22q11.2 Deletion/Duplication, FISH
Aids in the diagnosis of 22q deletion/duplication syndromes, in conjunction with CMS/8696 Chromosome Analysis, for Congenital Disorders, Blood
Detecting cryptic translocations involving 22q11.2 that are not demonstrated by conventional chromosome studies
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
The 22q deletion syndrome and 22q duplication syndrome have overlapping phenotypes. Deletions of 22q are associated with DiGeorge and velocardiofacial syndrome. These syndromes are manifested by the presence of growth deficiency, global developmental delay, heart defect, and hearing loss. The major birth defects include palatal clefting or insufficiency and thymus aplasia. Prominent facial features are widely spread eyes, superior placement of eyebrows, downward slanting palpebral fissures with or without ptosis (droopy upper eyelid), mild micrognathia (small jaw), and a long, narrow face.
FISH studies are highly specific and do not exclude other chromosome abnormalities. For this reason, we recommend that patients suspected of having 22q deletion or duplication syndrome also have conventional chromosome studies (CMS / Chromosome Analysis, for Congenital Disorders, Blood) performed to rule out other chromosome abnormalities or translocations.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
An interpretive report will be provided.
Any individual with a normal signal pattern in each metaphase is considered negative for this probe.
Any patient with a FISH signal pattern indicating loss of the critical region (1 signal) will be reported as having a deletion of the region tested by this probe. This is consistent with a diagnosis of 22q deletion syndrome.
Any patient with a FISH signal pattern indicating duplication of the critical region (3 signals) will be reported as having a duplication of the region tested by this probe. This is consistent with a diagnosis 22q duplication syndrome.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Because FISH is not approved by the FDA, it is important to confirm 22q deletion/duplication syndrome diagnoses by other established methods, such as clinical history or physical evaluation.
FISH analysis was performed on a series of patients and results were compared to cytogenetic analyses and the patient's phenotype. Using a probe for the critical region locus (HIRA), FISH analysis of metaphase cells or interphase nuclei identified HIRA deletions or duplications in all patients with a phenotype consistent with 22q deletion or duplication syndromes. In a series of patient specimens with normal karyotypes, no deletions or duplications of the HIRA region were identified.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Ensenauer RE, Adeyinka A, Flynn HC, et al: Microduplication 22q11.2 an emerging syndrome: clinical, cytogenetic and molecular analysis of thirteen patients. Am J Hum Genet 2003;73:1027-1040
2. Yobb TM, Sommerville MJ, Willatt L, et al: Microduplication and triplication of 22q11.2: a highly variable syndrome. Am J Hum Genet 2005;76:865-876
3. Bassett AS, Chow EWC, Husted J, et al: Clinical features of 78 adults with 22q11 deletion syndrome. Am J Med Genet 2005;138A:307-313
4. Manji A, Roberson JR, Wiktor A, et al: Prenatal diagnosis of 22q11.2 deletion when ultrasound examination reveals a heart defect. Genet Med 2001;3:65-66