22q11.2 deletion syndrome

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22q11.2 deletion syndrome
Classification & external resources
ICD-10 D82.1
ICD-9 279.11
OMIM 188400
eMedicine med/567 

22q11.2 deletion syndrome is a disorder caused by the deletion of a small piece of chromosome 22. The deletion occurs near the middle of the chromosome at a location designated q11.2. It has a birth incidence estimated at 1:4000.

The features of this syndrome vary widely, even among members of the same family, and affect many parts of the body. Characteristic signs and symptoms include heart defects that are often present from birth, an opening in the roof of the mouth (a cleft palate or other defect in the palate), autism, other learning disabilities, recurrent infections caused by problems with the immune system, and mild differences in facial features. Affected individuals may also have kidney abnormalities, low levels of calcium in the blood (which can result in seizures), significant feeding difficulties, autoimmune disorders such as rheumatoid arthritis, and an increased risk of developing mental illnesses.[1] Microdeletions in chromosomal region 22q11 are associated with a roughly 30-fold increased risk of schizophrenia, [2] and are frequently detected in schizophrenic patients. Different studies provide different occurrence rates, ranging from 0.5 to 3%, compared with the overall 0.025% risk of the 22q11 deletion syndrome in the general population.[3]

Because the signs and symptoms of 22q11.2 deletion syndrome are so varied, different groupings of features were once described as separate conditions. These included the velo-cardio-facial syndrome (also called Shprintzen's syndrome), DiGeorge syndrome, hearing loss with craniofacial syndromes and conotruncal anomaly face syndrome, thymic hypoplasia, cleft palate, psychiatric disorders, and hypocalcaemia. Today, the name CATCH-22 syndrome is used to group them. CATCH-22 is an acronym for the list of features: C = cardiac defects, A = abnormal facies, T = thymic hypoplasia, C = cleft palate, H = hypocalcemia , 22 = microdeletions in chromosome 22.

In addition, some children with the 22q11.2 deletion were diagnosed with Opitz G/BBB syndrome and Cayler cardiofacial syndrome. Once the genetic basis for these disorders was identified, doctors determined that they were all part of a single syndrome with many possible signs and symptoms. To avoid confusion, this condition is usually called 22q11.2 deletion syndrome, a description based on its underlying genetic cause.

Contents

[edit] Symptoms

Individuals with a 22q11 deletion can suffer from a range of over 200 possible symptoms, ranging from the mild to the very serious. Possible symptoms are:

Thymus, parathyroid glands and heart derive from the same primitive embryonic structure and that is why these three organs are dysfunctioned together in this disease. Affected patients (usually children) are prone to yeast infections.

[edit] Cause

The syndrome is caused by genetic deletions (loss of a small part of the genetic material) found on the long arm of the 22nd chromosome. Some patients with similar clinical features may have deletions on the short arm of chromosome 10.

DiGeorge syndrome causes migration defects of neural crest-derived tissues, particularly affecting development of the third and fourth Branchial pouch (pharyngeal pouches).

[edit] Treatment

Although genetic transplantation methods are currently being developed by researchers, there is yet no genetic treatment of this disease. Therefore, the treatment is symptomatic, that is calcium is administered, infections are treated with antibiotics, and these patients may occasionally undergo cardiac surgery for their heart abnormalities.

[edit] Diagnosis/testing

The 22q11.2 deletion syndrome is diagnosed in individuals with a submicroscopic deletion of chromosome 22 detected by fluorescence in situ hybridization (FISH) using DNA probes from the DiGeorge chromosomal region (DGCR). Such genetic testing is widely available for the clinical and prenatal testing of the 22q11.2 deletion syndrome. Fewer than 5% of individuals with clinical symptoms of the 22q11.2 deletion syndrome have normal routine cytogenetic studies and negative FISH testing. They may have variant deletions of DiGeorge syndrome that may be detectable on a research basis only.

[edit] Genetics

22q11.2 deletion syndrome is inherited in an autosomal dominant pattern.
22q11.2 deletion syndrome is inherited in an autosomal dominant pattern.

Most people with 22q11.2 deletion syndrome are missing about 3 million base pairs (the building blocks of DNA) on one copy of chromosome 22 in each cell. This region contains about 30 genes, but many of these genes have not been well characterized. A small percentage of affected individuals have shorter deletions in the same region. This condition is often described as a contiguous gene deletion syndrome because a deletion in chromosome 22 leads to the loss of many genes.

Researchers have not yet identified all of the genes that contribute to the features of 22q11.2 deletion syndrome. They have determined that the loss of one particular gene on chromosome 22, TBX1, is probably responsible for many of the syndrome's characteristic signs (such as heart defects, a cleft palate, distinctive facial features, and low calcium levels). A loss of this gene does not appear to cause learning disabilities, however. Additional genes in the deleted region are likely to contribute to the signs and symptoms of 22q11.2 deletion syndrome.

The 22q11.2 deletion syndrome can be inherited in an autosomal dominant manner. Almost all (about 93%) of cases have a de novo (new to the family) deletion of 22q11.2 but about 7% inherit the 22q11.2 deletion from a parent. Children of individuals with deletion 22q11.2 have a 50% chance of inheriting the 22q11.2 deletion. Prenatal testing, such as amniocentesis, is available for pregnancies determined to be at risk. Also pregnancies who have findings of congenital heart disease and/or cleft palate detected by ultrasound examination may be offered prenatal testing. Genetic counseling may be helpful for families who may have DiGeorge syndrome. Because most of the signs of this cluster of defects can also be inherited as autosomal recessive or x-linked traits, only genetic testing of both parents can determine with any certainty the likelihood these anomalies occurring in any subsequent children.

[edit] Epidemiology

22q11.2 deletion syndrome affects an estimated 1 in 1800 live births. The condition may be more common, however, because some people with the deletion have few signs and symptoms and may not have been diagnosed.

[edit] Speech and Language

Current research demonstrates there is a unique profile of speech and language impairments associated with 22q11.2 deletion syndrome. Children often perform lower on speech and language evaluations in comparison to their nonverbal IQ scores. Common problems include hypernasality, language delays, and speech sound errors. (D’Antonio et al., 2000, Scherer et al., 1999, Scherer et al., 2001)

Hypernasality occurs when air escapes through the nose during the production of oral speech sounds resulting in reduced intelligibility. This is a common characteristic in the speech and language profile because 69% of children have palatal abnormalities. If the structure of the soft palate velum is such that it does not stop the flow of air from going up to the nasal cavity, it will cause hypernasal speech. This phenomenon is referred as velopharyngeal inadequacy VPI. Hearing loss can also contribute to increased hypernasality because children with hearing impairments can have difficulty self monitoring their oral speech output. The treatment options available for VPI include prosthesis and surgery. (D’Antonio et al., 2000, Eliez et al. 2000, Robin et al., 2005, Scherer et al., 1999, Solot et al. 2000).

Difficulties acquiring vocabulary and formulating spoken language (expressive language deficits) at the onset of language development are also part of the speech and language profile associated with the 22q11.2 deletion. Vocabulary acquisition is often severely delayed for preschool age children. In some recent studies, children had a severely limited vocabulary or were still nonverbal at 2-3 years of age. School age children do make progress with expressive language as they mature, but many continue to have delays and demonstrate difficulty when presented with language tasks such as verbally recalling narratives and producing longer and more complex sentences. Receptive language, which is the ability to comprehend, retain, or process spoken language, can also be impaired although not usually with the same severity as expressive language impairments. (Persson et al., 2006, Robin et al., 2005, Scherer et al., 1999, Solot et al., 2000).

Articulation errors are commonly present in children with 22q11.2 deletion syndrome. These errors include a limited phonemic (speech sound) inventory and the use of compensatory articulation strategies resulting in reduced intelligibility. The phonemic inventory typically produced consists of sounds made in the front or back of the vocal tract such as: /p/, /w/, /j/, /m/, /n/, and glottal stops. Mid vocal tract sounds are completely absent. Compensatory articulation errors made by this population of children include: glottal stops, nasal substitutions, pharyngeal fricatives, linguapalatal sibilants, reduced pressure on consonant sounds, or a combination of these symptoms. Of these errors, glottal stops have the highest frequency of occurrence. It is reasoned that a limited phonemic inventory and the use of compensatory articulation strategies is present due to the structural abnormalities of the palate. The speech impairments exhibited by this population are more severe during the younger ages and show a trend of gradual improvement as the child matures. (D’Antonio et al., 2000, Robin et al., 2005).

[edit] See also

[edit] References

  1. ^ Debbane M, Glaser B, David MK, Feinstein C, Eliez S (2006) Psychotic symptoms in children and adolescents with 22q11.2 deletion syndrome: Neuropsychological and behavioral implications. Schizophr Res 2006, 84(2- 3):187-193. PMID 16545541
  2. ^ Bassett AS, Chow EW, AbdelMalik P, Gheorghiu M, Husted J, Weksberg R (2003) The schizophrenia phenotype in 22q11 deletion syndrome. Am J Psychiatry 2003, 160(9):1580-1586. PMID 12944331
  3. ^ Horowitz A, Shifman S, Rivlin N, Pisante A, Darvasi A (2005) A survey of the 22q11 microdeletion in a large cohort of schizophrenia patients. Schizophr Res 2005, 73(2-3):263-267. PMID 15653270
  • Baldini A (2004). "DiGeorge syndrome: an update". Curr Opin Cardiol 19 (3): 201-4.  PMID 15096950
  • Maynard TM, Haskell GT, Lieberman JA, LaMantia AS (2002). "22q11 DS: genomic mechanisms and gene function in DiGeorge/velocardiofacial syndrome". Int J Dev Neurosci 20 (3-5): 407-19.  PMID 12175881
  • McDermid HE, Morrow BE (2002). "Genomic disorders on 22q11". Am J Hum Genet 70 (5): 1077-88.  PMID 11925570 Full text
  • Perez E, Sullivan KE (2002). "Chromosome 22q11.2 deletion syndrome (DiGeorge and velocardiofacial syndromes)". Curr Opin Pediatr 14 (6): 678-83.  PMID 12436034
  • Yagi H, Furutani Y, Hamada H, Sasaki T, Asakawa S, Minoshima S, Ichida F, Joo K, Kimura M, Imamura S, Kamatani N, Momma K, Takao A, Nakazawa M, Shimizu N, Matsuoka R (2003). "Role of TBX1 in human del22q11.2 syndrome". Lancet 362 (9393): 1366-73.  PMID 14585638
  • Yamagishi H, Srivastava D (2003). "Unraveling the genetic and developmental mysteries of 22q11 deletion syndrome". Trends Mol Med 9 (9): 383-9.  PMID 13129704
  • D’Antonio, Linda L.; Scherer, Nancy; Miller, Laura L.; Kalbfleisch, John H.; Bartley, James A. 2000. “Analysis of Speech Characteristics in Children with Velocardiofacial Syndrome (VCFS and Children with Phenotyhpic Overlap without VFCS.” Cleft PalateCraniofacial Journal. September, 39:5, 455-67.
  • Eliez, D.; Feinstein, C.; Palacio-Espasa, F; Spira, A.;Lacriox, M.;Pont, C.;Luthi, F.; Robert-Tissot, C.; Cramer, B.; Schorderet, D. F.; Antonarakis, S. E. 2000. “Young Children with Velo-Cardio-Facial syndrome (Catch-22). Psychological and language phenotypes.” European Child & Adolescent Psychiatry. 9: 109-1 14.
  • Gerdes, Marsha; Solot, Cynthia; Wang, Paul; McDonald, McGinn, and Sackai, Elaine H. 2001. “Taking advantage of early diagnosis: Preschool children with the 22q 11.2 deletion.” Genetics in Medicine. January/February, 3:1, 40-4.
  • Perez, Elena; Sulivan, Kathleen E. 2002. “Chromosome 22q1 1.2 deletion syndrome (DiGeorge and velocardiofacial syndromes).” Current Options in Pediatrics. 14:678-83.
  • Persson, Christina; Niklasson, Lena; Oskarsdottir, Solveig; Johansson, Susanne; Jonsson, Radi; Soderpalm, Ewa. 2006. “Language skills in 5-8-year-old children with 22q1 1 deletion syndrome.” International Journal of Language & Communication Disorders. 41:3, 3 13-33.
  • Robin, Nathaniel H.; Shprintzen, Robert J.;2005. “Defining the Clinical Spectrum Spectrum of Deletion 22q11.2”. The Journal of Pediatrics. 147:90-96
  • Scherer, Nancy J; D’Antonio, Linda L.; Kalbfleisch, John H. 1999. “Early Speech and Language Development in Children With Velocardiofacial Syndrome.” American Journal of Medical Genetics (Neuropsychiatric Genetics). 88: 714-23.
  • Scherer, Nancy J.; D’Antonio, Linda L.; Rodgers, Jennifer R. 2001. “Profiles of communication disorder in children with velocardiofacial syndrome: Comparison to children with Down syndrome.” Genetics in Medicine. January/February, 3:1, 72-8.
  • Shprintzen, Robert J.; Higgins, Anne Marie; Antshel, Kevin; Fremont, Wanda; Roizen, Nancy; Kates, Wendy. 2005. “Velo-cardio-facial syndrome.” Current Opinion in Pediatrics. 17:725-730.
  • Solot, Cynthia B. and Knightly, Carol; Handler, Steven D.; Gerdes, Marsha; McDonald-McGinn, Donna M.; Moss, Edward; Wang, Paul; Cohen, Marilyn; Randall, Peter and Larossa, Don; Driscoll, Deborah A. 2000. “Communication Disorders in the 22Q11 .2 Microdeletion Syndrome.” Journal of Communication disorders. 33: 187-204.

This article incorporates public domain text from The U.S. National Library of Medicine

[edit] External links

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