Pediatrics

DiGeorge Syndrome

OVERVIEW: What every practitioner needs to know

Are you sure your patient has 22q11.2 deletion syndrome? What are the typical findings for this disease?

Dr. Angelo DiGeorge originally described "DiGeorge Syndrome" in 1965, as a triad of congenital absence of the thymus, hypoparathyroidism and aortic arch anomalies resulting in poor T cell production with susceptibility to infection and hypocalcemic tetany.

DiGeorge Syndrome as originally described is now more broadly recognized as a possible component of a spectrum of disorders due to a large hemizygous chromosomal deletion in the region of 22q11.2, or "22q11.2 deletion syndrome". Various studies have found that anywhere from 55% to 90% of patients with classic "DiGeorge Syndrome" (i.e. hypocalcemia, thymic hypoplasia, thymic hypoplasia conotruncal heart abnormality), have a deletion in this region.

This logically implies that there are other causes for classic "DiGeorge Syndrome", and in fact, diabetic embryopathy, unbalanced karyotypes, fetal cocaine or alcohol exposure, VACTERL association, CHARGE Syndrome, and point mutations in TBX1, have all been attributed as other causes. Furthermore, there are patients who have the deletion but do not fall into a clinically defined syndrome and conversely, some who have features of the syndrome but the mutation is not identified.

Other prominent features within the spectrum of 22q11.2 deletion syndrome include: dysmorphic facial features, palatal anomalies, speech and developmental delays and renal anomalies, with a vast clinical heterogeneity of symptoms at presentation. With these factors in mind, it is now recommended to use the 22q11.2 deletion syndrome nomenclature, and annotate as "with or without" DiGeorge anomaly as a feature.

Typical findings for DiGeorge syndrome

Significant heterogeneity is found among phenotypes associated with 22q11.2 deletion. However, typical findings include: cardiac conotruncal anomaly, hypocalcemia due to hypoparathyroidism, poor T cell production, and dysmorphic facial features.

Cardiac defects including Tetralogy of Fallot, ventriculoseptal defect, interrupted aortic arch, and truncus arteriosus, among others, occur in 77% of patients with the deletion. The presence of one of these cardiac defects on prenatal ultrasound should prompt testing for 22q11.2 deletion syndrome.

Varying degrees of immunodeficiency are also observed. This may range from mild to moderate T cell lymphopenia in the majority, with or without delayed antibody production, to complete thymic aplasia with severe immune deficiency in less than 1% of cases. Diminished thymic output contributes to immune dysfunction early in disease as assessed by TREC (T cell receptor excision circles).

Specific facial features including a bulbous nose tip, low set and posteriorly rotated ears, "simple" ear helices, hooded eyelids, a broad nasal bridge and micrognathia often (but not always) accompany the phenotype.

Velopharyngeal insufficiency is the most common palatal defect, but others including submucous cleft, overt cleft and cleft lip and palate have also been observed. Cleft palate can be a feature in approximately 11%. In about 30%, feeding difficulty and speech delay result from velopharyngeal insufficiency.

Developmental delay and behavioral and psychiatric problems have also been reported with frequency.

The absence of any given feature should not rule out the diagnosis if clinically suspected. Associations with autoimmune disease such as autoimmune cytopenias, JRA and celiac disease as well as an increase in the incidence of allergic diseases are also described.

What other disease/condition share some of these symptoms?

22q11.2 deletion syndrome should be considered in the differential diagnosis when cardiac anomalies, specifically conotruncal abnormalities, velopharyngeal insufficiency, and neonatal hypocalemia are present, as these are common prominent features.

Important:A vast heterogeneity exists among patients with the deletion, and an absence of several features should not discount the possibility of the syndrome.

Features of DiGeorge Syndrome significantly overlap with features of velocardial facial syndrome (VCFS). Both conditions are included under the term "22q11.2 deletion syndrome," although as mentioned there are some cases of classic "DiGeorge Syndrome" in which a deletion in 22q is not found.

Many of the same features of 22q11.2 deletion syndrome are also found in CHARGE syndrome (coloboma, heart anomalies, atresia of the choanae, retardation of growth/development, genital and/or urinary anomalies, ear abnormalities and deafness. This has recently been linked to mutations in CHD7.

Differential diagnoses with overlapping signs and symptoms includes: CHARGE syndrome, Kabuki syndrome, Smith Lemli Opitz syndromes, and Godlenhar syndrome with heart defects commonly seen in each of these.

What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?

Fluorescence In Situ Hybridization (FISH) for 22q11.2 is routinely used to identify the mutation, and FISH for 10p may identify a variant that is associated with deafness. Commercially available FISH for 22q11.2 deletion usually takes about 1 to 2 weeks. Atypical deletions may not be recognized with this approach, but newer chromosomal SNP arrays can even detect 22q11.2 atypical deletions.

Most cases of 22q11.2 deletion are sporadic, however, parents with a positive FISH should be offered genetic counseling as 6-10% of new cases have been reported to be familial and the incidence of autosomal dominant inheritance is rising. A FISH for 10p13-14 should be considered when the FISH for 22q11.2 is negative but there is clinical evidence supporting DiGeorge Syndrome.

Genetic testing for CHD7 mutation implicated in CHARGE should also be considered in patients who are negative for the 22q11.2 deletion.

There is a role for prenatal ultrasound in detecting abnormalities that should prompt further testing for 22q11.2. These include the heart defects noted above and polyhydramnios.

A family history of an affected parent or sibling should also prompt screening with tests such as prenatal ultrasound, echocardiography, and chorionic villus sampling or amniocentesis from which SNP or FISH can be sent. If diagnosis is confirmed or suspected, flow cytometry for lymphocyte enumeration is useful to determine the extent of the T cell deficiency.

Quantitative antibody level of IgG, IgA, IgM and IgE with specific titers to tetanus, diphtheria, and pneumococcus can aid in determining whether the T cell defect is severe enough to affect specific antibody production by B cells. Lymphocyte cultures with mitogen and/or antigen stimulation is useful for determination of T cell function, however this test is often challenging to obtain in young infants due to the large volume of blood (10ml) required for testing. Age specific norms should always be applied when interpreting immunology tests.

Testing for TREC or T cell receptor excision circles is mostly academic or for research purposes, but can provide insight into the extent of thymic output and naive cells versus antigen experienced cells in the periphery. Alternatively, if available, testing for T cells that express CD45 RA or CD45 RO can be measured by flow cytometry as a marker of naive and memory T cells respectively.

Would imaging studies be helpful? If so, which ones?

Prenatal ultrasound in detecting abnormalities that should prompt further testing for 22q11.2 deletion (heart defects, polyhydramnios).

Absence of thymic shadow on CXR can be suggestive, but not diagnostic.

Renal ultrasound to rule out kidney anomaly and other studies including X-rays and computed tomography (CT) scans of the head and sinuses may be indicated after consultation with otolaryngology.

Confirming the diagnosis

A CBC is useful to look for significant lymphopenia in these patients. Calcium, phosphorus and parathyroid hormone assay should be performed to rule out hypoparathyroidism.

Extended flow cytometry for T cells (CD3, CD4, CD8) and a basic immune screen including IgG, IgA, IgM and IgE is useful to determine the severity of the immune deficiency. Specific antibody titers to vaccines and T lymphocyte responses to mitogen stimulation or antigen stimulation in culture are also helpful depending upon patient's vaccination history and ability to withstand relatively large volume blood draws respectively.

Nationwide implementation of newborn screening for T cell lymphopenia will occur over the next several years, and some states are already actively screening. The test will not only identify newborns with Severe Combined Immunodeficiency, but also cases of 22q11.2 deletion associated with low T cell numbers. This will likely increase the number of cases diagnosed and require consultation with an immunologist for further testing and characterization of the extent of immunodeficiency.

Algorithms for responding to positive screens are currently being developed and may vary by state, but a good reference is the American College of Medical Genetics "ACT Sheet" on newborn screening for SCID.

If you are able to confirm that the patient has DiGeorge syndrome, what treatment should be initiated?

If severe cardiac anomaly is present, repair is the most urgent concern in the newborn period.

Calcium supplementation may also be required to avoid complications of tetany.

Live vaccines are contraindicated in immunodeficiency, and determination of lymphocyte function using proliferation to mitogens may be helpful in determining when live vaccines would be safe. A consultation with a Clinical Immunologist should be done.

Speech pathology consult for feeding and swallowing issues.

Consultation by ENT for palatal defects is recommended.

Antibiotic prophylaxis with trimethoprimsulfamethoxazole should be initiated in infants greater than 2 months of age with significant T cell deficiency (CD4 T cells below 500 cells/ul) or dysfunction defined by low proliferation responses to mitogens.

Infants with severe immunodeficiency should be placed in isolation supplemented with IVIG, and blood products if needed, should be irradiated and CMV negative. In severe immunodeficiency with absent or very low T cells, HLA typing should be performed to search for transplant donors. Some infants are candidates for thymic transplant and can be referred to Dr. Markert at Duke University. This is the only center worldwide where this is currently available. Adoptive transfer of mature, matched T cells is an option for reconstitution of the T cell compartment, but this method does not transfer as many naive T cells.

In general, the majority of patients will have a mild to moderate immunodeficiency and in these cases regular follow up with an immunologist and monitoring for recurrent infections is warranted. Preschool-aged children with 22q11.2 deletion should be enrolled in early intervention for developmental delay and speech therapy.

Endocrinology consultation for growth delay due to growth hormone deficiency and hypothyroidism, as well as on going issues with hypocalcemia.

What are the adverse effects associated with each treatment option?

The treatment and management of DiGeorge Syndrome or 22q11.2 deletion spans multiple specialties and a team approach is needed. Prognosis of these patients depends more on the extent of cardiac defect, and other complicating factors than on the immune system in most cases.

What are the possible outcomes of 22q11.2 deletion syndrome?

Most deaths in the newborn period are due to cardiac complications. The mortality rate in childhood in a large cohort was 4%. In patients with severe phenotype (<1%) of absent T cells, the mortality rate is high. Autoimmune disease is present in about 10% of patients, with Juvenile Idiopathic Arthritis and hematologic autoimmune diseases such as idiopathic thrombocytopenia purpura most commonly. Celiac disease and allergies are also more common in this population.

Older children can lead full and active lives. However, emotional and intellectual development may require extra support, especially if behavioral or psychiatric complications are present.

What causes this disease and how frequent is it?

In the majority of cases this syndrome is caused by a sporadic deletion in 22q11.2, deletions in 10p have also been described, and autosomal dominant inheritance is increasingly noted since patients are surviving longer and having children.

Most cases are due to sporadic hemizygous deletion in 22q11.2. It occurs in 1:3000-1:6000 live births. Males and females are equally affected. Autosomal dominant inheritance also occurs from affected an infected parent, due to the increased numbers of affected adults having children. Approximately 6-10% of new cases are familial.

How can 22q11.2 deletion syndrome be prevented?

If neither parent of a child with 22q11.2 deletion syndrome carries the mutation, there is a <1% chance of having another child with the deletion. However, when one parent has the deletion, future pregnancies carry a 50% risk of transmission. Parents can opt to screen via chorionic villus sampling early, have preimplantation genetic diagnosis, utilize donor egg or sperm or adopt.

Some cases presenting without the deletion are linked to exposure to isotretinoin. Regulation of expression of TBX1, (a gene within the 22q11.2 region responsible for some features of the syndrome) is linked to the retinoic acid pathway, and in the future may be explored as a prenatal therapeutic approach.

What is the evidence?

Several Centers have large studies on 22q11.2 deletion syndrome and management described in this article is based on the collective experience and recommendations of these large observational studies. A comprehensive understanding of the 22q11.2 deletion syndrome in adulthood is still developing, as children with the deletion are starting to be followed long term and affected patients are surviving longer and also having children with inherited mutations.

Kirkpatrick, J, DiGeorge, A. "Congenital Absence of the Thymus". American Journal of Roentgenology Radium Therapy and Nuclear Medicine. vol. 103. 1968. pp. 32-7.

(An original description of the DiGeorge Syndrome.)

Rope, A, Cragun, D, Saal, H, Hopkin, RJ. "DiGeorge Anomaly in the Absence of Chromosome 22q11.2 Deletion". J Pediatr. vol. 155. 2009. pp. 560-5.

(A retrospective review of 64 cases of clinically confirmed DiGeorge in which 45% did not have a detectable mutation in 22q11.2.)

Driscoll, DA, Budarf, ML, Emanuel, BS. "A genetic etiology for DiGeorge syndrome: consistent deletions and microdeletions of 22q11.2". Am J Hum Genet. vol. 50. 1992. pp. 924-33.

(Molecular studies in 14 patients that delineate the region of chromosome 22 critical for DG, confirming the hypothesis that submicroscopic deletions of 22q11 are etiologic in the majority of cases studied.)

McDonald-McGinn, DM, Sullivan, K. "Chromosome 22q11.2 Deletion Syndrome (DiGeorge Syndrome/Velo-cardio-facial Syndrome)". Medicine. vol. 90. 2011. pp. 1-18.

(A comprehensive review of 22q11.2 deletion syndrome.)

Lavi, RF, Kamchaisatian, W, Sleasman, JW, Martin, D, Haraguchi, S, Day, NK, Tangsinmankong, N. "Thymic output markers indicate immune dysfunction in DiGeorge Syndrome". Journal of Allergy and Clinical Immunology. vol. 118. 2006. pp. 1184-86.

(Letter to the editor linking the degree of thymic hypoplasia to immune dysfunction in DGS.)

Murphy, KC, Jones, LA, Owen, MJ. "High rates of schizophrenia in adults with velo-cardial-facial syndrome". Arch Gen Psychiatry. vol. 56. 1999. pp. 940-45.

(A study of 50 adults with VCFS using a structured clinical interview, reports that 30% had a psychotic disorder with 24% fulfilling the DSM-IV criteria for schizophrenia, suggesting that 22q11.2 may harbor a gene or genes relevant to schizophrenia in the larger population.)

Parissis, D, Milonas, I. "Chromosome 22q11.2 deletion syndrome an underestimated cause of neuropsychiatric impairment in adolescence". J Neurol. vol. 252. 2005. pp. 989-90.

(A letter to the editor illustrating a delayed diagnosis of DGS after presentation with neuropsychiatric manifestations.)

Norstman, JA, Morcus, ME, Duijff, SN, Klaassen, PW, Heineman-deBoer, JA, Beemer, FA. "The 22q11.2 deletion in children: high rate of autistic disorders and early onset of psychotic symptoms". J Am Acad Child Adolesc Psychiatry. vol. 45. 2006. pp. 1104-13.

(A study of 60 children evaluating autism spectrum disorders and symptomatology in 22q11.2 deletion syndrome.)

Woodin, M, Wang, PP, Aleman, D, McDonald-McGinn, D, Zackai, E, Moss, E. "Neuropsychological profile of children and adolescents with the 22q11.2 microdeletion". Genet Med. vol. 3. 2001. pp. 34-9.

(A descriptive and nonparametric analyses of neuropsychological data from 80 children with 22q11.2 deletion documenting behavioral phenotype of nonverbal learning disabilities, language deficits, and social-emotional concerns.)

Ongoing controversies regarding etiology, diagnosis, treatment

Nomenclature has been challenging since the "DiGeorge Syndrome" or "DiGeorge Anomaly" was first described. Overlapping syndromes such as Velocardial Facial Syndrome, for example share many of the same features. Furthermore, there are clinical cases with mutation in 22q11.2 but no features of the syndrome, and vice versa, features of the syndrome in cases without mutation.

The heterogeneous nature of presentation in 22q11.2 deletion syndrome has made it difficult to pinpoint specific genes as the cause of particular phenotypes within the 22q11.2 deletion. SNP analysis will allow improved detection of atypical mutations. Candidate genes such as TBX 1 explain some, but not all of the features. Not much is known about the maturing immune system as patients with the syndrome survive into adulthood. With increasing awareness of the disorder and better treatment outcomes, long term studies will be required to better understand the full implications of this syndrome.

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