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Many paediatric disorders are now known to have a genetic basis. They are often the consequence of a subtle rearrangement in the DNA sequence, either a mutation (an alteration in the DNA sequence), a microdeletion (loss of a small piece of DNA), or a microduplication (repetition of a small piece of DNA sequence).

 

With the advent of new methodologies such as array-CGH, which can pick up much subtler abnormalities than was previously possible, more and more syndromes are described in the literature every year. Most of the syndromes mentioned in this section (except Fragile X) occur sporadically, i.e. they are not caused by one of the parents being a carrier of a genetic disease (in contrast refer to Heritable disorders).

 

Their risk of recurrence is usually very low, approximately 1%. It is advisable to seek genetic counselling for more information on each syndrome. A number of screening tests is available at Genomedica to examine DNA from infants and children and establish a possible genetic basis of the disease. pdf Consult our list of tests for a comprehensive list of all tests available.

Sample requirements: A sample of peripheral blood (5-10 ml) is required to extract DNA or establish a blood culture. Occasionally we may require a peripheral blood sample from the parents also.

All of the tests below are also available prenatally.

Tests

  • G-banded karyotype: a karyotype examines all 46 chromosomes in the genome using a conventional light microscope at x1,000 magnification and a type of staining known as G-banding at a resolution of about 2~5Mb. This is the most basic form of genome screening and usually the starting point of our studies.

    Chromosome studies can reveal abnormalities such as small deletions, unbalanced translocations or inversions, the presence of marker chromosomes (ESAC) and other chromosomal rearrangements that may result in chromosome imbalance. Chromosomal imbalance results in the presence of excess or lack of DNA material, which in turn is often the cause of an abnormal phenotype.


    However, in many occasions, the imbalance is small and not visible by conventional G-banded cytogenetic analysis.

    Molecular tests are now available with a much higher resolution than G-banding that may uncover subtler deletions or duplications of genetic material.(see SuperscreenTM - 21 syndromes & Superscreen ExtraTM)

kariotipos2

G-banded karyotype of a normal female.

At Genomedica we offer 3 main comprehensive molecular screens, each targeting different regions of the genome:
  • SuperscreenTM - 21 syndromes
  •  Subtelomere screening
    Τhis test uses MLPA methodology to screen a special region of the chromosome, close to the chromosome end (= the telomere), known as subtelomere. These regions are of particular interest because they are generally gene-rich. Large studies show that up to 8% of non-syndromic, idiopathic mental retardation is due to a microdeletion in the subtelomeric or telomeric region.
     

ipotelomeridiakos
FISH image showing an 18p subtelomeric deletion

Other syndromes that we can test, that are not included in the Superscreen™ kit include:

Kallman syndrome* Xp22.3 Hypogonadism and anosmia in males. Partial anosmia in transmitting females
NF2 22q12.2 Meningiomas of the brain, schwannomas
X-linked ichthyosis Xp22.32 Characteristic disorder of the skin, steroid sulphatase insufficiency
Fragile X Xq27.3 CGG expansion within FMR1 gene. Severe mental retardation, macroorchidism in males, long face (See also heritable disοrders)


This list is not exhaustive – please contact our laboratory to discuss screening options for a particular syndrome not listed here
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