Neurologic Status of Patients with Purine Nucleoside Phosphorylase Deficiency Before and After Hematopoetic Stem Cell Transplantation.

BACKGROUND: Purine nucleoside phosphorylase (PNP) deficiency is a rare autosomal recessive combined immunodeficiency. The phenotype is profound T cell deficiency with variable B and NK cell functions and results in recurrent and persistent infections that typically begin in the first year of life. Neurologic findings occur in approximately two-thirds of patients. The mechanism of neurologic abnormalities is unclear. Hematopoietic stem cell transplantation (HSCT) is the only curative treatment for PNP deficiency. METHODS: We report here six patients from five unrelated families with PNP deficiency treated in two centers in Turkey. We evaluated the neurological status of patients and compared to post-transplantation period if available. Then, we performed PubMed, Google Scholar, and Researchgate searches using the terms "PNP" and "hematopoietic stem cell transplantation" to find all reported cases of PNP transplantation and compared to our cohort. RESULTS: Six patients were treated in two centers in Turkey. One patient died from post-transplant complications. The other four patients underwent successful HSCT with good immune reconstitution after transplantation (follow-up 21-48 months) and good neurological outcomes. The other patient with a new mutation is still waiting for a matching HLA donor. DISCUSSION: In PNP deficiency, clinical manifestations are variable, and this disease should be considered in the presence of many different clinical findings. Despite the comorbidities that occurred before transplantation, HSCT currently appears to be the only treatment option for this disease. HSCT not only cures immunologic disorders, but probably also improves or at least stabilizes the neurologic status of patients.

Partial Purine Nucleoside Phosphorylase Deficiency Helps Determine Minimal Activity Required for Immune and Neurological Development.

Introduction: Complete or near complete absence of the purine nucleoside phosphorylase (PNP) enzyme causes a profound T cell immunodeficiency and neurological abnormalities that are often lethal in infancy and early childhood. We hypothesized that patients with partial PNP deficiency, characterized by a late and mild phenotype due to residual PNP enzyme, would provide important information about the minimal PNP activity needed for normal development. Methods: Three siblings with a homozygous PNP gene mutation (c.769C>G, p.His257Asp) resulting in partial PNP deficiency were investigated. PNP activity was semi-quantitively assayed by the conversion of [14C]inosine in hemolysates, mononuclear cells, and lymphoblastoid B cells. PNP protein expression was determined by Western Blotting in lymphoblastoid B cells. DNA repair was quantified by measuring viability of lymphoblastoid B cells following ionizing irradiation. Results: A 21-year-old female was referred for recurrent sino-pulmonary infections while her older male siblings, aged 25- and 28- years, did not suffer from significant infections. Two of the siblings had moderately reduced numbers of T, B, and NK cells, while the other had near normal lymphocyte subset numbers. T cell proliferations were normal in the two siblings tested. Hypogammaglobulinemia was noted in two siblings, including one that required immunoglobulin replacement. All siblings had typical (normal) neurological development. PNP activity in various cells from two patients were 8-11% of the normal level. All siblings had normal blood uric acid and increased PNP substrates in the urine. PNP protein expression in cells from the two patients examined was similar to that observed in cells from healthy controls. The survival of lymphoblastoid B cells from 2 partial PNP-deficient patients after irradiation was similar to that of PNP-proficient cells and markedly higher than the survival of cells from a patient with absent PNP activity or a patient with ataxia telangiectasia. Conclusions: Patients with partial PNP deficiency can present in the third decade of life with mild-moderate immune abnormalities and typical development. Near-normal immunity might be achieved with relatively low PNP activity.

A Case with Purine Nucleoside Phosphorylase Deficiency Suffering from Late-Onset Systemic Lupus Erythematosus and Lymphoma.

BACKGROUND: Purine nucleoside phosphorylase (PNP) deficiency accounts for about 4% of severe combined immunodeficiency diseases. PNP deficiency is a variable disease with recurrent infections and neurodevelopmental delay. Autoimmunity and malignancy can still occur in one-third of patients. METHODS: Case report. CASE PRESENTATION: An 8-year-old Saudi female who was apparently healthy presented at the age of 7 years with confirmed systemic lupus erythematosus (SLE) and lupus nephritis that were poorly controlled with conventional therapy. She also had frequent sinopulmonary and varicella infections. Preliminary immunological workup showed severe lymphopenia and depressed lymphocyte proliferation assay. The uric acid was within normal levels at 179 µmol/L (normal range, 150 to 350 µmol/L) 6 weeks after blood transfusion. Genetic study revealed a homozygous missense mutation c.265G>A in the PNP gene, resulting in a substitution of glutamic acid to lysine at amino acid 89 of the encoded protein (E89K). The PNP serum level was 798 nmol/h/mg (normal level 1354 ± 561 nmol/h/mg) 6 weeks after blood transfusion. Hematopoietic stem cell transplantation (HSCT) was planned from a matched unrelated donor; however, she developed an EBV and varicella meningoencephalitis. Atypical malignant cells suggestive of lymphoma were discovered, likely induced by EBV, and suspicious lesions were shown on brain MRI and PET scan. Unfortunately, she passed away before HSCT due to multiorgan failure. CONCLUSION: This report emphasizes the challenges in recognizing PNP deficiency in a patient suffering from SLE.

A successful unrelated peripheral blood stem cell transplantation with reduced intensity-conditioning regimen in a patient with late-onset purine nucleoside phosphorylase deficiency.

PNP deficiency is a rare combined immunodeficiency with autosomal recessive mode of inheritance. The immunodeficiency is progressive with normal immune functions at birth, but then, T-cell deficiency with variable B-cell functions usually presents by the age of two yr. The only curative treatment for PNP deficiency is hematopoietic stem cell transplantation. Here, we present a 13-yr-old girl with late-onset PNP deficiency. Despite many complications of infections, she was successfully transplanted with a reduced intensity-conditioning regimen from an HLA-identical unrelated donor.

Inborn errors of pyrimidine metabolism: clinical update and therapy.

Inborn errors involving enzymes essential for pyrimidine nucleotide metabolism have provided new insights into their fundamental physiological roles as vital constituents of nucleic acids as well as substrates of lipid and carbohydrate metabolism and in oxidative phosphorylation. Genetic aberrations of pyrimidine pathways lead to diverse clinical manifestations including neurological, immunological, haematological, renal impairments, adverse reactions to analogue therapy and association with malignancies. Maintenance of cellular nucleotides depends on the three aspects of metabolism of pyrimidines: de novo synthesis, catabolism and recycling of these metabolites. Of the ten recognised disorders of pyrimidine metabolism treatment is currently restricted to only two disorders: hereditary orotic aciduria (oral uridine therapy) and mitochondrial neurogastrointestinal encephalomyopathy (MNGIE; allogeneic hematopoetic stem cell transplant and enzyme replacement). The ubiquitous role that pyrimidine metabolism plays in human life highlights the importance of improving diagnostic evaluation in suggestive clinical settings, which will contribute to the elucidation of new defects, future development of novel drugs and therapeutic strategies. Limited awareness of the expanding phenotypic spectrum, with relatively recent descriptions of newer disorders, compounded by considerable genetic heterogeneity has often contributed to the delays in the diagnosis of this group of disorders. The lack of an easily recognisable, easily measurable end product, akin to uric acid in purine metabolism, has contributed to the under-recognition of these disorders.This review describes the currently known inborn errors of pyrimidine metabolism, their variable phenotypic presentations, established diagnostic methodology and recognised treatment options.

Inborn errors of purine metabolism: clinical update and therapies.

Inborn errors of purine metabolism exhibit broad neurological, immunological, haematological and renal manifestations. Limited awareness of the phenotypic spectrum, the recent descriptions of newer disorders and considerable genetic heterogeneity, have contributed to long diagnostic odysseys for affected individuals. These enzymes are widely but not ubiquitously distributed in human tissues and are crucial for synthesis of essential nucleotides, such as ATP, which form the basis of DNA and RNA, oxidative phosphorylation, signal transduction and a range of molecular synthetic processes. Depletion of nucleotides or accumulation of toxic intermediates contributes to the pathogenesis of these disorders. Maintenance of cellular nucleotides depends on the three aspects of metabolism of purines (and related pyrimidines): de novo synthesis, catabolism and recycling of these metabolites. At present, treatments for the clinically significant defects of the purine pathway are restricted: purine 5'-nucleotidase deficiency with uridine; familial juvenile hyperuricaemic nephropathy (FJHN), adenine phosphoribosyl transferase (APRT) deficiency, hypoxanthine phosphoribosyl transferase (HPRT) deficiency and phosphoribosyl-pyrophosphate synthetase superactivity (PRPS) with allopurinol; adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) deficiencies have been treated by bone marrow transplantation (BMT), and ADA deficiency with enzyme replacement with polyethylene glycol (PEG)-ADA, or erythrocyte-encapsulated ADA; myeloadenylate deaminase (MADA) and adenylosuccinate lyase (ADSL) deficiencies have had trials of oral ribose; PRPS, HPRT and adenosine kinase (ADK) deficiencies with S-adenosylmethionine; and molybdenum cofactor deficiency of complementation group A (MOCODA) with cyclic pyranopterin monophosphate (cPMP). In this review we describe the known inborn errors of purine metabolism, their phenotypic presentations, established diagnostic methodology and recognised treatment options.

An unconditioned bone marrow transplantation in a child with purine nucleoside phosphorylase deficiency and its unique complication.

Purine nucleoside phosphorylase deficiency is a rare immunodeficiency syndrome characterized by recurrent infections, neurological dysfunction, and autoimmunity. Early diagnosis and hematopoietic stem cell transplantation may reverse the dismal prognosis in PNP deficiency. This report presents a new PNP deficiency case successfully transplanted without a conditioning regimen from an HLA-identical family donor, who developed a complication of disseminated BCG infection.

Pyrimidine pathways in health and disease.

Genetic defects involving enzymes essential for pyrimidine nucleotide metabolism have provided new insights into the vital physiological functions of these molecules in addition to nucleic acid synthesis. Such aberrations disrupt the haematological, nervous or mitochondrial systems and can cause adverse reactions to analogue therapy. Regulation of pyrimidine pathways is also known to be disrupted in malignancies. Nine genetic defects have now been identified but only one is currently treatable. Diagnosis is aided by the accumulation of specific metabolites. Recently, progress has been made in understanding the molecular mechanisms underlying inborn errors of pyrimidine metabolism, together with the key clinical issues and the implications for the future development of novel drugs and therapeutic strategies.

Persistence and expression of the adenosine deaminase gene for 12 years and immune reaction to gene transfer components: long-term results of the first clinical gene therapy trial.

The first human gene therapy experiment begun in September 1990 used a retroviral vector containing the human adenosine deaminase (ADA) cDNA to transduce mature peripheral blood lymphocytes from patients with ADA deficiency, an inherited disorder of immunity. Two patients who had been treated with intramuscular injections of pegylated bovine ADA (PEG-ADA) for 2 to 4 years were enrolled in this trial and each received a total of approximately 10(11) cells in 11 or 12 infusions over a period of about 2 years. No adverse events were observed. During and after treatment, the patients continued to receive PEG-ADA, although at a reduced dose. Ten years after the last cell infusion, approximately 20% of the first patient's lymphocytes still carry and express the retroviral gene, indicating that the effects of gene transfer can be remarkably long lasting. On the contrary, the persistence of gene-marked cells is very low (< 0.1%), and no expression of the transgene is detectable in lymphocytes from the second patient who developed persisting antibodies to components of the gene transfer system. Data collected from these original patients have provided novel information about the longevity of T lymphocytes in humans and persistence of gene expression in vivo from vectors driven by the Moloney murine leukemia virus long-terminal repeat (LTR) promoter. This long-term follow-up has also provided unique evidence supporting the safety of retroviral-mediated gene transfer and illustrates clear examples of both the potential and the pitfalls of gene therapy in humans.

Persistent developmental delay despite successful bone marrow transplantation for purine nucleoside phosphorylase deficiency.

A 10-month-old girl with a history of recurrent candidiasis, developmental delay, and a fulminant varicella infection is described. The diagnosis of purine nucleoside phosphorylase (PNP) deficiency was suggested by a reduced level of serum uric acid and confirmed by measurement of PNP activity. A human leukocyte antigen-matched bone marrow transplantation resulted in immune reconstitution, but poor neurodevelopmental progression.

How should we treat tophaceous gout in patients with allopurinol hypersensitivity?

We studied purine metabolism in gouty patients from three categories: primary gout, familial juvenile hyperuricaemic nephropathy (FJHN) and partial HPRT deficiency.

Inborn errors of pyrimidine degradation: clinical, biochemical and molecular aspects.

The pyrimidines, uracil and thymine, are degraded in four steps. The first three steps of pyrimidine catabolism, controlled by enzyme shared by both pathways, result in the production of the neurotransmitter amino acid beta-alanine from uracil and the nonfunctional (R)-(-)-beta-aminoisobutyrate from thymine. The fourth step is controlled by several aminotransferases, which have different affinities for beta-alanine, beta-aminoisobutyrate and GABA. Defects concerning the first three steps all lead to a reduced production of beta-alanine; defects of the transaminases involving the metabolism of beta-alanine and GABA lead to accumulation of these neurotransmitter substances. In addition, other metabolites will accumulate or be reduced depending on the specific enzyme defect. Analysis of the abnormal concentrations of these metabolites in the body fluids is essential for the detection of patients with pyrimidine degradation defects. Clinically these disorders are often overlooked because symptomatology is highly aspecific. The growth in our knowledge concerning inborn errors of pyrimidine degradation has emphasized the importance of the clinical awareness of these defects as a possible cause of neurological disease and a contraindication for treatment of cancer patients with certain pyrimidine analogues. The various defects are discussed and attention is paid to clinical genetic and diagnostic aspects.

[Gene therapy for genetic disorders of purine metabolism].

Anderson proposed three genetic diseases deficient in enzymes involved in purine metabolism as candidate for human gene therapy in 1984. Over the past ten years, marked advances in molecular genetics have brought gene therapy to reality. Gene therapy for ADA deficiency was performedin the United States in 1990 and in Japan in 1995 as the first trial. Basic study for HPRT gene transfer has been proceeding toward gene therapy for HPRT deficiency despite the difficulties in gene transfer into the nervous systems.

Approaches to gene therapy in disorders of purine metabolism.

Model studies with gene transfer technology using retroviral vectors expressing the cloned human genes for adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP), and hypoxanthine guanine phosphoribosyltransferase (HPRT) indicate that these disorders may eventually be treated by the introduction of the normal gene into defective cells. The autologous transplantation of bone marrow infected in vitro with retroviral vectors is the most developed approach at this time. The potential usefulness of this and other approaches for each of these three disorders of purine metabolism are discussed.

Adenosine deaminase and purine nucleoside phosphorylase deficiencies: evaluation of therapeutic interventions in eight patients.

The courses of six patients with adenosine deaminase (ADA) and two with purine nucleoside phosphorylase (PNP) deficiencies were evaluated before and after therapy. The heterogeneity of immunologic and clinical parameters was striking in each enzyme deficiency. In both PNP and ADA deficiency, some patients had very low immunoglobulin levels, while others had normal levels. T-cell function was always low in patients with ADA deficiency. In the two patients with PNP deficiency, contrary to the classical descriptions of this disorder, T-cell function fluctuated with time. Five ADA-deficient patients were treated with irradiated normal red-cell transfusions as a form of enzyme replacement and showed no lasting benefit. Three of the ADA-deficient patients and one of the PNP-deficient patients were given transplants of haploidentical parental bone marrow stem cells without pretransplant immunosuppression. In the PNP-deficient patient, chimerism has not been documented on enzymatic testing. One ADA-deficient patient has demonstrated long-term engraftment with good B- and T-cell function. Haploidentical bone marrow transplantation is currently the preferred therapy for enzyme-deficient patients with absent T-cell function who do not have an HLA-identical donor, as it may result in a lasting reconstitution of immune function. In those patients with unsatisfactory responses to transplantation, however, specific enzyme replacement or gene therapy may be considered in the future.

Gene replacement therapy for inborn errors of purine metabolism.

Effective retroviral vectors carrying the human HPRT and ADA genes have been described. Initial characterization of the retroviral gene transfer system using the HPRT vector allowed the delineation of several parameters important in viral titer, expression, and stability. Using the HPRT and ADA vectors, we have initiated experiments designed to insert these human genes into various tissues of the mouse and have demonstrated expression of both transduced genes in mouse bone marrow cells. Further work with these and other vector constructions is underway in the hope that this technique may allow safe and effective treatment of ADA and HPRT deficiencies, paving the way for treatments of other inborn errors of metabolism through somatic gene replacement therapy.