Complete DiGeorge Anomaly in the Absence of Neonatal Hypocalcemia and Velofacial and Cardiac Defects
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《小儿科》
Divisiont of Pathology, Montreal Children's Hospital, McGill University Health Center, Montreal, Quebec, Canada
ABSTRACT
We report an atypical case of complete DiGeorge (DG) anomaly that presented initially exclusively as severe combined immunodeficiency (SCID). The child had severe infections at diagnosis, in keeping with the SCID phenotype; however, normal lymphocyte counts and immunoglobulin levels were noted at admission, which delayed diagnosis. Importantly, the child presented without neonatal hypocalcemia or velofacial or cardiac abnormalities at the time of diagnosis, which masked underlying DG. This case outlines the difficulties in making the diagnosis of SCID in a timely manner and illustrates the variation in presentation of the 22q11.2 deletion syndrome. There should be a high index of suspicion for primary immunodeficiency among children with severe infections and, because management may vary, DG anomaly should be considered in the differential diagnosis of T– B+ natural killer+ SCID.
Key Words: primary immunodeficiency stem cell transplant thymic transplant fluorescence in situ hybridization
Abbreviations: DG, DiGeorge PID, primary immunodeficiency SCID, severe combined immunodeficiency BMT, bone marrow transplantation NK, natural killer
Severe combined immunodeficiency (SCID) is life-threatening and usually presents in the first few months of life. Common manifestations include failure to thrive, recurrent thrush, and respiratory infections. The hallmark of SCID is absent or poorly functioning T lymphocytes. Although children with SCID often present with lymphopenia, normal or elevated lymphocyte counts are also seen. In addition, normal levels of serum immunoglobulins are often found.1,2 Therefore, normal lymphocyte counts or immunoglobulin levels should not exclude a diagnosis of primary immunodeficiency (PID) and, among children with recurrent infections, complete evaluation of the immune system, including T, B, and natural killer (NK) cell phenotyping, is required to ensure prompt diagnosis.
DiGeorge (DG) anomaly (OMIM 188400) is caused by developmental defects in the third pharyngeal pouch and fourth pharyngeal arch.3 This disorder is clinically heterogeneous and is characterized by cardiovascular defects and thymic, parathyroid, and craniofacial anomalies.4,5 Associated problems include esophageal reflux, laryngomalacia, and delay in speech acquisition. Phenotypes range from life-threatening heart defects or T cell immunodeficiency to mild craniofacial abnormalities and developmental delays. Approximately 80% of DG anomaly cases are caused by a chromosomal deletion generally referred to as del(22)(q11.2q11.2). In fact, 22q11.2 deletion syndrome6–13 is now used to describe a heterogeneous group of disorders including DG anomaly, velocardiofacial syndrome,14 and conotruncal anomaly face syndrome and is the most common chromosomal deletion syndrome among humans, occurring with an incidence of 1 case per 3000 live births.8,11,12,14–16 Among patients with del(22), 90% have a virtually identical 3-megabase heterozygous deletion of 22q11.2 but show great clinical variability, which suggests the presence of additional genetic modifiers. Some patients have DG anomaly features in conjunction with the CHARGE association (association of coloboma, heart defect, agenesis of choanae, retardation of growth or development, genital hypoplasia, and ear anomalies or deafness)17 or in association with maternal diabetes mellitus18 and are more rarely 22q11.2 hemizygous. Others have DG anomaly features and are hemizygous for 10p13.19
In DG anomaly, the development of thymic tissue is affected; thymic defects occur for 80% of patients, leading to varying degrees of cellular immunodeficiency.20 DG-SCID describes a small subset of children with clinical features of DG anomaly and severe T-cell immunodeficiency (1–2%) attributable to absent or highly hypoplastic thymic tissue. This disorder is found often in conjunction with the CHARGE association, 22q11.2 hemizygosity (50–62% in 2 reports),21,22 or diabetic embryopathy. The profound T-cell immunodeficiency in DG-SCID is fatal without intervention within the first 2 years of life.9,23–26 Immune reconstitution is possible through infusion of peripheral mononuclear cells or bone marrow transplantation (BMT) from a genotypically HLA-identical donor or, more recently, through postnatal thymic tissue transplantation.22,27–29
We report an unusual case of DG-SCID that presented exclusively as SCID, without neonatal hypocalcemia or velofacial or cardiac abnormalities, at the time of diagnosis. The child presented with a SCID phenotype, but normal lymphocyte counts and immunoglobulin levels were noted at the initial presentation, delaying diagnosis. This case clearly shows the variation in presentation of DG anomaly, and we outline difficulties in making the diagnosis of SCID in a timely manner.
CASE REPORT
A 5-month-old male infant was admitted to our hospital with severe parainfluenza III virus bronchopneumonitis. He was born at 41 weeks, after an uneventful normal pregnancy. He had experienced recurrent thrush and more recently failure to thrive. There was no relevant family history, and there were 2 healthy siblings. On examination, the patient exhibited marked respiratory symptoms, with a respiratory rate of 70 breaths per minute, intercostal and abdominal indrawing, and bobbing of the head (evidence of marked respiratory distress). Growth failure, with height and weight below the 10th percentile, was also noted. The nasopharyngeal aspirate was exclusively positive for parainfluenza III virus. Chest radiographs showed marked pulmonary distention, with flattening of both diaphragms and diffuse bronchoalveolar infiltrates. There was no evidence of aspiration pneumonia. Biological screening showed normal absolute lymphocyte counts (9110 cells per mm3) and normal IgG (5.2 g/L), IgA (1.3 g/L), and IgM levels (0.7 g/L). Three weeks after admission, the patient's condition deteriorated rapidly and the immunology service was consulted. Lymphocyte phenotyping established the diagnosis of SCID with a T– (150 cells per mm3), B+ (3850 cells per mm3), and NK+ (550 cells per mm3) phenotype and absent T cell proliferation in response to mitogens and anti-CD3 antibody (Fig 1). No obvious dysmorphic features were observed in a thorough physical examination, including no abnormal implantation of ears or micrognathia. The child had no history of gastroesophageal or nasopharyngeal reflux. His neurocognitive development was concordant with his age. Ionized calcium levels were normal. Nonmanipulated BMT from a HLA-matched sibling donor was performed without conditioning and resulted in T-cell engraftment and resolution of pulmonary infection within 2 weeks. On the basis of the T–B+NK+ lymphocyte phenotype and the absence of obvious facial, cardiac, and calcium abnormalities, the interleukin-7 receptor genotype was investigated and was found to be normal.30 CD3 subunits, which could have explained the molecular defect alternately, were not tested at that time.31,32
One month after BMT, the child presented with generalized seizures secondary to hypocalcemia (ionized Ca2+ level of 0.84 mmol/L). Parathyroid hormone was undetectable (<10 pg/L). On the basis of the hypoparathyroidism and SCID, the possibility of DG anomaly was investigated. Cardiac ultrasound findings were normal. Chest computed tomographic scans revealed an aberrant right subclavian artery (an anatomic variation present in 1% of the population) and the absence of a thymus (Fig 2A). A fluorescence in situ hybridization study for deletions on chromosome 22q11.2, performed with fibroblasts from the patient, confirmed the diagnosis of DG anomaly (Fig 2B). Two years after BMT, our patient exhibits CD3+ and CD4+ T cell counts of 800 cells per mm3 and 500 cells per mm3, respectively, without additional treatment. Intravenous immunoglobulin supplementation that was initiated at the time of BMT was stopped, and the patient's IgG levels remain 8 g/L. His IgA and IgM levels are also within normal ranges (1.25 g/L and 0.75 g/L, respectively). The patient has normal proliferative responses to phytohemagglutinin and anti-CD3. Chimerism studies performed on circulating mononuclear cells showed that 95% of his CD3+ cells were of donor origin. In a physical examination oriented by the diagnosis of DG anomaly and performed by the geneticist who is now monitoring the child jointly, the patient exhibited delayed speech acquisition and very subtle micrognathia. There were no additional features of DG anomaly, including no hearing defect and no vertebral, ocular, or renal abnormalities. The patient's calcium level is controlled with vitamin D and calcium supplements. His neurocognitive development cannot be assessed fully at 2.5 years of age, especially in the presence of delayed speech acquisition, and needs to be reevaluated later in the child's life.
DISCUSSION
Although lymphopenia is common in SCID, infants presenting with persistent infections and failure to thrive may have normal lymphocyte counts and immunoglobulin levels, delaying the diagnosis of PID. We report an unusual case of DG anomaly presenting exclusively as T–B+NK+ SCID. In the past decade, many molecular and genetic defects causing SCID have been identified. Defects that have been defined genetically for this subset of SCID are interleukin-7 receptor deficiency, which was excluded for our patient, CD3 subunit deficiencies, and DG anomaly (reviewed in refs 1, 2, and 33). Hypocalcemia and facial or cardiac defects are the hallmarks of DG-SCID, and 1 is present in cases reported to date. For our patient, hypocalcemia was evident only at 7 months of age. Latent hypoparathyroidism in DG anomaly has been described and diagnosed even among adults during evaluation of refractory hypocalcemia.34,35 Cardiac defects may be absent in DG-SCID; however, severe hypoparathyroidism and dysmorphic facies have been associated frequently, allowing early diagnosis.36 In another specialized center that treats children with SCID routinely (Hpital Necker, Paris, France), one other child with SCID and isolated labial cleft had del22q11.2 and a similarly delayed diagnosis (Alain Fischer, MD, PhD, oral communication, 2004). However, only 50% of children with DG-SCID have del(22)(q11.2q11.2)21,22 and can thus be diagnosed on the basis of this genetic characteristic. In all other DG-SCID cases in which such a deletion is not present, diagnosis is possible only when all of the other molecular diagnoses of T–B+NK+ SCID are known and excluded or when we gain better knowledge of the exact mechanisms underlying the DG-SCID phenotype.
Several avenues of treatment have been used to treat the life-threatening immunodeficiency associated with DG-SCID. Transplantation of fetal thymus has been used historically and resulted in immune reconstitution in a few cases.37–39 Genotypically HLA-identical BMT has also been used successfully in a few cases.27,28,40 This treatment resulted in restoration of T-cell function, most likely through adoptive transfer of postthymic donor T cells, as was the case for our patient. Two different groups postulated that only postthymic lymphocytes, and not stem cells, were responsible for immune reconstitution after successful BMT. On the basis of this hypothesis, they performed peripheral blood mononuclear cell transplantation from a HLA-identical sibling. This procedure was followed by partial T-cell engraftment and immune reconstitution through adoptive transfer of mature T cells among patients.29,36 It is very likely that children with DG-SCID cannot form new thymic immigrants from infused stem cells because they have little residual, functional, thymic tissue. Transplantation of postnatal thymic tissue is a more recent therapeutic approach and is yielding very promising results.21,22,25,41 In fact, only after this procedure did episomal circular DNA excision products of T-cell receptor gene rearrangement analysis among recipients show evidence of new thymopoiesis. In SCID-DG cases with no genotypically HLA-identical donor, this is the obvious treatment. These differences in therapeutic approaches underline the importance of early diagnosis of DG anomaly.
CONCLUSIONS
There should be a high index of suspicion for PID among children with severe infections, and this diagnosis is not to be excluded on the basis of normal lymphocyte counts or immunoglobulin levels. We recommend strongly performing lymphocyte phenotyping and stimulation tests to ensure diagnosis of PID. Chromosome 22 deletions are underdiagnosed among patients with cardiac abnormalities, and screening with fluorescence in situ hybridization for chromosome 22 deletion, a widely accessible diagnostic tool in specialized centers, is increasingly part of the evaluation of congenital cardiac disorders.12,35 Patients with T–B+NK+ SCID may have the molecular defect of DG anomaly even in the absence of neonatal hypocalcemia or obvious cardiac or facial defects. Screening for chromosome 22 deletions among patients with T–B+NK+ SCID should be routine. In the absence of this chromosomal deletion, enlisting the help of a geneticist and an endocrinologist can prove useful for diagnosis. Ensuring a correct molecular diagnosis has a profound impact on genetic counseling and, most importantly, on treatment and therapeutic options for affected children.
ACKNOWLEDGMENTS
N.J., B.M., and C.M. are recipients of "Chercheur Boursier" awards from the Fondation de la Recherche en Sante au Quebec.
FOOTNOTES
Accepted Apr 8, 2005.
No conflict of interest declared.
REFERENCES
Fischer A. Human primary immunodeficiency diseases: a perspective. Nat Immunol. 2004;5 :23 –30
Buckley RH. Primary cellular immunodeficiencies. J Allergy Clin Immunol. 2002;109 :747 –757
Thomas RA, Landing BH, Wells TR. Embryologic and other developmental considerations of thirty-eight possible variants of the DiGeorge anomaly. Am J Med Genet Suppl. 1987;3 :43 –66
Kirkpatrick JA Jr, DiGeorge AM. Congenital absence of the thymus. Am J Roentgenol Radium Ther Nucl Med. 1968;103 :32 –37
Conley ME, Beckwith JB, Mancer JF, Tenckhoff L. The spectrum of the DiGeorge syndrome. J Pediatr. 1979;94 :883 –890
Alikasifoglu M, Malkoc N, Ceviz N, Ozme S, Uludogan S, Tuncbilek E. Microdeletion of 22q11 (CATCH 22) in children with conotruncal heart defect and extracardiac malformations. Turk J Pediatr. 2000;42 :215 –218
de la Chapelle A, Herva R, Koivisto M, Aula P. A deletion in chromosome 22 can cause DiGeorge syndrome. Hum Genet. 1981;57 :253 –256
Emanuel BS, McDonald-McGinn D, Saitta SC, Zackai EH. The 22q11.2 deletion syndrome. Adv Pediatr. 2001;48 :39 –73
Hong R. The DiGeorge anomaly (CATCH 22, DiGeorge/velocardiofacial syndrome). Semin Hematol. 1998;35 :282 –290
Lindsay EA, Greenberg F, Shaffer LG, Shapira SK, Scambler PJ, Baldini A. Submicroscopic deletions at 22q11.2: variability of the clinical picture and delineation of a commonly deleted region. Am J Med Genet. 1995;56 :191 –197
McDermid HE, Morrow BE. Genomic disorders on 22q11. Am J Hum Genet. 2002;70 :1077 –1088
McDonald-McGinn DM, Tonnesen MK, Laufer-Cahana A, et al. Phenotype of the 22q11.2 deletion in individuals identified through an affected relative: cast a wide FISHing net! Genet Med. 2001;3 :23 –29
Sullivan KE. DiGeorge syndrome/chromosome 22q11.2 deletion syndrome. Curr Allergy Asthma Rep. 2001;1 :438 –444
Driscoll DA, Salvin J, Sellinger B, et al. Prevalence of 22q11 microdeletions in DiGeorge and velocardiofacial syndromes: implications for genetic counselling and prenatal diagnosis. J Med Genet. 1993;30 :813 –817
Perez E, Sullivan KE. Chromosome 22q11.2 deletion syndrome (DiGeorge and velocardiofacial syndromes). Curr Opin Pediatr. 2002;14 :678 –683
Yamagishi H, Srivastava D. Unraveling the genetic and developmental mysteries of 22q11 deletion syndrome. Trends Mol Med. 2003;9 :383 –389
Pagon RA, Graham JM Jr, Zonana J, Yong SL. Coloboma, congenital heart disease, and choanal atresia with multiple anomalies: CHARGE association. J Pediatr. 1981;99 :223 –227
Wang R, Martinez-Frias ML, Graham JM Jr. Infants of diabetic mothers are at increased risk for the oculo-auriculo-vertebral sequence: a case-based and case-control approach. J Pediatr. 2002;141 :611 –617
Daw SC, Taylor C, Kraman M, et al. A common region of 10p deleted in DiGeorge and velocardiofacial syndromes. Nat Genet. 1996;13 :458 –460
Ryan AK, Goodship JA, Wilson DI, et al. Spectrum of clinical features associated with interstitial chromosome 22q11 deletions: a European collaborative study. J Med Genet. 1997;34 :798 –804
Markert ML, Alexieff MJ, Li J, et al. Postnatal thymus transplantation with immunosuppression as treatment for DiGeorge syndrome. Blood. 2004;104 :2574 –2581
Markert ML, Sarzotti M, Ozaki DA, et al. Thymus transplantation in complete DiGeorge syndrome: immunologic and safety evaluations in 12 patients. Blood. 2003;102 :1121 –1130
Muller W, Peter HH, Wilken M, et al. The DiGeorge syndrome, I: clinical evaluation and course of partial and complete forms of the syndrome. Eur J Pediatr. 1988;147 :496 –502
Muller W, Peter HH, Kallfelz HC, Franz A, Rieger CH. The DiGeorge sequence, II: immunologic findings in partial and complete forms of the disorder. Eur J Pediatr. 1989;149 :96 –103
Markert ML, Hummell DS, Rosenblatt HM, et al. Complete DiGeorge syndrome: persistence of profound immunodeficiency. J Pediatr. 1998;132 :15 –21
Bastian J, Law S, Vogler L, et al. Prediction of persistent immunodeficiency in the DiGeorge anomaly. J Pediatr. 1989;115 :391 –396
Borzy MS, Ridgway D, Noya FJ, Shearer WT. Successful bone marrow transplantation with split lymphoid chimerism in DiGeorge syndrome. J Clin Immunol. 1989;9 :386 –392
Goldsobel AB, Haas A, Stiehm ER. Bone marrow transplantation in DiGeorge syndrome. J Pediatr. 1987;111 :40 –44
Bowers DC, Lederman HM, Sicherer SH, Winkelstein JA, Chen AR. Immune constitution of complete DiGeorge anomaly by transplantation of unmobilised blood mononuclear cells. Lancet. 1998;352 :1983 –1984
Roifman CM, Zhang J, Chitayat D, Sharfe N. A partial deficiency of interleukin-7R is sufficient to abrogate T-cell development and cause severe combined immunodeficiency. Blood. 2000;96 :2803 –2807
de Saint Basile G, Geissmann F, Flori E, et al. Severe combined immunodeficiency caused by deficiency in either the or the subunit of CD3. J Clin Invest. 2004;114 :1512 –1517
Dadi HK, Simon AJ, Roifman CM. Effect of CD3 deficiency on maturation of / and / T-cell lineages in severe combined immunodeficiency. N Engl J Med. 2003;349 :1821 –1828
Fischer A. Primary immunodeficiency diseases: an experimental model for molecular medicine. Lancet. 2001;357 :1863 –1869
Hoffmann MH, Vadstrup S. DiGeorge syndrome diagnosed in a 39-year-old woman with chronic hypocalcemia [in Danish]. Ugeskr Laeger. 2000;162 :2755 –2756
Goldmuntz E, Emanuel BS. Genetic disorders of cardiac morphogenesis: the DiGeorge and velocardiofacial syndromes. Circ Res. 1997;80 :437 –443
Bensoussan D, Le Deist F, Latger-Cannard V, et al. T-cell immune constitution after peripheral blood mononuclear cell transplantation in complete DiGeorge syndrome. Br J Haematol. 2002;117 :899 –906
Cleveland WW, Fogel BJ, Brown WT, Kay HE. Foetal thymic transplant in a case of DiGeorge's syndrome. Lancet. 1968;2 :1211 –1214
August CS, Berkel AI, Levey RH, Rosen FS, Kay HE. Establishment of immunological competence in a child with congenital thymic aplasia by a graft of fetal thymus. Lancet. 1970;1 :1080 –1083
Mayumi M, Kimata H, Suehiro Y, et al. DiGeorge syndrome with hypogammaglobulinaemia: a patient with excess suppressor T cell activity treated with fetal thymus transplantation. Eur J Pediatr. 1989;148 :518 –522
Matsumoto T, Amamoto N, Kondoh T, Nakayama M, Takayanagi T, Tsuji Y. Complete-type DiGeorge syndrome treated by bone marrow transplantation. Bone Marrow Transplant. 1998;22 :927 –930
Good RA. Cellular immunology in a historical perspective. Immunol Rev. 2002;185 :136 –158(Salem Al-Tamemi, MD, Bruc)
ABSTRACT
We report an atypical case of complete DiGeorge (DG) anomaly that presented initially exclusively as severe combined immunodeficiency (SCID). The child had severe infections at diagnosis, in keeping with the SCID phenotype; however, normal lymphocyte counts and immunoglobulin levels were noted at admission, which delayed diagnosis. Importantly, the child presented without neonatal hypocalcemia or velofacial or cardiac abnormalities at the time of diagnosis, which masked underlying DG. This case outlines the difficulties in making the diagnosis of SCID in a timely manner and illustrates the variation in presentation of the 22q11.2 deletion syndrome. There should be a high index of suspicion for primary immunodeficiency among children with severe infections and, because management may vary, DG anomaly should be considered in the differential diagnosis of T– B+ natural killer+ SCID.
Key Words: primary immunodeficiency stem cell transplant thymic transplant fluorescence in situ hybridization
Abbreviations: DG, DiGeorge PID, primary immunodeficiency SCID, severe combined immunodeficiency BMT, bone marrow transplantation NK, natural killer
Severe combined immunodeficiency (SCID) is life-threatening and usually presents in the first few months of life. Common manifestations include failure to thrive, recurrent thrush, and respiratory infections. The hallmark of SCID is absent or poorly functioning T lymphocytes. Although children with SCID often present with lymphopenia, normal or elevated lymphocyte counts are also seen. In addition, normal levels of serum immunoglobulins are often found.1,2 Therefore, normal lymphocyte counts or immunoglobulin levels should not exclude a diagnosis of primary immunodeficiency (PID) and, among children with recurrent infections, complete evaluation of the immune system, including T, B, and natural killer (NK) cell phenotyping, is required to ensure prompt diagnosis.
DiGeorge (DG) anomaly (OMIM 188400) is caused by developmental defects in the third pharyngeal pouch and fourth pharyngeal arch.3 This disorder is clinically heterogeneous and is characterized by cardiovascular defects and thymic, parathyroid, and craniofacial anomalies.4,5 Associated problems include esophageal reflux, laryngomalacia, and delay in speech acquisition. Phenotypes range from life-threatening heart defects or T cell immunodeficiency to mild craniofacial abnormalities and developmental delays. Approximately 80% of DG anomaly cases are caused by a chromosomal deletion generally referred to as del(22)(q11.2q11.2). In fact, 22q11.2 deletion syndrome6–13 is now used to describe a heterogeneous group of disorders including DG anomaly, velocardiofacial syndrome,14 and conotruncal anomaly face syndrome and is the most common chromosomal deletion syndrome among humans, occurring with an incidence of 1 case per 3000 live births.8,11,12,14–16 Among patients with del(22), 90% have a virtually identical 3-megabase heterozygous deletion of 22q11.2 but show great clinical variability, which suggests the presence of additional genetic modifiers. Some patients have DG anomaly features in conjunction with the CHARGE association (association of coloboma, heart defect, agenesis of choanae, retardation of growth or development, genital hypoplasia, and ear anomalies or deafness)17 or in association with maternal diabetes mellitus18 and are more rarely 22q11.2 hemizygous. Others have DG anomaly features and are hemizygous for 10p13.19
In DG anomaly, the development of thymic tissue is affected; thymic defects occur for 80% of patients, leading to varying degrees of cellular immunodeficiency.20 DG-SCID describes a small subset of children with clinical features of DG anomaly and severe T-cell immunodeficiency (1–2%) attributable to absent or highly hypoplastic thymic tissue. This disorder is found often in conjunction with the CHARGE association, 22q11.2 hemizygosity (50–62% in 2 reports),21,22 or diabetic embryopathy. The profound T-cell immunodeficiency in DG-SCID is fatal without intervention within the first 2 years of life.9,23–26 Immune reconstitution is possible through infusion of peripheral mononuclear cells or bone marrow transplantation (BMT) from a genotypically HLA-identical donor or, more recently, through postnatal thymic tissue transplantation.22,27–29
We report an unusual case of DG-SCID that presented exclusively as SCID, without neonatal hypocalcemia or velofacial or cardiac abnormalities, at the time of diagnosis. The child presented with a SCID phenotype, but normal lymphocyte counts and immunoglobulin levels were noted at the initial presentation, delaying diagnosis. This case clearly shows the variation in presentation of DG anomaly, and we outline difficulties in making the diagnosis of SCID in a timely manner.
CASE REPORT
A 5-month-old male infant was admitted to our hospital with severe parainfluenza III virus bronchopneumonitis. He was born at 41 weeks, after an uneventful normal pregnancy. He had experienced recurrent thrush and more recently failure to thrive. There was no relevant family history, and there were 2 healthy siblings. On examination, the patient exhibited marked respiratory symptoms, with a respiratory rate of 70 breaths per minute, intercostal and abdominal indrawing, and bobbing of the head (evidence of marked respiratory distress). Growth failure, with height and weight below the 10th percentile, was also noted. The nasopharyngeal aspirate was exclusively positive for parainfluenza III virus. Chest radiographs showed marked pulmonary distention, with flattening of both diaphragms and diffuse bronchoalveolar infiltrates. There was no evidence of aspiration pneumonia. Biological screening showed normal absolute lymphocyte counts (9110 cells per mm3) and normal IgG (5.2 g/L), IgA (1.3 g/L), and IgM levels (0.7 g/L). Three weeks after admission, the patient's condition deteriorated rapidly and the immunology service was consulted. Lymphocyte phenotyping established the diagnosis of SCID with a T– (150 cells per mm3), B+ (3850 cells per mm3), and NK+ (550 cells per mm3) phenotype and absent T cell proliferation in response to mitogens and anti-CD3 antibody (Fig 1). No obvious dysmorphic features were observed in a thorough physical examination, including no abnormal implantation of ears or micrognathia. The child had no history of gastroesophageal or nasopharyngeal reflux. His neurocognitive development was concordant with his age. Ionized calcium levels were normal. Nonmanipulated BMT from a HLA-matched sibling donor was performed without conditioning and resulted in T-cell engraftment and resolution of pulmonary infection within 2 weeks. On the basis of the T–B+NK+ lymphocyte phenotype and the absence of obvious facial, cardiac, and calcium abnormalities, the interleukin-7 receptor genotype was investigated and was found to be normal.30 CD3 subunits, which could have explained the molecular defect alternately, were not tested at that time.31,32
One month after BMT, the child presented with generalized seizures secondary to hypocalcemia (ionized Ca2+ level of 0.84 mmol/L). Parathyroid hormone was undetectable (<10 pg/L). On the basis of the hypoparathyroidism and SCID, the possibility of DG anomaly was investigated. Cardiac ultrasound findings were normal. Chest computed tomographic scans revealed an aberrant right subclavian artery (an anatomic variation present in 1% of the population) and the absence of a thymus (Fig 2A). A fluorescence in situ hybridization study for deletions on chromosome 22q11.2, performed with fibroblasts from the patient, confirmed the diagnosis of DG anomaly (Fig 2B). Two years after BMT, our patient exhibits CD3+ and CD4+ T cell counts of 800 cells per mm3 and 500 cells per mm3, respectively, without additional treatment. Intravenous immunoglobulin supplementation that was initiated at the time of BMT was stopped, and the patient's IgG levels remain 8 g/L. His IgA and IgM levels are also within normal ranges (1.25 g/L and 0.75 g/L, respectively). The patient has normal proliferative responses to phytohemagglutinin and anti-CD3. Chimerism studies performed on circulating mononuclear cells showed that 95% of his CD3+ cells were of donor origin. In a physical examination oriented by the diagnosis of DG anomaly and performed by the geneticist who is now monitoring the child jointly, the patient exhibited delayed speech acquisition and very subtle micrognathia. There were no additional features of DG anomaly, including no hearing defect and no vertebral, ocular, or renal abnormalities. The patient's calcium level is controlled with vitamin D and calcium supplements. His neurocognitive development cannot be assessed fully at 2.5 years of age, especially in the presence of delayed speech acquisition, and needs to be reevaluated later in the child's life.
DISCUSSION
Although lymphopenia is common in SCID, infants presenting with persistent infections and failure to thrive may have normal lymphocyte counts and immunoglobulin levels, delaying the diagnosis of PID. We report an unusual case of DG anomaly presenting exclusively as T–B+NK+ SCID. In the past decade, many molecular and genetic defects causing SCID have been identified. Defects that have been defined genetically for this subset of SCID are interleukin-7 receptor deficiency, which was excluded for our patient, CD3 subunit deficiencies, and DG anomaly (reviewed in refs 1, 2, and 33). Hypocalcemia and facial or cardiac defects are the hallmarks of DG-SCID, and 1 is present in cases reported to date. For our patient, hypocalcemia was evident only at 7 months of age. Latent hypoparathyroidism in DG anomaly has been described and diagnosed even among adults during evaluation of refractory hypocalcemia.34,35 Cardiac defects may be absent in DG-SCID; however, severe hypoparathyroidism and dysmorphic facies have been associated frequently, allowing early diagnosis.36 In another specialized center that treats children with SCID routinely (Hpital Necker, Paris, France), one other child with SCID and isolated labial cleft had del22q11.2 and a similarly delayed diagnosis (Alain Fischer, MD, PhD, oral communication, 2004). However, only 50% of children with DG-SCID have del(22)(q11.2q11.2)21,22 and can thus be diagnosed on the basis of this genetic characteristic. In all other DG-SCID cases in which such a deletion is not present, diagnosis is possible only when all of the other molecular diagnoses of T–B+NK+ SCID are known and excluded or when we gain better knowledge of the exact mechanisms underlying the DG-SCID phenotype.
Several avenues of treatment have been used to treat the life-threatening immunodeficiency associated with DG-SCID. Transplantation of fetal thymus has been used historically and resulted in immune reconstitution in a few cases.37–39 Genotypically HLA-identical BMT has also been used successfully in a few cases.27,28,40 This treatment resulted in restoration of T-cell function, most likely through adoptive transfer of postthymic donor T cells, as was the case for our patient. Two different groups postulated that only postthymic lymphocytes, and not stem cells, were responsible for immune reconstitution after successful BMT. On the basis of this hypothesis, they performed peripheral blood mononuclear cell transplantation from a HLA-identical sibling. This procedure was followed by partial T-cell engraftment and immune reconstitution through adoptive transfer of mature T cells among patients.29,36 It is very likely that children with DG-SCID cannot form new thymic immigrants from infused stem cells because they have little residual, functional, thymic tissue. Transplantation of postnatal thymic tissue is a more recent therapeutic approach and is yielding very promising results.21,22,25,41 In fact, only after this procedure did episomal circular DNA excision products of T-cell receptor gene rearrangement analysis among recipients show evidence of new thymopoiesis. In SCID-DG cases with no genotypically HLA-identical donor, this is the obvious treatment. These differences in therapeutic approaches underline the importance of early diagnosis of DG anomaly.
CONCLUSIONS
There should be a high index of suspicion for PID among children with severe infections, and this diagnosis is not to be excluded on the basis of normal lymphocyte counts or immunoglobulin levels. We recommend strongly performing lymphocyte phenotyping and stimulation tests to ensure diagnosis of PID. Chromosome 22 deletions are underdiagnosed among patients with cardiac abnormalities, and screening with fluorescence in situ hybridization for chromosome 22 deletion, a widely accessible diagnostic tool in specialized centers, is increasingly part of the evaluation of congenital cardiac disorders.12,35 Patients with T–B+NK+ SCID may have the molecular defect of DG anomaly even in the absence of neonatal hypocalcemia or obvious cardiac or facial defects. Screening for chromosome 22 deletions among patients with T–B+NK+ SCID should be routine. In the absence of this chromosomal deletion, enlisting the help of a geneticist and an endocrinologist can prove useful for diagnosis. Ensuring a correct molecular diagnosis has a profound impact on genetic counseling and, most importantly, on treatment and therapeutic options for affected children.
ACKNOWLEDGMENTS
N.J., B.M., and C.M. are recipients of "Chercheur Boursier" awards from the Fondation de la Recherche en Sante au Quebec.
FOOTNOTES
Accepted Apr 8, 2005.
No conflict of interest declared.
REFERENCES
Fischer A. Human primary immunodeficiency diseases: a perspective. Nat Immunol. 2004;5 :23 –30
Buckley RH. Primary cellular immunodeficiencies. J Allergy Clin Immunol. 2002;109 :747 –757
Thomas RA, Landing BH, Wells TR. Embryologic and other developmental considerations of thirty-eight possible variants of the DiGeorge anomaly. Am J Med Genet Suppl. 1987;3 :43 –66
Kirkpatrick JA Jr, DiGeorge AM. Congenital absence of the thymus. Am J Roentgenol Radium Ther Nucl Med. 1968;103 :32 –37
Conley ME, Beckwith JB, Mancer JF, Tenckhoff L. The spectrum of the DiGeorge syndrome. J Pediatr. 1979;94 :883 –890
Alikasifoglu M, Malkoc N, Ceviz N, Ozme S, Uludogan S, Tuncbilek E. Microdeletion of 22q11 (CATCH 22) in children with conotruncal heart defect and extracardiac malformations. Turk J Pediatr. 2000;42 :215 –218
de la Chapelle A, Herva R, Koivisto M, Aula P. A deletion in chromosome 22 can cause DiGeorge syndrome. Hum Genet. 1981;57 :253 –256
Emanuel BS, McDonald-McGinn D, Saitta SC, Zackai EH. The 22q11.2 deletion syndrome. Adv Pediatr. 2001;48 :39 –73
Hong R. The DiGeorge anomaly (CATCH 22, DiGeorge/velocardiofacial syndrome). Semin Hematol. 1998;35 :282 –290
Lindsay EA, Greenberg F, Shaffer LG, Shapira SK, Scambler PJ, Baldini A. Submicroscopic deletions at 22q11.2: variability of the clinical picture and delineation of a commonly deleted region. Am J Med Genet. 1995;56 :191 –197
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