Long-term clinical outcome, therapy and mild mitochondrial dysfunction in hyperprolinemia

Although hyperprolinemia type-II has a discriminative metabolic phenotype and is frequently associated with neurological system involvement, the casual relation between the metabolic abnormalities and the clinical features, except for those of the secondary B6 deficiency, has been frequently debated. In order to evaluate disease frequency and the neuro-metabolic outcome we searched our laboratory database between 1992 and 2010, including 20,991 urinary organic acid profiles. From these individuals 16,720 parallel blood samples were available, and were investigated by serum amino acid analysis. We also evaluated the clinical, neurological, psychological features, laboratory data and vitamin levels and therapeutic effect in metabolically confirmed hyperprolinemia. Due to the mitochondrial localization of both ALDH4A1 and PRODH mitochondrial enzyme complex activity was evaluated and oxygen consumption was measured to assess ATP production in patient-fibroblasts. The Mitochondrial Disease Score was used to evaluate clinical mitochondrial dysfunction. The child behavior checklist was used to screen for psychopathology. We found four patients with increased urinary P5C diagnosed with hyperprolinemia type II, and only one patient had hyperprolinemia type I. All children with hyperprolinemia type II had low normal B6 concentration, and three of the patients had biochemical markers suggesting mitochondrial dysfunction. Mitochondrial dysfunction was confirmed in a muscle biopsy in one case. Intellectual disability was found in two adolescent patients. All patients showed seizures and significant behavioral problems, including anxiety and hallucinations. The clinical course was non-progressive and independent from the B6 concentration and B6 therapy. Hyperprolinemia is a rare inborn error. Individuals with hyperprolinemia should be monitored closely due to their frequent behavioral problems.

Identification of PRODH mutations in Korean neonates with type I hyperprolinemia

BACKGROUND

Hyperprolinemia is a rare inherited metabolic disorder characterized by a high proline level in blood and/or urine and various neuropsychiatric symptoms. Type I hyperprolinemia is caused by a proline oxidase deficiency, which is encoded by the PRODH gene on chromosome 22q11. Herein, we present a study of Korean patients with type I hyperprolinemia who were diagnosed during newborn screening by tandem mass spectrometry and confirmed by molecular analysis.

METHODS

Four neonates were referred to our hospital for workup of high proline levels in newborn screening test. We analyzed the biochemical findings and the PRODH gene was amplified by long-range PCR to confirm molecular genetic abnormalities.

RESULTS

All patients had high plasma proline levels, ranging from 742 to 1192 μmol/L (reference range, 77.4 - 244.6 μmol/L). In molecular analysis, 4 disease-associated mutant alleles were identified: c.1414G>A (p.A472T), c.1279G>A (p.V427M), c.1357C>T (p.R453C) and c.1562A>G (p.Q521R). All mutations were missense and c.1279G>A included the majority of mutant alleles. No relationships between type of mutation and clinical outcomes were observed.

CONCLUSION

We found that distinct molecular alterations of the PRODH gene result in abnormal proline levels. Newborn screening and molecular analysis are necessary to identify patients before clinical expression of metabolic disease.

Behavioral and neurochemical effects of proline

Proline is an amino acid with an essential role for primary metabolism and physiologic functions. Hyperprolinemia results from the deficiency of specific enzymes for proline catabolism, leading to tissue accumulation of this amino acid. Hyperprolinemic patients can present neurological symptoms and brain abnormalities, whose aetiopathogenesis is poorly understood. This review addresses some of the findings obtained, mainly from animal studies, indicating that high proline levels may be associated to neuropathophysiology of some disorders. In this context, it has been suggested that energy metabolism deficit, Na(+),K(+)-ATPase, kinase creatine, oxidative stress, excitotoxicity, lipid content, as well as purinergic and cholinergic systems are involved in the effect of proline on brain damage and spatial memory deficit. The discussion focuses on the relatively low antioxidant defenses of the brain and the vulnerability of neural tissue to reactive species. This offers new perspectives for potential therapeutic strategies for this condition, which may include the early use of appropriate antioxidants as a novel adjuvant therapy, besides the usual treatment based on special diets poor in proline.

Physical exercise reverses cognitive impairment in rats subjected to experimental hyperprolinemia

This study investigated whether physical exercise would reverse proline-induced performance deficits in water maze tasks, as well as its effects on brain-derived neurotrophic factor (BDNF) immunocontent and brain acetylcholinesterase (AChE) activity in Wistar rats. Proline administration followed partial time (6th-29th day of life) or full time (6th-60th day of life) protocols. Treadmill exercise was performed from 30th to 60th day of life, when behavioral testing was started. After that, animals were sacrificed for BDNF and AChE determination. Results show that proline impairs cognitive performance, decreases BDNF in cerebral cortex and hippocampus and increases AChE activity in hippocampus. All reported effects were prevented by exercise. These results suggest that cognitive, spatial learning/memory, deficits caused by hyperprolinemia may be associated, at least in part, to the decrease in BDNF levels and to the increase in AChE activity, as well as support the role of physical exercise as a potential neuroprotective strategy.

Role of antioxidants on Na(+),K (+)-ATPase activity and gene expression in cerebral cortex of hyperprolinemic rats

Considering that Na(+),K(+)-ATPase is an embedded-membrane enzyme and that experimental chronic hyperprolinemia decreases the activity of this enzyme in brain synaptic plasma membranes, the present study investigated the effect of chronic proline administration on thiobarbituric acid-reactive substances, as well as the influence of antioxidant vitamins E plus C on the effects mediated by proline on Na(+),K(+)-ATPase activity in cerebral cortex of rats. The expression of Na(+),K(+)-ATPase catalytic subunits was also evaluated. Results showed that proline increased thiobarbituric acid-reactive substances, suggesting an increase of lipid peroxidation. Furthermore, concomitant administration of vitamins E plus C significantly prevented the increase of lipid peroxidation, as well as the inhibition of Na(+),K(+)-ATPase activity caused by proline. We did not observe any change in levels of Na(+),K(+)-ATPase mRNA transcripts after chronic exposure to proline and vitamins E plus C. These findings provide insights into the mechanisms through which proline exerts its effects on brain function and suggest that treatment with antioxidants may be beneficial to treat neurological dysfunctions present in hyperprolinemic patients.

Inborn errors of proline metabolism

l-Proline concentration is primarily related to the balance of enzymatic activities of proline dehydrogenase [proline oxidase (POX)] and Delta-1-pyrroline-5-carboxylate (P5C) reductase. As a result, P5C plays a pivotal role in maintaining the concentration of proline in body fluids and inborn errors of P5C metabolism lead to disturbance of proline metabolism. Several inborn errors of proline metabolism have been described. Hyperprolinemia type I (HPI) is a result of a deficiency in POX. The POX gene (PRODH) is located on chromosome 22 (22q11.2) and this region is deleted in velo-cardio-facial syndrome, a congenital malformation syndrome. In addition, this gene locus is related to susceptibility to schizophrenia. The other type of hyperprolinemia is HPII. It is caused by a deficiency in P5C dehydrogenase activity. Hypoprolinemia, on the other hand, is found in the recently described deficiency of P5C synthetase. This enzyme defect leads to hyperammonemia associated with hypoornithinemia, hypocitrullinemia, and hypoargininemia other than hypoprolinemia. Hyperhydroxyprolinemia is an autosomal recessive inheritance disorder caused by the deficiency of hydroxyproline oxidase. There are no symptoms and it is believed to be a benign metabolic disorder. The deficiency of ornithine aminotransferase causes transient hyperammonemia during early infancy due to deficiency of ornithine in the urea cycle. In later life, gyrate atrophy of the retina occurs due to hyperornithinemia, a paradoxical phenomenon. Finally, prolidase deficiency is a rare autosomal recessive hereditary disease. Prolidase catalyzes hydrolysis of dipeptide or oligopeptide with a C-terminal proline or hydroxyproline and its deficiency can cause mental retardation and severe skin ulcers.

Early neurological phenotype in 4 children with biallelic PRODH mutations

Hyperprolinemia type I (HPI) results from a deficiency of proline oxidase (POX), involved in the first step in the conversion of proline to glutamate. Diverse phenotypes were described in patients with HPI, prior to the identification of the POX gene (PRODH): whereas various patients were asymptomatic, others had neurological and extraneurological defects. The PRODH gene is located in the region deleted in velocardiofacial syndrome (VCFS). Heterozygous and homozygous mutations have been identified in patients with variable hyperprolinemia and various features (patients with schizophrenia, chromosome 22q11 microdeletions and/or neurological defects). A functional study has divided the PRODH missense mutations into three groups: those leading to mild, moderate, or severe reduction of POX activity. In this study, we report four unrelated children with HPI and a homogeneous severe neurological phenotype. We identified biallelic abnormalities in PRODH in these patients that led to severe reduction of POX activity. These included missense and non-sense mutations, deletions of PRODH and a 22q11 microdeletion. Four other children have been reported with severe biallelic PRODH mutations. The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy. Their values of hyperprolinemia ranged from 400 to 2200 micromol/L. Patients with biallelic PRODH alterations resulting in severely impaired POX activity had an early onset and severe neurological features. Thus, children with this phenotype and those with a microdeletion in chromosome 22q11, especially those with mental retardation and autistic features, should be tested for hyperprolinemia. Hyperprolinemic patients should be screened for PRODH mutations.

Functional consequences of PRODH missense mutations

PRODH maps to 22q11 in the region deleted in the velocardiofacial syndrome/DiGeorge syndrome (VCFS/DGS) and encodes proline oxidase (POX), a mitochondrial inner-membrane enzyme that catalyzes the first step in the proline degradation pathway. At least 16 PRODH missense mutations have been identified in studies of type I hyperprolinemia (HPI) and schizophrenia, 10 of which are present at polymorphic frequencies. The functional consequences of these missense mutations have been inferred by evolutionary conservation, but none have been tested directly. Here, we report the effects of these mutations on POX activity. We find that four alleles (R185Q, L289M, A455S, and A472T) result in mild (<30%), six (Q19P, A167V, R185W, D426N, V427M, and R431H) in moderate (30%-70%), and five (P406L, L441P, R453C, T466M, and Q521E) in severe (>70%) reduction in POX activity, whereas one (Q521R) increases POX activity. The POX encoded by one severe allele (T466M) shows in vitro responsiveness to high cofactor (flavin adenine dinucleotide) concentrations. Although there is limited information on plasma proline levels in individuals of known PRODH genotype, extant data suggest that severe hyperprolinemia (>800 microM) occurs in individuals with large deletions and/or PRODH missense mutations with the most-severe effect on function (L441P and R453C), whereas modest hyperprolinemia (300-500 microM) is associated with PRODH alleles with a moderate reduction in activity. Interestingly, three of the four alleles associated with or found in schizophrenia (V427M, L441P, and R453C) resulted in severe reduction of POX activity and hyperprolinemia. These observations plus the high degree of polymorphism at the PRODH locus are consistent with the hypothesis that reduction in POX function is a risk factor for schizophrenia.

Is hyperprolinemia type I actually a benign trait? Report of a case with severe neurologic involvement and vigabatrin intolerance

Hyperprolinemia type I is a deficiency of proline oxidase (McKusick 23950), leading to hyperprolinemia and iminoglycinuria, usually with renal involvement. Hyperprolinemia type I is considered a benign trait. We reported a case of hyperprolinemia type I with a severe neurologic disorder and without renal involvement. The patient had marked psychomotor delay and right hemiparesis. Epilepsy was characterized by status epilepticus or a cluster of seizures. Laboratory findings revealed elevated levels of proline in the serum, urine, and cerebrospinal fluid without delta1-pyrroline 5-carboxylate dehydrogenase in the plasma or urine. Fluorescence in situ hybridization excluded a chromosome 22q11 deletion. Vigabatrin inhibits ornithine transaminase. Thus, vigabatrin could lead to a depletion of the normal pool of pyrroline 5-carboxylate dehydrogenase and could aggravate the clinical condition of the child. In this study, vigabatrin was discontinued. In the following months, the patient had marked psychomotor improvement, without modification of the epilepsy. We suggest that vigabatrin should be avoided in hyperprolinemia type I.

Type I hyperprolinemia

Type I hyperprolinemia is an autosomal recessive disorder characterized by increased plasma and urine proline concentrations due to a deficiency of the enzyme, proline oxidase. This rare inborn error of proline metabolism is generally believed to be a benign condition although many associated clinical abnormalities have been reported. We report two siblings with Type I hyperprolinemia who presented with recurrent seizures. They had elevated plasma proline levels with massive prolinuria without an increased urinary excretion of delta 1-pyrolline-carboxylic acid.

Clinical, biochemical and enzymatic studies in type I hyperprolinemia associated with chromosomal abnormality

A severe mentally retarded infant with type I hyperprolinemia associated with chromosomal abnormality is reported. The patient had a characteristic facial appearance of hyperprolinemia and suffered from convulsions after the age of 10 months. The child developed severe mental and motor retardation. The karyotype of the patient revealed partial duplication of the short arm in chromosome 10 using G banding techniques. The patient and her mother showed a fasting hyperprolinemia and an abnormal clearance curve after the proline load in the serum. The proline oxidase activities of the liver tissues obtained by biopsy in the patient was about 9% of those of controls. Kinetic studies and mixed experiments of the enzyme were with normal limits. Restriction of dietary proline at the age of 12 months revealed a prompt fall of the plasma levels of proline to the normal range, and a low proline diet was continued until the present time. During the period of dietary treatment, growth was satisfactory, but her mental development did not improve. From the developmental patterns of proline oxidase activities postnataldy, we speculated that restriction of dietary proline intake should be relieved with age.

Hyperprolinaemia and gyrate atrophy of the choroid and retina in members of the same family

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