WHAT DOES TRISOMY TEST +EXAMINE?

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*If a blood sample cannot be processed by the laboratory in accordance with the principles of good laboratory practice (e.g. in the event of a low foetal DNA concentration in the sample), or if the analytical results do not provide an answer to the diagnostic question, the laboratory offers a repeat examination based on the same blood sample free of charge. Under the circumstances, the period for the delivery of test results will change from 5 to 8 days (this generally applies to about 10% of all samples).

INFORMATION FOR PROFESSIONALS

Clinical significance

TRISOMY test + can be used in early stages of pregnancy to detect other foetal chromosome aberrations provided that there are relevant reasons to use differential diagnostics to do so.

Despite their high detection sensitivity to the trisomy types monitored, TRISOMY test and TRISOMY test +, similarly to all other non-invasive prenatal tests, are considered to be forms of screening rather than diagnostic methods.

This procedure is commonly called “Non-Invasive Prenatal Testing” (NIPT), which reflects the method of obtaining blood samples used in the process. The test is based on a sample of maternal blood obtained as early as in the 10th week of pregnancy – since it is non-invasive, it poses no risk to the foetus whatsoever.

Every screen-positive test result must be confirmed by a genetic test based on a sample obtained using invasive sampling (amniocentesis or chorionic villus sampling).

A screen-negative test result means that, in connection with the chromosomes or chromosome parts studied, the examination detected no foetal DNA molecule over-/underrepresentation indicating the presence of chromosome 21, 18 or 13 trisomy, sex chromosome number abnormalities, or other chromosome disorders monitored by TRISOMY test +.

A non-informative test result means that the blood sample provided could not be processed in accordance with the standard laboratory practice (e.g. the sample contained a low proportion of foetal DNA) or the result of the screening test does not answer the diagnostic question. In the event of a non-informative test result:

• the same blood sample is analysed promptly again, free of charge, which means that the period for the delivery of test results will be prolonged from 5 to 8 days;
• we analyse a new blood sample, which has to be taken 14 days after the previous blood sample was taken.

In the event that the repeated analysis is non-informative, the laboratory will refund the patient’s payment for the test.

 

MICRODELETION SYNDROMES

Due to biological and technological limitations, the accuracy of our microdeletion syndrome examination is relatively lower compared to trisomy 21, 18, and 13. Given the generally low occurrence of microdeletions in the population, there have been no studies that would reliably validate the accuracy of our test targeting these syndromes.

Syndrome name	Lokalisation	Incidence	Deletion scope
DiGeorge syndrome	22q11	1 : 4000	3 – 5 Mb
Microdeletion syndrome	1p36	1 : 5000 – 10 000	1 – 10 Mb
Prader-Willi syndrome and Angelman syndrome	15q11	1 : 10 000 – 30 000	2 – 9 Mb
Cri-du-chat syndrome	5p15	1 : 20 000 – 50 000	5 – 35 Mb
Wolfov-Hirschhornov syndrome	4p16	1 : 50 000	2,5 – 30 Mb

 22q11 DIGEORGE SYNDROME 

The most frequent microdeletion syndrome, DiGeorge syndrome causes a severe disorder that can manifest in any system or any part of the human body. The symptoms can be treated only in some cases. The disorder is characterised by congenital heart defects (CHDs), immune system disorders, kidney defects, and cleft palate issues, frequently combined with severe mental retardation. The symptoms vary considerably. In some cases (especially those involving less pronounced symptoms), familial transmission and intrafamilial variability can be assumed.

Since CHDs may actually be the only symptom of 22q11 deletion, the syndrome is frequently indicated by prenatal genetic examinations when a congenital hear disorder is detected or when such a disorder is indicated by ultrasound screening.

1p36 DELETION SYNDROME

Similarly to DiGoerge syndrome, 1p36 deletion syndrome is one of the most frequent microdeletion syndromes. It leads to an extremely severe and untreatable disorder characterised by very heterogeneous symptoms. Its main characteristics include mental retardation combined with behavioural disturbances, growth delays, and hypotonia.

15q11 PRADER-WILLI SYNDROME & ANGELMAN SYNDROME

Although they are different from one another in terms of their clinical symptoms, both syndromes are caused by an absence or dysfunction of gene functions in one and the same critical region of chromosome 15. Although most cases are caused by a deletion affecting a critical region of chromosome 15, other cases can be caused by sporadic mutation, methylation disorders, or uniparental disomy rather than deletion. Under the circumstances, it cannot be expected that microdeletion screening will detect all actual Prader-Willi and Angelman syndrome cases.

Prader-Willi syndrome is characterised by hypotonia, poor sucking reflexes, feeding difficulties in early infancy, followed by hyperphagia and obesity from age 2 onwards. Mental retardation is relatively mild, but various other behavioural disorders are present in addition to excessive eating.

Angelman syndrome characteristics are less expressed. Usually not obvious at birth, the clinical symptoms start developing around the age of 12 months. They include psychomotor activity and speech development delays. The patient’s medium mental retardation is accompanied by progressively pronounced behavioural disturbances.

5p15 CRI-DU-CHAT SYNDROME 

Cri-du-chat syndrome is an older, cytogenetically defined syndrome (also known as Lejeune syndrome or 5p- syndrome) because more extensive deletions could already be detected using optical microscopes in the era of traditional cytogenetics.

The name “cri-du-chat” (cat’s cry) comes from the leading clinical symptom this syndrome is characterised by in the period of early infancy. Combined with characteristic facial dysmorphia, the symptom is a distinguishing feature of this syndrome in comparison to other disorders involving growth delays, psychomotor retardation, microcephaly, and hypotonia. The scope of actual deletion correlates with the severity of the patient’s disability.

4p16 WOLF-HIRSCHHORN SYNDROME

Wolf-Hirschhorn syndrome (also known as 4p- syndrome) belongs to the same group of syndromes identified by traditional cytogenetics. The severity of its clinical symptoms correlates with the actual scope of deletion. Similarly to cri-du-chat syndrome, this syndrome comes with characteristic facial dysmorphia combined with microcephaly, hypertelorism, protruding eyes, and a short philtrum. Severe growth and psychomotor retardation is accompanied by other serious symptoms, such as hypotonia, epileptic fits, and congenital development defects affecting internal organs (esp. heart and kidney defects).