (6u9o) with neurodevelopmental mutations in red that cluster around the nucleotide binding sites.