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Hyperprolinemia is an excess of a particular protein building block (amino acid), called proline, in the blood. This condition generally occurs when proline is not broken down properly by the body. There are two forms of hyperprolinemia, called type I and type II.

People with hyperprolinemia type I often do not show any symptoms, although they have proline levels in their blood between 3 and 10 times the normal level. Some individuals with hyperprolinemia type I exhibit seizures, intellectual disability, or other neurological or psychiatric problems.

Hyperprolinemia type II results in proline levels in the blood between 10 and 15 times higher than normal, and high levels of a related compound called pyrroline-5-carboxylate. This form of the disorder is more likely than type I to involve seizures or intellectual disability that vary in severity.

Hyperprolinemia can also occur with other conditions, such as malnutrition or liver disease. In particular, individuals with conditions that cause elevated levels of a chemical called lactic acid in the blood (lactic acidosis) may have hyperprolinemia as well, because lactic acid stops (inhibits) the breakdown of proline.


It is difficult to determine the prevalence of hyperprolinemia type I because most people with the condition do not have any symptoms. Hyperprolinemia type II is thought to be a rare condition; its prevalence is also unknown.


Hyperprolinemia is caused by variants (also known as mutations) in the ALDH4A1 and PRODH genes. These genes provide instructions for enzymes that break down proline. 

Hyperprolinemia type I is caused by variants in the PRODH gene, which provides instructions for producing an enzyme called proline dehydrogenase. This enzyme begins the process of breaking down proline by starting the reaction that converts proline to pyrroline-5-carboxylate. 

Hyperprolinemia type II is caused by variants in the ALDH4A1 gene, which provides instructions for producing the enzyme pyrroline-5-carboxylate dehydrogenase. This enzyme helps to break down the pyrroline-5-carboxylate produced in the previous reaction, converting it to the amino acid glutamate. 

The conversion of proline to glutamate (and the conversion of glutamate to proline, which is controlled by different enzymes) is important for maintaining a supply of amino acids needed for protein production, and for energy transfer within the cell.

Variants in either the PRODH or ALDH4A1 gene can cause a reduction in proline dehydrogenase or pyrroline-5-carboxylate dehydrogenase function and a decrease in the breakdown of proline. As a result, there is a buildup of proline in the body, leading to hyperprolinemia.


This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have variants. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but do not show signs and symptoms of the condition. In about one-third of cases, individuals carrying one copy of an altered PRODH gene have moderately elevated levels of proline in their blood, but these levels do not cause any health problems. Individuals with one altered ALDH4A1 gene have normal levels of proline in their blood.

Other Names for This Condition

  • Proline oxidase deficiency
  • Prolinemia
  • Pyrroline carboxylate dehydrogenase deficiency
  • Pyrroline-5-carboxylate dehydrogenase deficiency

Additional Information & Resources

Genetic and Rare Diseases Information Center

Patient Support and Advocacy Resources

Clinical Trials

Scientific Articles on PubMed


  • Campbell HD, Webb GC, Young IG. A human homologue of the Drosophila melanogaster sluggish-A (proline oxidase) gene maps to 22q11.2, and is a candidate gene for type-I hyperprolinaemia. Hum Genet. 1997 Nov;101(1):69-74. doi: 10.1007/s004390050589. Citation on PubMed
  • Di Rosa G, Nicotera AG, Lenzo P, Spano M, Tortorella G. Long-term neuropsychiatric follow-up in hyperprolinemia type I. Psychiatr Genet. 2014 Aug;24(4):172-5. doi: 10.1097/YPG.0000000000000037. Citation on PubMed
  • Geraghty MT, Vaughn D, Nicholson AJ, Lin WW, Jimenez-Sanchez G, Obie C, Flynn MP, Valle D, Hu CA. Mutations in the Delta1-pyrroline 5-carboxylate dehydrogenase gene cause type II hyperprolinemia. Hum Mol Genet. 1998 Sep;7(9):1411-5. doi: 10.1093/hmg/7.9.1411. Citation on PubMed
  • Humbertclaude V, Rivier F, Roubertie A, Echenne B, Bellet H, Vallat C, Morin D. Is hyperprolinemia type I actually a benign trait? Report of a case with severe neurologic involvement and vigabatrin intolerance. J Child Neurol. 2001 Aug;16(8):622-3. doi: 10.1177/088307380101600820. Citation on PubMed
  • Jacquet H, Berthelot J, Bonnemains C, Simard G, Saugier-Veber P, Raux G, Campion D, Bonneau D, Frebourg T. The severe form of type I hyperprolinaemia results from homozygous inactivation of the PRODH gene. J Med Genet. 2003 Jan;40(1):e7. doi: 10.1136/jmg.40.1.e7. No abstract available. Citation on PubMed or Free article on PubMed Central
  • Liu LK, Becker DF, Tanner JJ. Structure, function, and mechanism of proline utilization A (PutA). Arch Biochem Biophys. 2017 Oct 15;632:142-157. doi: 10.1016/ Epub 2017 Jul 14. Citation on PubMed
  • Mitsubuchi H, Nakamura K, Matsumoto S, Endo F. Biochemical and clinical features of hereditary hyperprolinemia. Pediatr Int. 2014 Aug;56(4):492-6. doi: 10.1111/ped.12420. Citation on PubMed
  • Shivananda, Christopher R, Kumar P. Type I hyperprolinemia. Indian J Pediatr. 2000 Jul;67(7):541-3. doi: 10.1007/BF02760491. Citation on PubMed
  • Srivastava D, Singh RK, Moxley MA, Henzl MT, Becker DF, Tanner JJ. The three-dimensional structural basis of type II hyperprolinemia. J Mol Biol. 2012 Jul 13;420(3):176-89. doi: 10.1016/j.jmb.2012.04.010. Epub 2012 Apr 16. Citation on PubMed
  • Tanner JJ. Structural Biology of Proline Catabolic Enzymes. Antioxid Redox Signal. 2019 Feb 1;30(4):650-673. doi: 10.1089/ars.2017.7374. Epub 2017 Nov 13. Citation on PubMed
  • van de Ven S, Gardeitchik T, Kouwenberg D, Kluijtmans L, Wevers R, Morava E. Long-term clinical outcome, therapy and mild mitochondrial dysfunction in hyperprolinemia. J Inherit Metab Dis. 2014 May;37(3):383-90. doi: 10.1007/s10545-013-9660-9. Epub 2013 Oct 31. Citation on PubMed

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