Severe combined immunodeficiency with leukopenia (reticular dysgenesis) in siblings: immunologic and histopathologic findings

Recent advances in understanding the pathogenesis and management of reticular dysgenesis

Reticular Dysgenesis is a rare immunodeficiency which is clinically characterized by the combination of Severe Combined Immunodeficiency (SCID) with agranulocytosis and sensorineural deafness. Mutations in the gene encoding adenylate kinase 2 (AK2) were identified to cause this phenotype. In this review, we will demonstrate important clinical differences between reticular dysgenesis and other SCID entities and summarize recent concepts in the understanding of the pathophysiology of the disease and the management strategies for this difficult condition.

Reticular dysgenesis in a preterm infant: a case report

Reticular dysgenesis (RD) is a rare congenital immunodeficiency classified within the severe combined immunodeficiencies (SCIDs) and characterized by impairment of both lymphoid and myeloid cell development. Neutropenia unresponsive to recombinant human granulocyte colony-stimulating factor (rGCSF) is the hallmark of RD and the clinical course is rapidly fatal due to overwhelming infections. The authors report a female newborn at 32 weeks of gestation presenting with severe leukopenia at birth. The bone marrow showed a maturation arrest in the myeloid and lymphoid lineage. She had no response to granulocyte colony stimulating factor (rGCSF) treatment and died with sepsis at age of 2 months.

Reticular dysgenesis (aleukocytosis) is caused by mutations in the gene encoding mitochondrial adenylate kinase 2

Human severe combined immunodeficiencies (SCID) are phenotypically and genotypically heterogeneous diseases. Reticular dysgenesis is the most severe form of inborn SCID. It is characterized by absence of granulocytes and almost complete deficiency of lymphocytes in peripheral blood, hypoplasia of the thymus and secondary lymphoid organs, and lack of innate and adaptive humoral and cellular immune functions, leading to fatal septicemia within days after birth. In bone marrow of individuals with reticular dysgenesis, myeloid differentiation is blocked at the promyelocytic stage, whereas erythro- and megakaryocytic maturation is generally normal. These features exclude a defect in hematopoietic stem cells but point to a unique aberration of the myelo-lymphoid lineages. The dramatic clinical course of reticular dysgenesis and its unique hematological phenotype have spurred interest in the unknown genetic basis of this syndrome. Here we show that the gene encoding the mitochondrial energy metabolism enzyme adenylate kinase 2 (AK2) is mutated in individuals with reticular dysgenesis. Knockdown of zebrafish ak2 also leads to aberrant leukocyte development, stressing the evolutionarily conserved role of AK2. Our results provide in vivo evidence for AK2 selectivity in leukocyte differentiation. These observations suggest that reticular dysgenesis is the first example of a human immunodeficiency syndrome that is causally linked to energy metabolism and that can therefore be classified as a mitochondriopathy.

Reticular dysgenesis: HLA non-identical bone marrow transplants in a series of 10 patients

Reticular dysgenesis is a very rare congenital immunodeficiency classified within the severe combined immunodeficiencies (SCID) and characterized by impairment of both lymphoid and myeloid cell development. We report our experience in 10 patients with RD, treated between 1979 and 1999 with HLA-haploidentical hematopoietic stem cell transplantation (HSCT). All children but one were symptomatic within the first days of their lives. Five patients required two HSCT. Five patients received conditioning therapy with busulfan (16 mg/kg) and cyclophosphamide. Three of them are alive and well with myeloid and T and B cell lymphoid reconstitution, whereas two patients died (one chronic graft-versus-host disease, one pneumonitis). Transplantation without or with other conditioning regimens in the other five cases led to absent or incomplete engraftment and none of these cases survived. These results demonstrate the mandatory need for intensive conditioning before haploidentical HSCT in RD to achieve full lymphoid and myeloid engraftment.

Association of reticular dysgenesis (thymic alymphoplasia and congenital aleukocytosis) with bilateral sensorineural deafness

Reticular dysgenesis is a rare congenital disorder characterized by severe combined immunodeficiency and profound neutropenia, curable to date, only by bone marrow transplantation. This report describes the association of bilateral sensorineural deafness with this disease.

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.

Diagnosis and management of chronic neutropenia during childhood

The approach to the diagnostic evaluation of a patient with neutropenia can be guided largely by clinical history and physical examination and does not always require an extensive laboratory evaluation. Based on the history and bone marrow morphology, most children with chronic neutropenia can be classified and managed. Most patients with chronic neutropenia are free of infections and are able to maintain a normal lifestyle with no or minimal medical intervention. On the other hand, for patients with recurrent or severe infections, careful follow-up and institution of treatment are mandatory. The Food and Drug Administration has approved the use of rhG-CSF in patients with chronic neutropenia. As mentioned previously, the use of colony-stimulating factors has dramatically improved the outcome for many patients with the more severe neutropenia; however, this cytokine is expensive, so treatment should be reserved for more severely affected patients and not given just because the ANC is low. Although concerns exist regarding leukemogenic effects or eventual loss of the progenitor cell compartment driven by the continuous stimulation of rhG-CSF, at this moment, the long-term data available suggest that the chronic administration of rhG-CSF is safe.

Severe combined immunodeficiency (SCID) associated neutropenia: a lesson from monozygotic twins

A case of severe combined immunodeficiency (SCID) in monozygotic twin sisters was detected at 3 months of age with neutropenia in one twin and a normal differential count in the other. The neutropenic twin, suffering from severe skin ulcers, was successfully treated with granulocyte colony stimulating factor (G-CSF). Discordant occurrence of neutropenia in identical twins shows that there may be a non-genetic cause for the neutropenia in SCID. Suppression of myelopoiesis was probably induced by activated maternal T cells. The neutropenia in this case may thus be classified as SCID associated neutropenia, as opposed to reticular dysgenesis, in which the neutropenia is G-CSF refractory and is most probably caused by a genetic stem cell defect. A response to G-CSF in a neutropenic child with SCID can be clinically beneficial and might help to distinguish between G-CSF unresponsive reticular dysgenesis and G-CSF responsive SCID associated neutropenia.

Pathology of the pancreas in severe combined immunodeficiency and DiGeorge syndrome: acute graft-versus-host disease and unusual viral infections

Review of autopsies of 28 children with severe combined immunodeficiency (SCID) or combined immunodeficiency (CID) and three with DiGeorge syndrome showed a high incidence of acute graft-versus-host disease (GVHD) in the pancreas. Acute GVHD (seven cases: four SCID, two CID, and one DiGeorge syndrome) was characterized by lymphocytes around large to medium ducts, damage to ductal epithelium (focal necrosis, reactive nuclear changes, inspissated secretions in duct lumens), and periductal edema. Changes were judged indeterminate but suspicious for GVHD when ductal damage was slight (six cases: three SCID, two CID, and one DiGeorge syndrome). All patients with pancreatic GVHD had received allogeneic bone marrow, fetal liver or thymus transplant, or nonirradiated blood products and had evidence of GVHD in other organs. Immunoperoxidase stain for HLA-DR showed strong-to-moderate staining of duct epithelium in two of four GVHD cases for which blocks were available. This change was nonspecific; weaker staining for HLA-DR was seen in cases with nonspecific abnormalities and in viral pancreatitis. Four cases had histological evidence of viral infection: two had cytomegalovirus pancreatitis, one had patchy parenchymal necrosis caused by adenovirus, and one had giant cell pancreatitis caused by parainfluenza virus. Mild nonspecific changes, such as focal fat necrosis or acinar dilatation, were seen in seven cases. One case had unexplained marked pancreatic atrophy and fibrosis. Acute pancreatic GVHD is not uncommon in autopsies of children with congenital immune deficiencies with GVHD of other organs; however, this finding may not have strong clinical implications in this group of patients. Careful attention to pancreatic ducts is necessary for diagnosis. Unusual viral pancreatitis may also be seen in this group, as well as nonspecific abnormalities.

Dyshematopoiesis in combined immune deficiency with congenital neutropenia

This report describes a patient with combined immune deficiency associated with congenital neutropenia (CID/CN) and reports a partial characterization of his hematopoietic abnormalities. The CID/CN syndrome described is characterized by neutropenia and by deficiencies in B-lymphoid and T-lymphoid cell number and function. Red cell and platelet counts were normal. In vitro assays indicate that the myeloid lineage was developmentally arrested at the level of the committed monocyte/granulocyte progenitor (CFU-GM), while precursors to the CFU-GM progenitor were normal. In vitro studies showed that the defect in myeloid development was not corrected with G-CSF or GM-CSF. However, combinations of cytokines present in conditioned media from the T-cell lines MO or C5MJ, or defined multiple cytokine combinations containing IL-1, IL-3, GM-CSF, kit ligand, IL-6, and IL-9, restored myelopoiesis in-vitro. In contrast, C5MJ-conditioned media did not correct deficiencies in immune function in the patient's lymphocytes and accessory cells. No abnormalities in the production of G-CSF, GM-CSF, M-CSF, or IL-1 from the patient could be identified to account for the defects in myelopoiesis orimmune function.

Pathology of the liver in severe combined immunodeficiency and DiGeorge syndrome

Review of liver biopsy or autopsy material from 33 patients with severe combined immunodeficiency or combined immunodeficiency and four patients with DiGeorge syndrome revealed a wide range of hepatic pathology. The most common abnormality was graft-versus-host disease (16 patients), followed by viral infection (4 patients had adenovirus hepatitis, 3 had cytomegalovirus hepatitis). Centrilobular fibrosis with or without veno-occlusive disease was seen in five patients. Three patients had nonspecific hepatitis, four had changes attributed to total parenteral nutrition, and two had lymphoproliferative disorders involving the liver. Both patients with lymphoproliferative disorders had received transplants. Two patients had resolving necrosis probably secondary to non-A, non-B hepatitis. One had atypical mycobacterial infection. Hemosiderosis was a common nonspecific abnormality, seen in nine patients. All patients with hepatic graft-versus-host disease had received transplants or nonirradiated blood products. Hepatic graft-versus-host disease varied in severity from hepatic necrosis with destruction of both large and small bile ducts in a transfusion-associated case to subtle damage to interlobular bile ducts. Even minimal bile duct changes correlated with the clinical impression of graft-versus-host disease in these patients. Late chronic graft-versus-host disease was not seen in any patient, although acute graft-versus-host disease sometimes occurred late after transplant.

Severe combined immune deficiency presenting with cyclic hematopoiesis

At age 2 months a male infant presented with a cyclic clinical syndrome every 14-21 days that included pharyngeal aphthous ulcers, high fever, lymphadenopathy, pallor, and malaise. Serial blood studies indicated cycling of all blood cell elements, compatible with a diagnosis of cyclic hematopoiesis (CH). He also manifested a progressively severe immune deficiency, not described before in human CH. When first studied at age 5 months, he was hypogammaglobulinaemic with normal B lymphocyte numbers. By 6.5 months, he was agammaglobulinaemic. At age 8 months, he developed severe pneumocystis carinii pneumonia, and studies showed a state of severe combined immune deficiency. The patient received a bone marrow transplant from his HLA-identical sister with no preconditioning therapy. Subsequently, normal immune function developed and the cyclic hematopoiesis resolved. The majority of lymphocytes is of donor origin. Persistence of erythrocytes and neutrophils of recipient origin suggests that the hematopoietic stem cells were not abnormal. We speculate that this patient had a primary deficiency of a differentiation factor affecting maturation of lymphoid and myeloid progenitor cells.

Elevated erythrocyte adenosine deaminase activity in a patient with primary acquired sideroblastic anemia

We report a case of primary acquired sideroblastic anemia (PASA) associated with elevated erythrocyte adenosine deaminase (ADA) activity. The patient was an 85-year-old Japanese male. Analysis of the peripheral blood revealed pancytopenia, and the bone marrow findings showed marked ringed sideroblasts and chromosomal deletion (46XY, 11q-). The erythrocyte ADA activity was 17 times higher than that of normal control, the leukocyte ADA activity was within the normal range, and the plasma ADA activity was 2 times higher than the normal mean. The adenine nucleotides in the patient's erythrocytes were within normal range. According to starch gel electrophoresis, ADA isozyme of the patient was ADA 1. Western blotting showed an increased amount of ADA protein in the patient's erythrocytes. Southern blotting revealed no gene amplification or large structural change. Dot blot analysis of the reticulocyte mRNA showed no increase in the amount of ADA mRNA in the patient's reticulocytes compared with those of reticulocyte-rich controls. We considered that the mechanism of elevated ADA activity in this acquired defect was similar to that found in hereditary hemolytic anemia associated with ADA overproduction.

Elevated erythrocyte adenosine deaminase activity in patients with acquired immunodeficiency syndrome

Acquired immunodeficiency syndrome (AIDS) is an often fatal disease caused by a retrovirus frequently resulting in malignancy and/or opportunistic infection. Because the immune deficiency in AIDS is similar to that in some purine enzyme deficiencies, we measured erythrocyte adenosine deaminase (ADA) and purine nucleoside phosphorylase activities in patients with AIDS, heterosexual controls, and a high-risk asymptomatic population. We found that erythrocyte ADA activity was significantly elevated in patients with AIDS (40 +/- 11 nmol/mg of hemoglobin per hr, mean +/- SD) relative to heterosexual controls (25 +/- 10, P less than 0.001). We also measured ADA activity in a group of individuals at high risk for AIDS and found that approximately half had significantly elevated ADA activities (45 +/- 4, P less than 0.002) that correlated with the presence of antibody to the lymphadenopathy retrovirus. Purine nucleoside phosphorylase activity was relatively normal in patients with AIDS as well as in individuals at risk for AIDS. Increased ADA appears to be a diagnostic marker of AIDS and may be useful in conjunction with antibody to the AIDS-related retrovirus in detecting the presence of infection in asymptomatic high-risk individuals. These data also suggest that, in addition to the lymphocyte, the erythroid cell line may also be infected by the AIDS-related retrovirus.

Successful bone-marrow transplantation for reticular dysgenesis

A male infant with reticular dysgenesis received a bone-marrow transplant from his HLA-identical brother. Severe graft-versus-host disease developed but he responded to high-dose methylprednisolone. 3 years after grafting, the child is thriving with full haematological reconstitution and normal cell-mediated and humoral immunity. This is the first report of the survival beyond 17 weeks of a child with reticular dysgenesis.