CTPS2

CTP synthase 2 catalyzes the rate-limiting step in cytosine nucleotide synthesis, converting UTP to CTP for DNA, RNA, and phospholipid production. Biallelic mutations cause autosomal recessive developmental and epileptic encephalopathy with onset in infancy, characterized by severe intellectual disability, refractory seizures, and cortical visual impairment. The gene is highly constrained against loss-of-function variants, reflecting its essential role in nucleotide metabolism.