Table 1 Causes of 5-oxoprolinuria beside glutathione synthetase deficiency and 5-oxoprolinase deficiency.

Diet

Certain infant formulas and tomato juice may contain proteins modified by preparation that have increased 5-oxoproline content

[52]

Severe burns Stevens-Johnson syndrome

Increased metabolism of collagen, fibrinogen or other proteins that contain substantial amounts of 5-oxoproline

[53]

Other inborn errors of metabolism

Inborn errors of metabolism not involving the gamma-glutamyl cycle, e.g. X-linked ornithine trancarbamylase deficiency, urea cycle defects, tyrosinemia. In critical organs (e.g. liver, kidney), lack of ATP, which is needed for conversion of 5-oxoproline into glutamate, may lead to 5-oxoprolinuria

[29] [9]

Homocystinuria

Patients with homocystinuria may have excessive formation of 5-oxoproline

[54]

Drug metabolism

Paracetamol, vigabatrin and antibiotics (flucloxacillin, netimicin) probably interact with the gamma-glutamyl cycle

[55-57]

Prematurity

Transient 5-oxoprolinuria has been observed in very preterm infants. The cause is unknown

[58] [29, 59]

Malnutrition, pregnancy

Limited availability of glycine

[60]

Nephropatic cystinosis

Nephropatic cystinosis patients: may have 5-oxoprolinuria probably because of decreased availability of free cysteine, resulting in a secondary impairment of the γ-glutamyl cycle. Cysteamine therapy normalizes the 5-oxoprolinuria

[61]