Prolidase Deficiency: A Rare Inherited Cause of Chronic Leg Ulcers

Table of Contents

1. What Prolidase Deficiency Is
2. The PEPD Gene and the Prolidase Enzyme
3. How It Is Inherited
4. The Skin Signs and the Leg Ulcers
5. The Signs Beyond the Skin
6. The Link With Lupus-Like Autoimmune Disease
7. How the Diagnosis Is Made
8. The Long Wait for a Diagnosis
9. Treatments Reported in Case Reports and Case Series
10. What Is Still Not Known
11. Key Research Papers
12. Connections
13. Featured Videos

What Prolidase Deficiency Is

Every day the body takes apart worn-out proteins and reuses their building blocks. Collagen — the tough fibre that holds skin, blood vessels, tendons and bone together — is especially rich in two amino acids, proline and its close relative hydroxyproline. When collagen is broken down, the last pieces left over are tiny two-part fragments (dipeptides) that end in proline or hydroxyproline. One enzyme, prolidase, cuts those last pairs apart so the proline can be used again.

In prolidase deficiency that final cut does not happen. The undigested pairs, called imidodipeptides, build up and pour out in the urine in very large amounts, and the free proline that would have been recycled into new collagen is lost. A 2020 review of every patient with a gene-confirmed diagnosis described the disorder as rare, multisystem and highly variable, with intellectual disability, recurrent infections, an enlarged spleen, skin lesions, autoimmune disorders and low blood counts appearing in different combinations from one person to the next.

The disorder sits at the meeting point of three areas of medicine on this site: skin disease, inherited metabolic disease and immunology. The biochemistry of the enzyme and its connection with the trace mineral manganese is covered in depth on the manganese and wound healing page; this page concentrates on the disease itself and the people who live with it.

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The PEPD Gene and the Prolidase Enzyme

Prolidase is made from instructions in the peptidase D (PEPD) gene. Work in the late 1980s and early 1990s cloned the gene and mapped it to chromosome 19. It is a large gene, spread over more than 130,000 DNA letters and split into 15 segments (exons). The finished enzyme is a pair of identical protein chains, each 492 amino acids long. The same early studies found that the faults in the gene varied from family to family, which is still true today.

The enzyme has a precise job. Laboratory work on the human enzyme describes prolidase as a manganese-dependent dipeptidase: it cuts dipeptides that end in proline or hydroxyproline, and it needs manganese ions to work. In a 2006 study from the University of Pavia, researchers produced human prolidase in both eukaryotic (animal-type) cells and bacteria, purified it, and found it behaved essentially the same as the natural enzyme taken from skin cells. Adding manganese to the incubation helped keep the enzyme active over time. The authors pointed to the bacterially produced enzyme as the most promising starting point for future structural studies and for enzyme replacement therapy — a treatment that so far exists only as a laboratory idea for this disorder.

Not every person with the disorder has exactly zero activity. A 1989 study of skin cells from patients found three different kinds of gene fault, and in cells with no prolidase protein at all, a separate enzyme encoded elsewhere supplied a small amount of similar activity, about 5% of normal, with a different preference for which pairs it cut. The authors proposed that the type of gene fault, together with the amount of this back-up activity, helps explain why the disease is so mild in some people and so severe in others.

Why manganese matters for ordinary wound repair, and how this rare disorder fits that story, is discussed on the manganese pages. The role of the recycled amino acids in building new tissue is covered on the proline and wound healing and collagen pages.

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How It Is Inherited

Prolidase deficiency is autosomal recessive. That means a person has the disorder only when both copies of the PEPD gene — one from each parent — carry a fault. Parents of an affected child usually each carry one faulty copy and one working copy, and they are healthy.

The clinical review in GeneReviews sets out the odds for brothers and sisters of an affected person: at conception each has a 25% chance of being affected, a 50% chance of being a carrier without symptoms, and a 25% chance of being neither affected nor a carrier. Once the family's gene changes are known, the same review notes that carrier testing for relatives and testing during pregnancy are possible. Several reported families are consanguineous (the parents are blood relatives) or come from small, closed communities; the 2012 Israeli study described three unrelated consanguineous families, and a 2006 report described four Amish children from settlements in Ohio who all carried the same single-letter change in both copies of the gene.

Carriers have less enzyme than other people but enough to stay well. A 1979 study of one family measured prolidase in red blood cells: the affected woman had essentially none, while her father and one brother, who did not pass imidodipeptides in their urine, had values between hers and those of healthy adults — the pattern expected of carriers. A 1976 study tested how carriers handle a large protein load. Two children with the disorder, two adult carriers and healthy controls drank gelatin, which is made from collagen. Over the next 24 hours the two children passed 39% and 47% of the hydroxyproline they had swallowed out in their urine still bound up in fragments, compared with 2.7% in healthy children. The two carriers passed only slightly more than healthy adults. In other words, half the gene dose was enough to digest the load almost normally.

The same family study from 1979 held a second surprise: the affected woman's brother also had no measurable enzyme and passed the same fragments in his urine, yet he had no symptoms at all at age 26. That observation, repeated in later families, is part of why the disorder is described as so variable.

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The Skin Signs and the Leg Ulcers

The skin is where prolidase deficiency is most often noticed, and the leg ulcer is its signature. GeneReviews describes the typical ulcers as severe, long-lasting, hard to heal and painful, usually on the lower legs and feet, together with small dilated blood vessels (telangiectasias) on the face and hands. A 1981 report of three patients called the ulcers recalcitrant and listed signs reaching the skin, nervous system, teeth, ears, nose and throat, eyes, bones and joints.

The ulcers can look like more common problems — venous ulcers from varicose veins, livedoid vasculopathy, or pyoderma gangrenosum — and that resemblance is one reason the disorder is missed. A 1999 study of two adult sisters found thickened blood-vessel walls and white blood cells (neutrophils) packed into the ulcer tissue. In the younger sister, the neutrophils' release of a reactive form of oxygen (superoxide) rose and fell with the level of imidodipeptides in her blood, and was highest when her ulcers were most active. The authors proposed that the build-up of these fragments primes white blood cells to damage the skin.

A point that surprises many readers is how often the ulcers are not the first sign. In the 2021 natural-history study, which combined 19 newly described patients with 161 patients from 132 published articles, ulcers were present at the start in only 30% of cases, and the median age at which ulcers began was 12 years. A pair of twins reported in 2022 makes the same point inside one family: both girls carried the same two gene faults and the same facial features, but one developed painful ulcers on her lower legs from age 13 while her sister had no ulcers at all.

Because ulcers that stay open for years carry their own risks, GeneReviews lists a yearly skin examination for signs of cancer forming in long-standing ulcers among the surveillance steps for affected people.

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The Signs Beyond the Skin

Prolidase deficiency is a whole-body disorder. The signs reported across the published cases include:

• Recurrent infections — GeneReviews notes they affect especially the skin and the airways. The four Amish children reported in 2006 first came to medical attention with infection, an enlarged liver and spleen, or low platelets rather than with ulcers.
• An enlarged spleen (splenomegaly), sometimes with an enlarged liver and raised liver enzymes. GeneReviews records that people with an enlarged spleen face a higher risk of the spleen rupturing in contact sports.
• Characteristic facial features — reported again and again as a typical prolidase deficiency face, described in the twin and transplant reports as part of the classic picture.
• Intellectual disability or developmental delay of varying degree, from none to severe. An 8-year-old girl reported in 2012 had the typical face and deep ulcers but normal intelligence.
• Blood and immune findings — anaemia, low platelets, high antibody levels, and low complement were seen in a minority; the Amish children often had asthma-like airway disease and high antibody levels.
• Other findings in a minority of people include skeletal changes and chronic lung disease, according to GeneReviews, which also lists dental problems and refractive eye problems among the issues treated.

The 2021 study also found autoimmune disease in 6 of its 19 patients, including Crohn disease, systemic lupus erythematosus and arthritis, and it recorded a dangerous immune over-reaction, hemophagocytic lymphohistiocytosis (HLH), in which activated immune cells attack the body's own blood cells. The twins reported in 2022 had highly activated inflammatory T cells and exceptionally high blood levels of the inflammatory messenger interleukin-18, which the authors read as a sign of an underlying auto-inflammatory process. Several authors now describe prolidase deficiency as an inborn error of immunity as well as a metabolic disease.

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The Link With Lupus-Like Autoimmune Disease

Of all the immune problems, the tie with lupus — systemic lupus erythematosus (SLE) — is the most striking. Lupus most often begins in young adult women, so its repeated appearance in prolidase deficiency drew attention.

A 2012 study from Northern Israel followed 23 people with prolidase deficiency at one centre and found systemic lupus erythematosus in 3 of them, each from a different family. Searching the medical literature from 1975 to 2011, the same group found 7 more cases of the two conditions together among just under 70 previously reported patients, for 10 in all. The authors concluded that the pairing occurs too often to be a coincidence and proposed that the PEPD gene may act as a genetic risk factor for systemic lupus erythematosus.

A 2023 study from the University of Oxford tested the question of cause directly, in mice. Mice bred without a working prolidase gene developed antibodies against the cell nucleus (the antinuclear antibodies doctors measure in lupus), higher levels of the antibody class IgA in the blood, and immune deposits in the kidneys — a lupus-like disease. In these mice, T cells in the spleen and liver switched themselves on and multiplied without any outside trigger. The authors linked the autoimmunity in prolidase deficiency to this spontaneous T cell activation, probably acting together with other effects of the abnormal metabolism.

The practical side of this link is that a child or young adult can be labelled with lupus, or with another autoimmune disease, before anyone checks the urine for imidodipeptides. A 2023 case report described a woman diagnosed at six with an undifferentiated connective tissue disease, closest to Sjögren syndrome, whose underlying prolidase deficiency was traced to a deletion inside the PEPD gene. The lupus antibody tests themselves are described on the lupus autoantibodies page.

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How the Diagnosis Is Made

Three kinds of test are used, and they confirm one another.

1. Urine imidodipeptides. Because the undigested proline pairs leave the body in the urine, a urine test for them is the classic first clue. In the four Amish children, massive imidodipeptiduria — very large amounts of these pairs in the urine — was present in every case. The 1979 family study identified individual pairs, among them glycyl-proline, in the affected woman's urine.
2. Enzyme activity. Prolidase can be measured in red blood cells or in cultured skin cells. Patients show essentially no activity; carriers show intermediate values. In the Amish children activity was nearly undetectable.
3. Genetic testing. GeneReviews states that the clinical diagnosis rests on typical findings plus imidodipeptiduria or reduced enzyme activity, and that the molecular diagnosis is made when a fault is found in both copies of the PEPD gene. Faults range from single-letter changes to deletions of whole stretches of the gene, and many families carry a change seen nowhere else.

Broad gene testing now finds the disorder directly: in the twins reported in 2022, next-generation sequencing revealed two faults in the PEPD gene, each creating a premature stop signal, and both girls then showed the expected imidodipeptides in their urine.

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The Long Wait for a Diagnosis

The 2021 natural-history study measured the delay directly. Among published patients, half already had symptoms by age 4, yet the average time from first symptoms to diagnosis was 11.6 years. The authors put this down to the fact that the first symptoms are often nonspecific — a chest infection, a large spleen, a rash, slow development — and that the famous leg ulcers usually come later, with a median start at age 12.

The study's authors concluded that prolidase deficiency belongs on the list of disorders to test for in any child with unexplained autoimmunity, ulcers of the lower legs, an enlarged spleen or hemophagocytic lymphohistiocytosis. For families, a late diagnosis also means a late answer about carrier status and about the chance of the disorder in later pregnancies.

Adults are not exempt. The 1979 family study concerned a 23-year-old woman with a chronic leg ulcer, and the 41-year-old man in a 2008 Australian report had lived with leg ulcers and repeated skin infections for most of his life.

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Treatments Reported in Case Reports and Case Series

There is no cure and no standard treatment that has been tested in a clinical trial. The 2022 twin report noted that standard therapies have not been described, and a 2023 report noted there is no consensus on treating the autoimmune features. Everything below comes from single cases or very small series, and what helped one person cannot be assumed to help another.

Topical proline and glycine

The idea behind skin creams containing proline is simple: if the wound is short of recycled proline, supply it directly. In a 1996 Danish study, two ulcers on a 17-year-old girl were treated for 12 weeks with ointments containing 5% proline, or 5% proline plus 5% glycine. Both ointments significantly shrank the ulcers, and the proline-plus-glycine mixture worked faster. In the 2008 Australian report, a 41-year-old man who had been admitted to hospital at least once a year for leg ulcers and cellulitis began a topical 5% proline ointment in a soft paraffin base; the authors reported marked improvement in the ulcers and fewer hospital admissions for cellulitis. GeneReviews records that topical 5% proline, or 5% proline with 5% glycine, applied with dressing changes, has been successful in some affected people. The amino acids themselves are described on the glycine and proline pages.

Vitamin C and manganese

A 1983 report described a woman whose condition improved, both clinically and in her blood and urine tests, after treatment with ascorbate (vitamin C) and manganese. When the researchers then exposed her skin cells to the two substances in the laboratory, only ascorbate appeared to account for the response, apparently by pushing the cells to make more collagen.

Medicines that calm inflammation

• Corticosteroids — in the two adult sisters reported in 1999, moderate oral doses of prednisolone did not help, but high-dose steroid pulses followed by a moderate dose improved the hardened pre-ulcer areas and the ulcers.
• Dapsone was reported as helpful in one of three patients in a 1981 report.
• Topical tacrolimus — a 2019 report described success with tacrolimus ointment on the leg ulcers of a 6-year-old boy who also had Crohn disease.
• Rituximab — in a 28-year-old woman whose ulcers and blood-vessel inflammation had not been controlled by steroids and several standard anti-rheumatic drugs, and who had developed infections on that treatment, rituximab was followed by a lasting retreat of the skin and mouth ulcers and allowed the steroids to be reduced.

Other approaches

• Topical insulin — a 2023 report described a man with ulcers that had resisted dressings, topical treatments and hyperbaric oxygen; insulin applied to the ulcers as an add-on was followed by clinical improvement.
• Bone marrow (hematopoietic stem cell) transplantation — a 2012 Italian report described an 8-year-old girl with a life-threatening course who received stem cells from her matched brother. After the transplant her red-cell prolidase rose to a carrier-like level and the fragments in her urine fell. She died on day 92 after transplant of an invasive fungal infection. The authors described it as the first evidence that transplant can reverse some of the biochemical features, and stressed that the decision has to be weighed against each patient's illness.
• Enzyme replacement remains experimental; the 2006 recombinant-enzyme work was a step toward it in the laboratory, not a treatment in people.

GeneReviews describes wound care by a specialist for the skin ulcers and standard treatment for each of the other problems as they appear.

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What Is Still Not Known

• How common it is. The 2021 systematic review found 161 published patients in 132 articles. Because some people with two faulty copies have no symptoms, as the 1979 family showed, the count of diagnosed patients may not reflect how many people carry the disorder.
• Why the same gene fault behaves so differently. Brothers and sisters with identical gene changes can range from no symptoms at all to severe ulcers and autoimmune disease.
• Exactly why the ulcers form. Proline shortage in the wound, the toxic effect of the built-up fragments on white blood cells and blood vessels, and immune over-activity have all been proposed; the evidence for each comes from small studies.
• Whether any treatment changes the long-term course. No treatment has been compared against another, or against no treatment, in a controlled trial.
• Whether carriers are affected at all. The studies available, from the 1970s onward, found carriers healthy, with intermediate enzyme activity and near-normal handling of a gelatin load. Whether a single faulty copy matters for wound healing in ordinary life has not been measured in people.

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Key Research Papers

1. Rossignol F, Duarte Moreno MS, Benoist JF, Boehm M, Bourrat E, Cano A, et al. Quantitative analysis of the natural history of prolidase deficiency: description of 17 families and systematic review of published cases. Genetics in Medicine. 2021;23(9):1604-1615. PubMed PMID: 34040193
2. Rossignol F, Wang H, Ferreira C. Prolidase Deficiency. In: GeneReviews. Seattle (WA): University of Washington, Seattle; 1993 (chapter posted 2015, updated 2022). PubMed PMID: 26110198
3. Spodenkiewicz M, Spodenkiewicz M, Cleary M, Massier M, Fitsialos G, Cottin V, et al. Clinical Genetics of Prolidase Deficiency: An Updated Review. Biology (Basel). 2020;9(5):108. PubMed PMID: 32455636
4. Lupi A, Della Torre S, Campari E, Tenni R, Cetta G, Rossi A, Forlino A. Human recombinant prolidase from eukaryotic and prokaryotic sources. Expression, purification, characterization and long-term stability studies. FEBS Journal. 2006;273(23):5466-5478. PubMed PMID: 17081196
5. Endo F, Matsuda I. Molecular basis of prolidase (peptidase D) deficiency. Molecular Biology & Medicine. 1991;8(1):117-127. PubMed PMID: 1943683
6. Boright AP, Scriver CR, Lancaster GA, Choy F. Prolidase deficiency: biochemical classification of alleles. American Journal of Human Genetics. 1989;44(5):731-740. PubMed PMID: 2705457
7. Powell GF, Maniscalco RM. Bound hydroxyproline excretion following gelatin loading in prolidase deficiency. Metabolism. 1976;25(5):503-508. PubMed PMID: 772363
8. Isemura M, Hanyu T, Gejyo F, Nakazawa R, Igarashi R, Matsuo S, et al. Prolidase deficiency with imidodipeptiduria. A familial case with and without clinical symptoms. Clinica Chimica Acta. 1979;93(3):401-407. PubMed PMID: 445856
9. Wang H, Kurien BT, Lundgren D, Patel NC, Kaufman KM, Miller DL, et al. A nonsense mutation of PEPD in four Amish children with prolidase deficiency. American Journal of Medical Genetics Part A. 2006;140(6):580-585. PubMed PMID: 16470701
10. Butbul Aviel Y, Mandel H, Avitan Hersh E, Bergman R, Adiv OE, Luder A, Brik R. Prolidase deficiency associated with systemic lupus erythematosus (SLE): single site experience and literature review. Pediatric Rheumatology Online Journal. 2012;10(1):18. PubMed PMID: 22726576
11. Hodgson R, Crockford TL, Bhandari A, Kepple JD, Back J, Cawthorne E, et al. Prolidase Deficiency Causes Spontaneous T Cell Activation and Lupus-like Autoimmunity. Journal of Immunology. 2023;210(5):547-557. PubMed PMID: 36637239
12. Alrumayyan N, Slauenwhite D, McAlpine SM, Roberts S, Issekutz TB, Huber AM, et al. Prolidase deficiency, a rare inborn error of immunity, clinical phenotypes, immunological features, and proposed treatments in twins. Allergy, Asthma, and Clinical Immunology. 2022;18(1):17. PubMed PMID: 35197125
13. Yasuda K, Ogata K, Kariya K, Kodama H, Zhang J, Sugahara K, et al. Corticosteroid treatment of prolidase deficiency skin lesions by inhibiting iminodipeptide-primed neutrophil superoxide generation. British Journal of Dermatology. 1999;141(5):846-851. PubMed PMID: 10583165
14. Ogata A, Tanaka S, Tomoda T, Murayama E, Endo F, Kikuchi I. Autosomal recessive prolidase deficiency. Three patients with recalcitrant ulcers. Archives of Dermatology. 1981;117(11):689-697. PubMed PMID: 7316526
15. Jemec GB, Moe AT. Topical treatment of skin ulcers in prolidase deficiency. Pediatric Dermatology. 1996;13(1):58-60. PubMed PMID: 8919529
16. Dunn R, Dolianitis C. Prolidase deficiency: the use of topical proline for treatment of leg ulcers. Australasian Journal of Dermatology. 2008;49(4):237-238. PubMed PMID: 18855790
17. Myara I, Charpentier C, Wolfrom C, Gautier M, Lemonnier A, Larregue M, et al. In-vitro responses to ascorbate and manganese in fibroblasts from a patient with prolidase deficiency and iminodipeptiduria: cell growth, prolidase activity and collagen metabolism. Journal of Inherited Metabolic Disease. 1983;6(1):27-31. PubMed PMID: 6408304
18. Good AJ, Nielson CB, Schoch JJ. Topical tacrolimus therapy in the management of lower extremity ulcers due to prolidase deficiency. Pediatric Dermatology. 2019;36(6):926-928. PubMed PMID: 31588604
19. Atschekzei F, Fedchenko M, Elsayed A, Dubrowinskaja N, Graalmann T, Ringshausen FC, et al. Rituximab to treat prolidase deficiency due to a novel pathogenic copy number variation in PEPD. RMD Open. 2023;9(4):e003507. PubMed PMID: 38088248
20. Edek YC, Ertugay Aral HN, Adışen E, Aksakal AB. Topical Insulin Application in the Management of Resistant Leg Ulcers in a Patient With Prolidase Deficiency: A Case Report. Cureus. 2023;15(10):e47672. PubMed PMID: 38021973
21. Caselli D, Cimaz R, Besio R, Rossi A, De Lorenzi E, Colombo R, et al. Partial Rescue of Biochemical Parameters After Hematopoietic Stem Cell Transplantation in a Patient with Prolidase Deficiency Due to Two Novel PEPD Mutations. JIMD Reports. 2012;3:71-77. PubMed PMID: 23430876

PubMed Topic Searches

1. Prolidase deficiency
2. Prolidase deficiency and leg ulcers
3. Prolidase deficiency and lupus
4. Prolidase deficiency and topical proline
5. PEPD gene and prolidase

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Connections

• Dermatology — the skin-disease section this page belongs to
• Manganese and Wound Healing — the enzyme's manganese dependence and collagen recycling
• Manganese — the trace mineral prolidase needs to work
• Proline for Wound Healing — the amino acid the enzyme recycles
• Glycine — the partner in the topical ointments
• Collagen — the protein whose breakdown stalls
• Lupus — the autoimmune disease linked with prolidase deficiency
• Pyoderma Gangrenosum — another cause of hard-to-heal ulcers
• Livedoid Vasculopathy — painful lower-leg ulcers from a different cause
• Varicose Veins — the most common cause of leg ulcers
• Genetics — other inherited disorders on this site

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