Recent advances in cytogenetic analysis techniques such as high
resolution chromosome banding and fluorescent in situ hybridization
(FISH) together with microsatellite analysis
[24],
[25]
have enabled the detection of increasingly small chromosomal
abnormalities. The microdeletions are usually small- (4 kb) or less-
and encompass multiple genes, which may all contribute to the
phenotype. Those microdeletions, which are observed most commonly, tend
to have similar breakpoints, occurring in regions of the chromosome
where there is a repetitive DNA sequence.
Di George syndrome (velocardiofacial syndrome)
It is the commonest microdeletion syndrome and involves a deletion of
chromosome 22q11. It has an estimated incidence of 1 in 5000. Multiple
anomalies are seen including a cleft palate, velo-pharyngeal
insufficiency (causing feeding difficulties), hypocalcaemia and
immunodeficiency.
[26]
Cardiac malformations described are ventricular septal defect,
tetralogy of Fallot, interrupted aortic arch, pulmonary atresia and
truncus arteriosus.
[27]
Hypotonia is present in half of the patients. Relatively slender hands
with hypotonic and hyperextensible fingers are not uncommon. The facies
are dysmorphic with a broad nasal bridge, narrow alae nasae that are
often notched, small mouth and chin and overfolded helices. The
features vary considerably from person to person, with the speech and
swallowing difficulties being the most consistent features. There is an
excess of psychotic disorders in these individuals. The most recent
study found that more than one quarter fulfilled diagnostic criteria
for schizophrenia.
[28]
Although language and motor developmental delay and persistent
co-ordination deficits are common, intelligence is usually in the
normal range.
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