Description of tests:

The aim and purpose of genetic diagnostic testing is to:

  • Identify the genetic cause of a disease, whether present or suspected, in the patient or in his/her family (diagnostic test).
  • Confirm or rule out such genetic cause or carrier status in an asymptomatic person (pre-symptomatic or pre-symptomatic test).
  • Detect or rule out a disease in the foetus or screen for it (prenatal diagnosis or screening).

Expected benefits: the results of this study will help improve clinical management of the disease under study.

Reliability: these studies, as with all other biological tests performed in medical practice, are not 100% reliable. This is due to the limitations of the test, either because not all the genetic causes of the disease are known, or because of the limitations (sensitivity) of the technique used (detection below 100%). The report delivered to the patient will indicate the specific reliability of the test performed.


Description of the procedures:

The procedure to follow is standard for diagnosis and genetic counselling requested by the physician: it is a consultation, for clinical evaluation of the disease in the patient. A biological sample will also be obtained.

  1. Genetic counselling consultation
    A consultation to collect personal and family history, report the details of the specific test and disease, its reliability, extent and possible results, along with the expected timeframe for the report.
  2. Obtaining the sample
    The confidentiality of the samples will be protected by assigning them a specific code. The patient's sample will only be identified through the assigned code. Decoding may only be carried out by the physician in charge, or the person he/she duly authorises.
  3. Results consultation
    The results of the test will be delivered in a genetic report, indicating their validity, and the patient will be attended to in a "Genetic Counselling" consultation, explaining the clinical implication of the results. The counselling session will be used to expand on the information, interpreting the results together with the clinical and family data, and the associated report will be provided.

The specific characteristics by type of study are described below:


Postnatal studies


Biological specimens

Extracting peripheral blood samples for karyotyping or molecular studies does not require the patient to attend on an empty stomach.

The biological sample may be: 5 to 15 ml of venous blood, rubbing against the inside of the cheek, saliva to obtain buccal cells, urine or other samples.

The genetic material required for the study (DNA and/or RNA) will be extracted from the biological sample(s), and/or lymphocytes (cells in the blood) will be cultured to obtain chromosomes.



Prenatal studies


PRENATAL DIAGNOSIS is the set of techniques (invasive or non-invasive) to determine the proper formation and development of the foetus. Pregnant women should be individually assessed and informed, evaluating the specific risks associated with their pregnancy in order to offer comprehensive information and help prospective parents make decisions.

The outcomes of this study will assist in clinical management of pregnancy in terms of the risk disease.

Invasive

Monogenic diseases or chromosomal abnormalities

This consultation will be preceded by a consultation in which the patient will be informed of the specific suspected diagnosis, study characteristics, diagnostic reliability, potential results, and expected timeframe.

The patient will be given further information when delivering the results, interpreting her results and clinical data, and then referred to services that can offer guidance on managing pregnancy and postnatal development following childbirth.

The samples to be obtained can be chorionic villi, amniotic fluid or umbilical cord blood.

Non-invasive

Non-Invasive Prenatal Diagnosis (NIPD) is the analysis of foetal genetic material present in the maternal bloodstream. The advantage of this type of diagnosis is that there is no risk to the foetus or the mother.

It involves extracting two samples of 20 ml of peripheral blood at different gestational ages, as defined in each case. Under certain circumstances, a third sample may be required.

NIPD applications in our centre are currently as follows:

Foetal Sex Determination: In high-risk gestations for a sex-linked pathology of genetic origin. It allows foetal sex to be determined from the first trimester of gestation in order to rule out/recommend subsequent invasive testing. The test is based on the study of the presence/absence of the SRY gene present only in males.

Determination of foetal RhD: The aim of this study is to ascertain foetal Rh status in Rh-negative pregnancies, in order to assess for routine prenatal anti-D prophylaxis and prevent the administration of blood products to the mother-to-be when the foetus is D-negative. The test is based on the study of the presence/absence of the RHD gene which encodes for the erythrocyte D antigen in the foetus.

Kell antigen: Haemolytic disease in newborns due to Kell alloimmunisation comes from the presence of a K1/K2 foetus in a K2/K2 mother. The aim of this study is to determine the Kell antigen status of the foetus by the presence/absence of the paternal K1 allele. The results can be used to define the most appropriate clinical management for each gestation.

Non-invasive prenatal diagnosis of monogenic diseases: The aim of this study is to determine foetal status in maternal blood with respect to a specific pathological genetic variant of paternal or maternal origin* associated with a monogenic disease.

*Subject to limitations, each case needs to be initially evaluated in genetic counselling to assess the feasibility of the study.

Non-invasive prenatal testing for the most frequent aneuploidies (NIPT): This test is considered a screening tool, which will require confirmation by invasive prenatal diagnostic techniques in high-risk cases.

Variations in the number of chromosomes are called aneuploidies, the most frequent being monosomies and trisomies. Trisomies occur when there are three copies of a particular chromosome, instead of the expected two. An example is Down syndrome associated with the presence of 3 copies of chromosome 21. Monosomies occur when one of the two copies is absent.

The non-invasive prenatal aneuploidy test establishes a risk for the foetus of having an aneuploidy for chromosomes 21, 18, 13, X or Y, after evaluating the relative amount of foetal DNA in maternal blood.

The required sample is whole blood collected with a specific kit available at our centre.

Biological factors of maternal origin (maternal mosaic due to age) or foetal origin (placental or foetal mosaic) may affect the result of the analysis. A specialised consultation is therefore recommended should there be potential risks, in order to assess the results and determine the most appropriate confirmation method.

This test is not recommended when an abnormality is detected in the foetus during an ultrasound. In these cases, the obstetrician will assess the need for invasive prenatal diagnosis.


Access to the results of genetic studies:


The reports will be available in the patient's medical record and can be viewed in the patient portal.

Any centre that has requested genetic studies can check patients' results reports at the following link:



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