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Genetics

Genetics (from the Greek Genesis meaning origin) is the study of heredity and variety of live organisms, including humans.

DNA (Deoxyribonucleic acid) encodes a person’s genetic information, is the basic unit of heredity and the main component of the chromosomes contained in the nucleus. Genes are fragments of DNA. We should mention here that the human genome (the entirety of an organism’s genetic information) consists not only of nuclear DNA but also mitochondrial DNA, however nuclear DNA contains most of the genetic information that determines the appearance and functioning of a person’s organism. This information is inherited from the parents and passed on to their offspring.

Most of the cells which form the human body have 46 chromosomes. Only reproductive cells, ovum and sperm, are haploid meaning they posses 23 chromosomes. 

Cytogenetic testing involves the assessment of the number and structure (size, translocations, inversion) of chromosomes. The analysis is conducted on material taken from around 100 cells which allows for a comparative assessment of the chromosomes and an estimation of the percentage of abnormal chromosomes in a person’s organism. The result of this assessment is the karyotype- a full overview of the chromosomes. The results confirm the normal structure of the chromosomes or establish which pairs show abnormalities and what these abnormalities are.  In most cases the result is a diagnosis of a defect, however, sometimes, especially in the case of rare defects or inconclusive test results, the situation must be assessed by a clinical geneticist. nOvum employs a team of experienced clinical geneticists who offer consults both for private patients and those whose treatment is being refunded. Each genetic abnormality should be assessed by a clinical geneticist in order to determine the risk of the patient passing it on to their offspring.

The material undergoing testing is blood. The test can be conducted 6 days a week during the opening hours of nOvum’s treatment room. The patient does not need to fast before the blood is drawn and they do not require a doctor’s referral. Patients need to wait at least one day after taking antibiotics or steroids and 4-6 weeks after a blood transfusion before submitting to the test. Patients need to inform our staff if they have ever received a bone marrow transplant.

Indications:

  • a history of genetic illnesses in the patient’s family,
  • suspected genetic defects in the offspring based on a clinical overview,
  • preparation for IVF when the male infertility factor (under 5 million sperm per ml) is suspected, in which case molecular testing should also be performed to screen for the CFTR gene which determines the occurrence of cystic fibrosis, and for Y chromosome microdeletion.
  • recurring miscarriages ( at lest 3 successive miscarriage)
  • attempting a pregnancy after giving birth to a child with developmental issues or other genetic disorders,
  • primary and secondary amenorrhea, premature menopause,
  • azoospermia,
  • idiopathic infertility after a lengthy (over 2 years) treatment,
  • suspicion of genetic disorders in foetus ( analysis of amniotic fluid sampled through amniocentesis).

The Cytogenetic Laboratory in nOvum was created in 2007. The laboratory conducts cytogenetic testing (karyotyping) through banding techniques and FISH ( fluorescent in situ hybridization ) for both adults and children.

The analysis is conducted by laboratory diagnosticians with many years of experience who have specialized in medical genetics and whose experience and academic achievements have been confirmed through their work in renowned medical centres.  They are embers of Polish and international associations focused on diagnostic cytogenetics. The laboratory undergoes regular quality control- Labquality and CEQAS. 

There exist some diseases which are caused by the mutation of a single gene. Most of these are autosomal recessive disorders which means that for the disease to develop in a child, both its parents must be carriers. If that is the case the risk of the disease occurring in the child is 25%.

Cystic fibrosis

One of these disorders is cystic fibrosis one of the most commonly identified genetic disorders. Cystic fibrosis affects cells in the lungs, intestines, pancreas, liver, sweat glands and reproductive organs. Due to the disrupted transport of chloride these organs begin to produce abnormally thick mucus which damages them as a result. The main symptoms are frequent and serious infections of the respiratory system, nutritional issues, liver and pancreatic problems. The life expectancy and quality of life of people suffering from cystic fibrosis depend on the moment of diagnosis and quality of treatment. CF is a chronic illness which means that a patient requires the constant care of their family, is usually incapable of leading a normal life and requires financial assistance since the treatment of CF is very expensive. There is no cure for cystic fibrosis and the disease usually results in the premature death of the patient.

Cystic fibrosis if an autosomal recessive disorder which means that two copies of the mutated gene are required for it to develop- one from the father and one from the mother.

Those with a single mutated gene are carriers but do not suffer from CF. Usually such people are unaware of being carriers until they undergo genetic testing.

The exception are infertile men who have a higher probability of being carriers of the CFTR gene mutation in cases of obstructive azoospermia  (no sperm in the semen) and severe oligozoospermia (< 5 million sperm/ml).

This is why infertile men who have been shown to have less than 5 million sperm/ml should be tested for the mutation of the CFTR gene which causes cystic fibrosis.

  • Being a carrier of a genetic mutation does not lead to having a sick child if the other parent is not a carrier, however the risk increases to 25% when both potential parents are carriers.
  • Around 4% of all Poles (1 in 25 people, ~ 1 500 000 people) are carriers of the mutation of the CFTR gene which causes cystic fibrosis, which means that the risk of two carriers conceiving together and the probability of a sick child being born are high.
  • The testing is a very simple procedure for the patient- it only requires a sample of their blood.

Microdeletion

Microdeletion means that small fragments of the Y chromosome, including the DAZ gene which determines sperm production, are missing. It occurs in 10-15 % of men with azoospermia and severe oligozoospermia (< 5 million sperm/ml) which is why it is often tested for during the diagnosis of an infertile couple.

Deletions may occur in the following part of the Y chromosome: AZFa (proximal),  AZFb central) or AZFc (distal).

The prognosis for the successful extraction of sperm during a testicular biopsy depends on the placement of the mutation: AZFc bodes better that AZFa and AZFb. 

The Harmony prenatal tests are used to assess the risk of genetic disorders occurring in the foetus, based on the analysis of the cell-free DNA in the mother’s blood. The tests can be performed after the 10th week of pregnancy. The tests screen for trisomy- the presence of three rather than two chromosomes in a particular set- which leads to genetic disorders:

  • Trisomy 13 causes Patau Syndrome,
  • Trisomy18 causes Edwards Syndrome Trisomy 21 causes Down Syndrome.

The detection rates of these tests are very high: 99,5% in the case of Down syndrome, 98% for Edwards syndrome and 80% for Patau syndrome. The test is 99,9% specific, which means that false positives (suggesting the presence of trisomy in a healthy foetus) happen once in every 1000 cases. 

Additional information:

  • the tests can also determine the sex of the baby in singleton pregnancies
  • the tests can be performed on twin pregnancies (without determining the sex)
  • a positive result does not exclude other possible disorders
  • in less then 5% of cases a sufficient amount of foetal DNA cannot be obtained and the test cannot be conducted (this is not related to the genetic condition of the foetus).

 

 

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