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

Purine Nucleoside Phosphorylase Deficient Severe Combined Immunodeficiencies: A Case Report and Systematic Review (1975-2022)

Purine nucleoside phosphorylase deficient severe combined immunodeficiency (PNP SCID) is one of the rare autosomal recessive primary immunodeficiency disease, and the data on epidemiology and outcome are limited. We report the successful management of a child with PNP SCID and present a systematic literature review of published case reports, case series, and cohort studies on PNP SCID listed in PubMed, Web of Science, and Scopus from 1975 until March 2022. Forty-one articles were included from the 2432 articles retrieved and included 100 PNP SCID patients worldwide. Most patients presented with recurrent infections, hypogammaglobulinaemia, autoimmune manifestations, and neurological deficits. There were six reported cases of associated malignancies, mainly lymphomas. Twenty-two patients had undergone allogeneic hematopoietic stem cell transplantation with full donor chimerism seen mainly in those receiving matched sibling donors and/or conditioning chemotherapy before the transplant. This research provides a contemporary, comprehensive overview on clinical manifestations, epidemiology, genotype mutations, and transplant outcome of PNP SCID. These data highlight the importance of screening for PNP SCID in cases presented with recurrent infections, hypogammaglobulinaemia, and neurological deficits.

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.

The First Purine Nucleoside Phosphorylase Deficiency Patient Resembling IgA Deficiency and a Review of the Literature

Purine nucleoside phosphorylase (PNP) deficiency is a rare autosomal recessive primary immunodeficiency disorder characterized by decreased numbers of T-cells, variable B-cell abnormalities, decreased amount of serum uric acid and PNP enzyme activity. The affected patients usually present with recurrent infections, neurological dysfunction and autoimmune phenomena. In this study, whole-exome sequencing was used to detect mutation in the case suspected of having primary immunodeficiency. We found a homozygous mutation in PNP gene in a girl who is the third case from the national Iranian registry. She had combined immunodeficiency, autoimmune hemolytic anemia and a history of recurrent infections. She developed no neurological dysfunction. She died at the age of 11 after a severe chicken pox infection. PNP deficiency should be considered in late-onset children with recurrent infections, autoimmune disorders without typical neurologic impairment.

Inborn errors of metabolism underlying primary immunodeficiencies

A number of inborn errors of metabolism (IEM) have been shown to result in predominantly immunologic phenotypes, manifesting in part as inborn errors of immunity. These phenotypes are mostly caused by defects that affect the (i) quality or quantity of essential structural building blocks (e.g., nucleic acids, and amino acids), (ii) cellular energy economy (e.g., glucose metabolism), (iii) post-translational protein modification (e.g., glycosylation) or (iv) mitochondrial function. Presenting as multisystemic defects, they also affect innate or adaptive immunity, or both, and display various types of immune dysregulation. Specific and potentially curative therapies are available for some of these diseases, whereas targeted treatments capable of inducing clinical remission are available for others. We will herein review the pathogenesis, diagnosis, and treatment of primary immunodeficiencies (PIDs) due to underlying metabolic disorders.

Combined immunodeficiency associated with DOCK8 mutations

BACKGROUND

Recurrent sinopulmonary and cutaneous viral infections with elevated serum levels of IgE are features of some variants of combined immunodeficiency. The genetic causes of these variants are unknown.

METHODS

We collected longitudinal clinical data on 11 patients from eight families who had recurrent sinopulmonary and cutaneous viral infections. We performed comparative genomic hybridization arrays and targeted gene sequencing. Variants with predicted loss-of-expression mutations were confirmed by means of a quantitative reverse-transcriptase-polymerase-chain-reaction assay and immunoblotting. We evaluated the number and function of lymphocytes with the use of in vitro assays and flow cytometry.

RESULTS

Patients had recurrent otitis media, sinusitis, and pneumonias; recurrent Staphylococcus aureus skin infections with otitis externa; recurrent, severe herpes simplex virus or herpes zoster infections; extensive and persistent infections with molluscum contagiosum; and human papillomavirus infections. Most patients had severe atopy with anaphylaxis; several had squamous-cell carcinomas, and one had T-cell lymphoma-leukemia. Elevated serum IgE levels, hypereosinophilia, low numbers of T cells and B cells, low serum IgM levels, and variable IgG antibody responses were common. Expansion in vitro of activated CD8 T cells was impaired. Novel homozygous or compound heterozygous deletions and point mutations in the gene encoding the dedicator of cytokinesis 8 protein (DOCK8) led to the absence of DOCK8 protein in lymphocytes.

CONCLUSIONS

Autosomal recessive DOCK8 deficiency is associated with a novel variant of combined immunodeficiency.

TAT-mediated intracellular delivery of purine nucleoside phosphorylase corrects its deficiency in mice

Defects in purine nucleoside phosphorylase (PNP) enzyme activity result in abnormal nucleoside homeostasis, severe T cell immunodeficiency, neurological dysfunction, and early death. Protein transduction domain (PTD) can transfer molecules into cells and may help restore PNP activity in cases of PNP deficiency. However, long-term use of PTD to replace enzymes in animal models or patients has not previously been described. We fused human PNP to the HIV-TAT PTD and found that the fusion with TAT changed the retention and distribution of PNP in PNP-deficient mice. TAT induced rapid intracellular delivery of PNP into tissues, including the brain, prevented urinary excretion of PNP, and protected PNP from neutralizing antibodies, resulting in significant extension of the enzyme's biological activity in vivo. Frequent TAT-PNP injections in PNP-deficient mice corrected the metabolic disorder and immune defects with no apparent toxicity. TAT-PNP remained effective over 24 weeks of treatment, resulting in continued improvement in immune function and extended survival. Our data demonstrate that TAT changes the properties of PNP in vivo and that long-term intracellular delivery of PNP by TAT corrects PNP deficiency in mice. We provide evidence to promote further use of PTD to treat diseases that require repeated intracellular enzyme or protein delivery.

Intracellular delivery of purine nucleoside phosphorylase (PNP) fused to protein transduction domain corrects PNP deficiency in vitro

Purine nucleoside phosphorylase (PNP) is an intracellular enzyme crucial for purine degradation. PNP defects result in metabolic abnormalities and fatal T cell immunodeficiency. Protein transduction domains (PTD) transfer molecules across biological membranes. We hypothesized that fusion of PTD to PNP (PTD-PNP) would be an effective method for treating PNP deficiency. We find that PTD-PNP rapidly enters PNP-deficient lymphocytes and increases intracellular enzyme activity for 96 h. Similar to endogenous PNP, PTD-PNP is predominantly distributed in the cytoplasm. PTD-PNP improve viability and correct abnormal functions of PNP-deficient T lymphocytes including their response to stimulation and IL-2 secretion. Intracellular transduction protects PTD-PNP from antibody neutralization and from elimination, which may also provide significant in vivo therapeutic advantages to PNP. In conclusion, PTD fusion is an attractive method for extended PNP intracellular enzyme replacement therapy for PNP-deficient patients as well as for the intracellular delivery of other proteins.

Purine nucleoside phosphorylase deficiency associated with a dysplastic marrow morphology

Purine nucleoside phosphorylase (PNP) deficiency is an autosomal recessive metabolic disorder characterized by severe combined immunodeficiency and by complex neurologic symptomatology including ataxia, developmental delay, and spasticity. Herein we report severe marrow dysplasia in a patient with PNP deficiency. Drug-related marrow dysfunction was unlikely, and marrow virological studies were negative. A preleukemic myelodysplastic syndrome was also unlikely due to normal marrow CD34+ cells, colony growth in clonogenic assay of marrow mononuclear cells, apoptosis rate, and Fas expression on marrow nucleated cells, as well as morphologic improvement of the marrow dysplasia after normal red blood cell transfusion. The patient's marrow stroma showed hypersensitivity to irradiation and undetectable PNP enzyme activity similar to peripheral lymphocytes. This is the first report of PNP deficiency associated with increased lymphocyte and marrow stromal sensitivity to irradiation. We conclude that marrows from patients with PNP deficiency might have hypersensitivity to irradiation and can develop dysplastic morphology, caused either directly or indirectly by the inherited enzymatic defect.

Severe combined immunodeficiency: otolaryngological presentation and management

In order to increase the awareness of otolaryngologists of severe combined immunodeficiency syndrome (SCIDS) so they may contribute to an earlier diagnosis of this disorder, we performed a retrospective chart review of a multicenter series from 2 children's hospital medical centers. Eighteen cases were identified, and 14 had an otolaryngological presentation. The average age of presentation was 3.3 months, and 72% were males. Most cases were inherited in an X-linked fashion. Five patients had thrush; 4 had recurrent otitis media. Other otolaryngological presentations included cough, mouth ulcers, pharyngitis, mastoiditis, and bilateral neck abscess. The most severe form of immunodeficiency, SCIDS is a rare condition that involves a disorder in both T and B cell functions. The manifestations involving the head and neck include recurrent upper respiratory tract infections, otitis media, thrush, oral ulcers, and abscesses. It is important that SCIDS be considered in any infant with recurrences of these common infections.

Adenosine deaminase deficiency: genotype-phenotype correlations based on expressed activity of 29 mutant alleles

Adenosine deaminase (ADA) deficiency causes lymphopenia and immunodeficiency due to toxic effects of its substrates. Most patients are infants with severe combined immunodeficiency disease (SCID), but others are diagnosed later in childhood (delayed onset) or as adults (late onset); healthy individuals with "partial" ADA deficiency have been identified. More than 50 ADA mutations are known; most patients are heteroallelic, and most alleles are rare. To analyze the relationship of genotype to phenotype, we quantitated the expression of 29 amino acid sequence-altering alleles in the ADA-deleted Escherichia coli strain SO3834. Expressed ADA activity of wild-type and mutant alleles ranged over five orders of magnitude. The 26 disease-associated alleles expressed 0.001%-0.6% of wild-type activity, versus 5%-28% for 3 alleles from "partials." We related these data to the clinical phenotypes and erythrocyte deoxyadenosine nucleotide (dAXP) levels of 52 patients (49 immunodeficient and 3 with partial deficiency) who had 43 genotypes derived from 42 different mutations, including 28 of the expressed alleles. We reduced this complexity to 13 "genotype categories," ranked according to the potential of their constituent alleles to provide ADA activity. Of 31 SCID patients, 28 fell into 3 genotype categories that could express <=0.05% of wild-type ADA activity. Only 2 of 21 patients with delayed, late-onset, or partial phenotypes had one of these "severe" genotypes. Among 37 patients for whom pretreatment metabolic data were available, we found a strong inverse correlation between red-cell dAXP level and total ADA activity expressed by each patient's alleles in SO3834. Our system provides a quantitative framework and ranking system for relating genotype to phenotype.

Adenosine deaminase deficiency and purine nucleoside phosphorylase deficiency in common variable immunodeficiency

The clinical presentations of adenosine deaminase deficiency and purine nucleoside phosphorylase deficiency are widely variable and include clinical and immunologic findings compatible with common variable immunodeficiency. The screening of 44 patients with common variable immunodeficiency failed to identify any individuals with deficiencies of these enzymes.

Human severe combined immunodeficiency: genetic, phenotypic, and functional diversity in one hundred eight infants

OBJECTIVE

To determine the relative frequencies of the different genetic forms of severe combined immunodeficiency (SCID) and whether there are distinctive characteristics of the particular genotypes.

STUDY DESIGN

The demographic, genetic, and immunologic features of 108 infants with SCID who were treated consecutively at Duke University Medical Center were analyzed.

RESULTS

Eighty-nine subjects were boys and 19 were girls; there were 84 white infants, 16 black infants, and 8 Hispanic infants. Forty-nine had X-linked SCID with mutations of common cytokine receptor gamma chain (gamma c), 16 had adenosine deaminase (ADA) deficiency, 8 had Janus kinase 3 (Jak3) deficiency, 21 had unknown autosomal recessive mutations, 1 had reticular dysgenesis, 1 had cartilage hair hypoplasia, and 12 (all boys) had SCID of undetermined type. Deficiency of ADA caused the most profound lymphopenia; gamma c or Jak3 deficiency resulted in the most B cells and fewest natural killer (NK) cells; NK cells and function were highest in autosomal recessive and unknown types of SCID.

CONCLUSIONS

Different SCID genotypes are associated with distinctive lymphocyte characteristics. The presence of NK function in ADA-deficient, autosomal recessive, and unknown type SCIDs, and low NK function in a majority of gamma c and Jak3 SCIDs indicates that some molecular lesions affect T, B, and NK cells (gamma c and Jak3), others primarily T cells (ADA deficiency), and others just T and B cells.

Immunodeficiency as a component of recognizable syndromes

Immunodeficiency occurs in numerous genetic syndromes. While it is the dominant manifestation in primary immunodeficiencies, immune deficits may also be seen in a variety of other recognizable syndromes. Immunodeficiency has been reported in 64 such conditions, adding to the 45 recognized primary immunodeficiencies. These uncommon syndromes with immune defects can present with: (a) growth deficiency (11 syndromes with disproportionate or proportionate short stature), (b) specific organ system dysfunction (18 with gastrointestinal, dermatologic, or neurologic abnormalities), (c) inborn errors of metabolism (13), (d) miscellaneous anomalies (10), or (e) chromosome anomalies (12). In most of the disorders, only some of the affected patients have immune defects. However, in 27 syndromes, immunodeficiency is a constant finding. We briefly review the clinical manifestations of each syndrome and delineate the specific associated immune defects. In most syndromes, the connection between the immune and other defects is unknown. Recognition of these conditions involving both the immune and other organ systems may facilitate accurate diagnosis and management as well as yield information regarding genes critical for the development of the involved systems.

Correction of purine nucleoside phosphorylase deficiency by transplantation of allogeneic bone marrow from a sibling

Deficiency of the purine salvage pathway enzyme purine nucleoside phosphorylase causes a combined immunodeficiency and neurologic abnormalities and is usually fatal in childhood. We report the first successful transplantation of bone marrow from a sibling with identical class II human leukocyte antigens in this condition, demonstrating correction of both lymphocyte metabolic and functional abnormalities.

Stem cells from bone marrow, umbilical cord blood and peripheral blood for clinical application: current status and future application

Bone marrow transplantation (BMT) has progressed rapidly during the past two decades to that of a treatment of choice as a therapeutically effective modality for the treatment of selected patients with malignant disease and non-malignant hematological disorders. However, its use is limited by availability of human leukocyte antigens (HLA)-matched donor cells, engraftment and graft-versus-host disease (GVHD). Prevention of GVHD, improvement in the speed and quality of marrow reconstitution, and screening of new immunomodulating agents which improve engraftment and augment hemopoiesis are intense areas of investigation. To this end there has clearly been progress in purification and characterization of human stem cells from different tissue sources. Discussed in this review are: (a) stem cell purification, characterization and ex vivo expansion; (b) bone marrow stem cell transplantation; (c) cord blood stem cell transplantation; (d) peripheral blood stem cell transplantation; (e) fetal liver stem cell transplantation; (f) in utero stem cell transplantation; and (g) evaluation of the capacity of stem cells to serve as targets for gene therapy.

T lymphocyte-directed gene therapy for ADA- SCID: initial trial results after 4 years

In 1990, a clinical trial was started using retroviral-mediated transfer of the adenosine deaminase (ADA) gene into the T cells of two children with severe combined immunodeficiency (ADA- SCID). The number of blood T cells normalized as did many cellular and humoral immune responses. Gene treatment ended after 2 years, but integrated vector and ADA gene expression in T cells persisted. Although many components remain to be perfected, it is concluded here that gene therapy can be a safe and effective addition to treatment for some patients with this severe immunodeficiency disease.

Heterogeneity of phenotype in two siblings with adenosine deaminase deficiency

Adenosine deaminase (ADA) deficiency is the cause of about one third of the autosomal recessively inherited cases of severe combined immunodeficiency. Disease severity in ADA deficiency is variable, presumably related in part to heterogeneity in the genotypes causing the disease. We now report on two children in a single family with ADA deficiency who presented with distinct clinical courses. One child presented with severe immunodeficiency and recurrent infections that led to the diagnosis of severe combined immunodeficiency and ADA deficiency at 7 months of age. The older child, who was diagnosed at 3 years of age (after the diagnosis of the younger child), did not have a history of serious or opportunistic infections. Although she was lymphopenic, immune responsiveness was intact, in terms of antibody production, delayed-type hypersensitivity, and in vitro T-cell function. The difference in clinical course in these two siblings is an important observation and demonstrates that the phenotypic expression of ADA deficiency can vary within a family, even in a situation in which protective isolation from infectious pathogens was not a factor in causing the milder course. These observations indicate that expression of disease severity in ADA deficiency may depend to a significant degree on environmental factors and/or on heterogeneity at other genetic loci, which may regulate or modify the expression of the ADA gene or the activity of its product. Furthermore, these observations highlight the importance of recognizing patients with ADA deficiency who present with less severe disease and support the impression that functional immunity in patients with the "late-onset" form of ADA deficiency can deteriorate over time.(ABSTRACT TRUNCATED AT 250 WORDS)

IgG antibody response to polyethylene glycol-modified adenosine deaminase in patients with adenosine deaminase deficiency

Polyethylene glycol (PEG)-modified bovine adenosine deaminase (ADA) is used for replacement therapy of severe combined immunodeficiency disease due to inherited ADA deficiency. We monitored IgG anti-ADA antibody in 17 patients treated by intramuscular injections of PEG-ADA for 1 to greater than 5.5 yr. ELISA-detectable anti-ADA IgG appeared in 10 patients, usually between the third and eighth months of treatment. Anti-ADA levels did not correlate with trough plasma ADA activity, which averaged 1.8-5 times normal blood (erythrocyte) ADA activity, depending on dose (15-60 U/kg per wk). ELISA-detectable anti-ADA antibodies were directed primarily at bovine-specific peptide (rather than PEG-containing) epitopes. Enhanced enzyme clearance, mediated by antibody that directly inhibited native and PEG-modified bovine ADA, and native, but not PEG-modified human ADA, occurred in two patients. In one, tolerance was induced; in the second, twice weekly injections of PEG-ADA compensated for accelerated clearance. We speculate that inhibitory antibodies recognize conserved, relatively PEG-free epitope(s) encompassing the active site, and that in human, but not bovine, ADA a PEG-attachment site "shields" the active site from immune recognition. We conclude that PEG-modification largely prevents the development of high affinity, or high levels of clearing antibodies to bovine ADA, and that PEG-modified human ADA should be further investigated as a possible treatment for ADA deficiency.

Gene transfer of adenosine deaminase into primitive human hematopoietic progenitor cells

The inherited deficiency in adenosine deaminase (ADA), which results in severe combined immunodeficiency, is generally regarded as an optimal model for the development of human somatic gene therapy. The ideal target for the correction of ADA deficiency and other lympho-hematopoietic disorders would be the hematopoietic stem cell. We have used a combination of recombinant human interleukins-3 and -6 to stimulate the proliferation of primitive human hematopoietic progenitor cells during a period of co-cultivation with irradiated cells producing high titers of an ADA-transducing retroviral vector packaged in amphotropic particles. In a series of nine experiments, an average of 83% of the clonogenic progenitors (CFU-E and CFU-GM) were found to have acquired the transferred sequence as determined by polymerase chain reaction analysis. In addition, in two experiments, 24-44% of the clonogenic progenitors derived from long-term myeloid cultures 9 weeks post-transduction were found to contain vector sequence. The latter cells are derived from so-called "long-term culture-initiating cells" (LTC-IC), which are primitive cells probably related to hematopoietic stem cells. Moreover, the transduced ADA enzyme was found to be expressed in both normal and ADA-deficient erythroid colonies, and in the nonadherent cells of long-term bone marrow culture for at least 2 weeks at levels that approximate the endogenous ADA levels of normal erythroid cells. These results indicate that the ADA coding sequence can efficiently be introduced by retroviral gene transfer into both committed and primitive human hematopoietic progenitor cells, and that this will result in adequate expression of the transduced enzyme in the progeny of committed hematopoietic progenitors.

Donor type natural killer cells after haploidentical T cell-depleted bone marrow stem cell transplantation in a patient with adenosine deaminase-deficient severe combined immunodeficiency

T cell-depleted haploidentical (parental) bone marrow stem cell transplants are given to most infants with the syndrome of severe combined immunodeficiency (SCID) because they have no available HLA-identical sibling potential donors. Since they usually do not undergo cytoreduction prior to transplantation, these children later demonstrate mixed hematopoietic chimerism. Most often, T cells (but usually not B lymphocytes, macrophages, or other hematopoietic cells) can be shown to be of donor type. The origin of natural killer (NK) cells in such chimeras has not been reported. Two lymphocyte lines derived from the CD16+ fraction of an adenosine deaminase (ADA)-deficient male SCID's blood mononuclear cells (MNC) 13 months following maternal marrow stem cell transplantation demonstrated typical phenotypic and functional characteristics of NK cells after expansion. Karyotyping showed both lines to be XX. Thus, NK cell engraftment can occur in SCID infants who have not been conditioned, even when significant NK cell function is present before transplantation.

Paradoxical expression of adenosine deaminase in T cells cultured from a patient with adenosine deaminase deficiency and combine immunodeficiency

T lymphocytes cultured from a patient (T.D.) with adenosine deaminase (ADA) deficiency expressed ADA activity in the normal range, inconsistent with her severe immunodeficiency, metabolic abnormalities, and with the absence of ADA activity in her B lymphocytes and other nucleated hematopoietic cells. ADA from T.D. T cells had normal Km, heat stability, and sensitivity to ADA inhibitors. Examination of HLA phenotype and polymorphic DNA loci indicated that T.D. was neither chimeric nor a genetic mosaic. Amplified and subcloned ADA cDNA from ADA+ T.D. T cells was shown by allele-specific oligonucleotide hybridization to possess the same mutations (Arg101----Trp, Arg211----His) previously found in the ADA-T.D. B cell line GM 2606 (Akeson, A. L., D. A. Wiginton, M. R. Dusing, J. C. States, and J. J. Hutton. 1988. J. Biol. Chem. 263:16291-16296). Our findings suggest that one of these mutant alleles can be expressed selectively in IL-2-dependent T cells as stable, active enzyme. Cultured T cells from other patients with the Arg211----His mutation did not express significant ADA activity, while some B cell lines from a patient with an Arg101----Gln mutation have been found to express normal ADA activity. We speculate that Arg101 may be at a site that determines degradation of ADA by a protease that is under negative control by IL-2 in T cells, and is variably expressed in B cells. Il-2 might increase ADA expression in T cells of patients who possess mutations of Arg101.

X-linked severe combined immunodeficiency. Diagnosis in males with sporadic severe combined immunodeficiency and clarification of clinical findings

Over 80% of infants with severe combined immunodeficiency (SCID) of unknown genetic etiology are males, yet less than a third of these affected males have a family history of X-linked disease. To help identify new mutations of the X-linked SCID gene and to provide genetic counseling, X chromosome inactivation patterns in T cells from 16 women who had sons with sporadic SCID were examined. Between 9 and 35 human/hamster hybrids that selectively retained the active human X chromosome were produced from the T cells of each woman and analyzed with an X-linked restriction fragment length polymorphism for which the woman in question was heterozygous. Exclusive use of a single X as the active X was seen in the T cell hybrids from 7 of the 16 women, identifying these women as carriers of X-linked SCID. Studies on additional family members confirmed the mutant nature of the inactive X and revealed the source of the new mutation in three families. To determine whether there were any laboratory characteristics that might differentiate the boys whose mothers were identified as carriers of X-linked SCID from those whose mothers were not, the clinical records of both groups were compared to each other and to a group of 14 boys with a family history of X-linked SCID. The most consistent finding in the 21 patients with X-linked SCID was an elevated proportion of B cells. These data demonstrate the high incidence of spontaneous mutation for the X-linked SCID gene and help clarify the characteristic presenting features of this disorder.

Progress toward human gene therapy

Current therapies for most human genetic diseases are inadequate. In response to the need for effective treatments, modern molecular genetics is providing tools for an unprecedented new approach to disease treatment through an attack directly on mutant genes. Recent results with several target organs and gene transfer techniques have led to broad medical and scientific acceptance of the feasibility of this "gene therapy" concept for disorders of the bone marrow, liver, and central nervous system; some kinds of cancer; and deficiencies of circulating enzymes, hormones, and coagulation factors. The most well-developed models involve alteration of mutant target genes by gene transfer with recombinant pathogenic viruses in order to express new genetic information and to correct disease phenotypes--the conversion of the swords of pathology into the plowshares of therapy.

Ecto-enzyme activity of human erythrocyte adenosine deaminase

Adenosine deaminase is found primarily in the cytoplasm of many cell types. In the human erythrocyte, about 30 per cent of the total adenosine deaminase activity is membrane associated, and about two-thirds of this is inactivated by treatment of intact erythrocytes with the nonpenetrating reagent diazotized sulfanilic acid, without affecting lactate dehydrogenase, a soluble cytoplasmic enzyme. This indicates that within the cell membranes, the catalytic site of about two-thirds of the adenosine deaminase faces the external medium, i.e., ecto adenosine deaminase. Localization of adenosine deaminase activity at the cell membrane is demonstrated directly by electron microscopy by use of the substrate 6-Chloropurine ribonucleoside, which is dechlorinated by adenosine deaminase to produce Cl-, which is precipitated at its locus of formation by added Ag+, and the precipitated AgCl converted into the electron dense Ag0 upon exposure to light. From the Hydropathic Profile of the amino acid sequence of adenosine deaminase it is evident that there are two hydrophobic domains of sufficient length to span a biological membrane, and it is proposed that these domains could function to anchor the enzyme to the membrane. The importance of adenosine deaminase is indicated by the fatal immuno-deficiency which results from untreated genetic adenosine deaminase deficiency. It may be important to determine whether the amount of ecto adenosine deaminase activity is better suited to assess the clinical status of adenosine deaminase deficient patients that the currently used total cellular enzyme activity.

Adenosine deaminase (ADA) deficiency due to deletion of the ADA gene promoter and first exon by homologous recombination between two Alu elements

In 15-20% of children with severe combined immunodeficiency (SCID), the underlying defect is adenosine deaminase (ADA) deficiency. The goal of this study was to determine the precise molecular defect in a patient with ADA-deficient SCID whom we previously have shown to have a total absence of ADA mRNA and a structural alteration of the ADA gene. By detailed Southern analysis, we now have determined that the structural alteration is a deletion of approximately 3.3 kb, which included exon 1 and the promoter region of the ADA gene. DNA sequence analysis demonstrates that the deletion created a novel, complete Alu repeat by homologous recombination between two existing Alu repeats that flanked the deletion. The 26-bp recombination joint in the Alu sequence includes the 10-bp "B" sequence homologous to the RNA polymerase III promoter. This is the first example of homologous recombination involving the B sequence in Alu repeats. Similar recombination events have been identified involving Alu repeats in which the recombination joint was located between the A and B sequences of the polymerase III split promoter. The nonrandom location of these events suggests that these segments may be hot spots for recombination.