Prolidase deficiency: a patient without hydroxyproline-containing iminodipeptides in urine

Further Clinical Delineation of Prolidase Deficiency Associated with c.1103T>G Variant

Introduction

Prolidase deficiency is a rare multisystemic disease associated with collagen metabolism. Clinical manifestations and age of onset are highly variable. Prolidase deficiency is caused by homozygous variants in the PEPD gene. In this report, three siblings with c.1103T>G (L368R) variant in the PEPD gene are presented. They had features not described in the literature and marked intrafamilial clinical heterogeneity. This is the first family of Syrian ancestral origin with prolidase deficiency.

Case Presentation

We performed whole-exome sequencing for the index case, and detected a homozygous c.1103T>G variant, in the PEPD gene. All family members were then screened for the same variant by Sanger sequencing analysis. Two siblings were found to be homozygous, and one of them had not yet developed clinical symptoms.

Conclusion

Our data expand the clinical spectrum of prolidase deficiency. It also improves our knowledge of phenotype and genotype relationships of prolidase deficiency patients.

Quantitative analysis of the natural history of prolidase deficiency: description of 17 families and systematic review of published cases

PURPOSE

Prolidase deficiency is a rare inborn error of metabolism causing ulcers and other skin disorders, splenomegaly, developmental delay, and recurrent infections. Most of the literature is constituted of isolated case reports. We aim to provide a quantitative description of the natural history of the condition by describing 19 affected individuals and reviewing the literature.

METHODS

Nineteen patients were phenotyped per local institutional procedures. A systematic review following PRISMA criteria identified 132 articles describing 161 patients. Main outcome analyses were performed for manifestation frequency, diagnostic delay, overall survival, symptom-free survival, and ulcer-free survival.

RESULTS

Our cohort presented a wide variability of severity. Autoimmune disorders were found in 6/19, including Crohn disease, systemic lupus erythematosus, and arthritis. Another immune finding was hemophagocytic lymphohistiocytosis (HLH). Half of published patients were symptomatic by age 4 and had a delayed diagnosis (mean delay 11.6 years). Ulcers were present initially in only 30% of cases, with a median age of onset at 12 years old.

CONCLUSION

Prolidase deficiency has a broad range of manifestations. Symptoms at onset may be nonspecific, likely contributing to the diagnostic delay. Testing for this disorder should be considered in any child with unexplained autoimmunity, lower extremity ulcers, splenomegaly, or HLH.

Spurious Elevation of Multiple Urine Amino Acids by Ion-Exchange Chromatography in Patients with Prolidase Deficiency

The enzyme prolidase cleaves dipeptides where the C-terminal amino acid corresponds to proline or hydroxyproline. As a consequence, a deficiency of this enzyme leads to accumulation of these dipeptides, which correspondingly are found to be elevated in urine. In fact, the absence of dipeptiduria is sufficient to rule out a diagnosis of prolidase deficiency. However, given the fact that these dipeptides elute at the same position as more common amino acids, the analyzer's software will instead call an elevation of these corresponding amino acids. Thus, an elevation of glycylproline, aspartylproline, glutamylproline, threonylproline and serylproline, valylproline, leucylproline, isoleucylproline, alanylproline, phenylalanylproline, and lysylproline will instead be interpreted as an elevation of leucine, citrulline, methionine, isoleucine, beta-aminoisobutyric acid, gamma-aminobutyric acid, ethanolamine, tyrosine, histidine, and anserine/carnosine, respectively. This particular profile of elevated amino acids, however, can easily be overlooked. We hope that the recognition of this characteristic pattern of falsely elevated urinary amino acids will aid in the recognition of prolidase deficiency.

Prolidase deficiency diagnosed by 1H NMR spectroscopy of urine

Three urine samples from two prolidase-deficient patients were analysed using 1H NMR spectroscopy. One-dimensional 1H NMR spectra showed a characteristic pattern of overlapping resonances of the proline and hydroxyproline protons of the imidodipeptides. The model compounds Ala-Pro, Gly-Pro, Phe-Pro, Leu-Pro, Val-Pro, Gly-Hyp and Pro-Hyp were measured as well. The non-proline resonances of Val-Pro, Ala-Pro and Gly-Pro could be assigned in the urine spectra. These resonances could then be used for quantification of the corresponding imidodipeptids. The presence of Leu-Pro in the patients' urine was demonstrated by the results of COSY experiments. However, this imidodipeptide could not be quantified owing to overlap of the resonaces in the one-dimensional 1H NMR spectrum of the patients' urine. Phe-Pro, Pro-Hyp and Gly-Hyp could not be assigned in the spectrum of the patient's urine. The characteristic resonances in the urine from a prolidase-deficient patient, i.e. Ala-Pro, Val-Pro, Gly-Pro, and resonances of the (hydroxy)proline part of the imidodipeptides can be used to diagnose this disease.

Chronic leg ulcerations resembling vasculitis in two siblings with prolidase deficiency

Two cases of prolidase deficiency in two siblings are presented. The patients complained of the typical clinical symptoms of the disease, including chronic leg ulcerations resembling vasculitis. They were mentally retarded, had typical facial characteristics, splenomegaly, and haematologic anomalies. Biochemical and morphological investigations confirmed the diagnosis. In these cases, alterations of the peripheral nervous system and decreased IgA levels were demonstrated for the first time.

Peroxisomal diseases

The peroxisomal diseases, which are rare inborn metabolic errors, often have serious effects on the well being of the individual and many of them are fatal at an early age. The Zellweger cerebro-hepato-renal syndrome represents a group consisting of diseases with a generalized loss of peroxisomal functions and is considered as a prototype for peroxisomal dysfunction. The largest group includes those diseases where only a single peroxisomal function is impaired. The most common peroxisomal disease, x-linked adrenoleukodystrophy (ADL), belongs to this group, and neurological symptoms dominate among the patients. The primary diagnosis is usually based on clinical findings and measurement of accumulated or depleted metabolites in the body (e.g. very long chain fatty acids, bile acid intermediates or plasmalogens). Some progress has been made in treating of the peroxisomal diseases. Many patients with x-linked ALD have benefitted from the supplementation of the diet with long chain monounsaturated fatty acids like erucic acid or oleic acid with the simultaneous restriction of very long chain fatty acids. Docosahexenoate (C22:1) has also shown promising results in some studies.