D-glycerate dehydrogenase deficiency (or 3-phosphoglycerate dehydrogenase deficiency, PHGDH deficiency, PHGDHD) is a rare autosomal metabolic disease where the young patient is unable to produce an enzyme necessary to convert 3-phosphoglycerate into 3-phosphohydroxypyruvate, which is the only way for humans to synthesize serine.

[4] 3-Phosphoglycerate dehydrogenase catalyzes the transition of 3-phosphoglycerate into 3-phosphohydroxypyruvate, which is the committed step in the phosphorylated pathway of L-serine biosynthesis.

It is also essential in cysteine and glycine synthesis, which lie further downstream.

Nonetheless, the phosphorylated pathway that PHGDH participates in is still suspected to have an essential role in serine synthesis used in the developmental signaling of plants.

[6][7] Treatment typically involves oral supplementation of serine and glycine.