DiGeorge TBX1 and 22q13.3 Deletion Syndrome Probe Combination
- TBX1, 22q11.2, Red
- N85A3, 22q13.3, Green
The TBX1 probe is 211kb, labelled in red, covers the entire TBX1 gene and includes the D22S1627 marker. The N85A3 (44kb), labelled in green, is located within 22q13.33 and covers the telomeric end of the SHANK3 gene, allowing for identification of the most distal 22q13.3 deletions. The two unique sequences act as control probes for each other and allow identification of chromosome 22.
DiGeorge syndrome1, and a variety of congenital malformation syndromes including Velocardiofacial syndrome (VCFS)2, share the deletion of chromosome 22 at 22q11.22,3,4,5.These chromosome 22 deletions are collectively coined CATCH22, a mnemonic that covers the clinical findings of Cardiac abnormality, Abnormal facies, Thymic aplasia, Cleft palate and Hypocalaemia/Hyperthyroidism due to a chromosome 22 deletion.
In addition, around 29% of nonsyndromic patients with isolated conotruncal defects have been shown to have a 22q11.2 microdeletion6. The incidence of these anomalies is estimated to be 1:4000 to 1:9700 live births7 and the deletion of 22q11.2 therefore represents one of the most common genetic defects.
A region of approximately 2Mb, referred to as the DiGeorge Critical Region (DGCR), is the most commonly deleted region and occurs in up to 90% of patients5,8,9. Within the DGCR, a minimal critical region of 300-480kb has been described10,11, containing several genes, including TUPLE1 (HIRA), TBX1, SLC25A1 (CTP) and CLTD.
22q13.3 Deletion Syndrome
The 22q13.3 deletion syndrome presents a recognisable phenotype characterised by hypotonia, delay or absence of expressive speech, global developmental delay, normal to accelerated growth and mild dysmorphic features12,13.
Some deletions of the terminal region of chromosome 22q are cytogenetically visible. However, a few cases of cryptic deletions have been reported12,14, suggesting that the actual incidence of 22q telomere deletion may be higher than previously thought.
Several observations of patients with 22q13.3 deletion showed that the SHANK3 (ProSAP2)20 gene, encoding a structural protein of the postsynaptic density of excitation synapses and expressed in the cortex and cerebellum of the brain15, was disrupted15,16,17 or deleted18, making it a candidate causative gene for this syndrome. The deletion varies dramatically in size from 130kb to 9Mb18,19,20. The use of 22q subtelomeric probes, distal to the ARSA gene, have therefore been recommended for examining all 22q13.3 deletions20,21.
I first came across Cytocell FISH probes in a previous lab I worked in and I was struck by the quality of the products. Since this time, I have been recommending and introducing Cytocell probes across all application areas — now they are the primary FISH probes used in our lab. They have an excellent range of products and their ready-to-use reagent format saves considerable time. As a matter of fact, at a recent conference there was a discussion about the lack of commercial probes for a particular disorder and I was happy to point the participants in the direction of the Cytocell catalogue, which contains the exact probes required. Elizabeth Benner, Medical Technologist at the University of Arizona Health Network
1. Pinsky L, DiGeorge AM, J Pediatr 1965;66:1049-54
2. Shprintzen RJ et al., Cleft Palate J 1978;15:56-62
3. Burn J et al., J Med Genet 1993;30:822-4
4. Wilson DI et al., J Med Genet 1993;30:852-6
5. Driscoll DA et al., J Am Hum Genet 1992;50:924-33
6. Goldmuntz E et al., J Med Genet 1993;30:807-12
7. Tezenas Du Montcel S et al., J Med Genet 1996;33:719
8. Driscoll DA et al., Am J Med Genet 1992;44(2):261-8
9. Scambler PJ et al., Genomics 1991;10:201-6
10. Halford S et al., Hum Mol Genet 1993;2(12):2099-107
11. Carlson C et al., Am J Hum Genet 1997;61:620-9
12. Phelan MC et al., Am J Med Genet 2001;101(2):91-9
13. Phelan MC. Orphanet Journal of Rare Diseases 2008, 3:14
14. Prasad C et al., Clin Genet 2000;57(2):103-9
15. Beeckers TM et al., J Neurochem 2002;81(5):903-10
16. Bonaglia MC et al., Am J Hum Genet 2001;69(2):261-8
17. Anderlid BM et al., Hum Genet 2002;110(5):439-43
18. Wilson HL et al., J Med Genet 2003;40(8):575-84
19. Dupont C et al., French Speaking Cytogeneticists Association Congress 2003
20. Luciani J et al., J Med Genet 2003;40(9):690-6
21. Chen CP et al., Prenat Diagn 2003;23(6):504-8
This product is intended to be used on Carnoy’s solution (3:1 methanol/acetic acid) fixed peripheral blood samples.