Genetic Screening

genetics

What are genes?

The human body is made up of billions of cells, all of which originated from the fertilised egg at conception.  While the baby is developing in the uterus, groups of cells begin to change and specialise to become different tissues and organs.  Even though the cells within the heart are very different from the cells with the kidneys or certain cells in the blood, they have one common link – they all contain Deoxyribo Nucleic Acid (DNA).

DNA carries all the information needed to make a human and differs from one person to the next.  It is often referred to as the blue print of life.  DNA is organised into ‘building blocks’ known as genes which, in turn, are packaged into microscopic structures called chromosomes.  The DNA within cells is responsible for creating each different person.  A person’s DNA blueprint is a mixture of the DNA inherited from their mother and father, which is why people commonly resemble their parents.  The re-mixing of genetic information with each new generation is vital for a healthy population, but can also create problems, if the chromosomes become altered or combined in a way that doesn’t work properly.  Genetic diseases can run in a family from one generation to the next.

Some genetic re-arrangements may not cause serious disease but can affect fertility.  If a patient is having problems achieving a pregnancy or has suffered recurrent miscarriages then it may be useful to have their genes and chromosomes checked via a blood sample.  Midland Fertility offers three types of genetic screening:

  • Cystic Fibrosis (CF)
  • chromosome analysis (karyotyping)
  • Y chromosome deletion

Cystic Fibrosis (CF)

CF is one of the most common serious genetic diseases in Caucasians.  Persistent coughing, wheezing and recurrent bouts of pneumonia are the common symptoms of this condition.  This is caused by thick, sticky mucus which builds up in the lungs and leads to repeated infections.  Treatments are constantly improving and help extend the length and quality of life of people with CF.  However, the life expectancy of a CF sufferer remains significantly reduced compared to that of the general population.

Causes of Cystic Fibrosis

Small regions of DNA within a chromosome are called genes – and an isolated number are associated with CF.  Each person has two copies of these genes and CF occurs when both copies of the same gene are defective.  If only one gene is changed, the person will not usually show any of the symptoms of CF, but will be a carrier of the faulty gene and may pass it on to their children.  About one in 20 Northern European Caucasians in the UK is a CF carrier.

How is the test carried out?

A sample of blood is taken at Midland Fertility and analysed at a specialist laboratory, where molecular biology techniques are used to scan the genes involved in CF and compare them to a CF-free standard.  Thirty three (of around 600) mutations are routinely looked for, which cover about 90% of all those mutations in the Caucasian population.

Who should be tested?

Some men are born without a vas deferens, the tube which carries sperm from the testes, and many of these men are CF carriers.  Men who need a testicular biopsy to obtain sperm for use in treatment may be at an increased risk of being a CF carrier.

Figure 1: The vas deferens is missing in many male CF carriers (courtesy of ‘Fertility & Infertility for Dummies’, published by Wiley)
Figure 1: The vas deferens is missing in many male CF carriers (courtesy of ‘Fertility & Infertility for Dummies’, published by Wiley)

Anyone – male or female – who is aware of family members who have suffered from CF may consider having the test because they may carry one of the affected genes.

What does a positive test result mean?

If tests indicate that the patient is a CF carrier, their partner is also advised to be tested for CF.  If the partner screens negative for the most common CF mutations, then half of all their children will be CF carriers, but not show signs of the condition (see figure 2).

Figure 2: Chances of children being CF carriers if one parent is a CF carrier
Figure 2: Chances of children being CF carriers if one parent is a CF carrier

If both partners carry the same altered gene – or perhaps one of the other affected genes – there is a risk that one in four of their children will have CF, one in two will be carriers of CF and one in four will be unaffected(see figure 3).

Figure 3: Chances of children having or carrying CF if both parents are CF carriers
Figure 3: Chances of children having or carrying CF if both parents are CF carriers

Of the children who are carriers or full CF sufferers, sons will be at risk of being born with a defective or absent vas deferens.  This will affect their fertility and they may need to seek help when they want to start a family.

Very rarely, CF can develop in a child when it seems as if only one parent has the affected gene.  This may be explained by the presence of a rare mutation not detectable by the screening, or a totally new spontaneous mutation may occur in the fertilised egg.

Chromosome Analysis (karyotyping)

What is a karyotype?

Chromosomes arranged in pairs according to size and shape are known as a karyotype.  Most people possess 46 chromosomes (23 pairs) in each cell.  Forty four of these are the same in both men and women.  The remaining two are the sex chromosomes and are responsible for the differences between men and women.  A woman has two identical X chromosomes while a man has one X chromosome and one Y chromosome.

Figure 4: Male karyotype showing Y chromosome
Figure 4: Male karyotype showing Y chromosome

Figure 5: Female karyotype showing 2 X chromosomes
Figure 5: Female karyotype showing 2 X chromosomes

What does an abnormal karyotype mean?

Many alterations to the number or structure of the chromosomes will result in some form of physical or mental disability, often diagnosed at birth.  Other rearrangements may be present in people with no disabilities and only become apparent when tested for later in life.  The sex chromosomes are important as they control a person’s sexual characteristics and fertility; alterations in these frequently result in a failure to conceive.  For example, Klinefelter syndrome is a common condition in infertile men, characterised by small testes and azoospermia (no sperm) and is caused by the presence of an extra X chromosome.

Although many chromosomal rearrangements can occur, they are uncommon as most embryos with abnormal karyotypes either fail to implant or miscarry.  Around 14 patients from every 1,000 tested will be affected by a chromosomal abnormality.

How is the karyotyping test carried out?

The patient’s blood sample will be taken at Midland Fertility and sent to a specialist laboratory where it is prepared so that the chromosomes can be observed under a microscope.  They are then examined by a geneticist who will arrange them into a karyotype and look for any alterations to either the number or shape of the chromosomes.

Who should be karyotype tested?

Any man with severe oligozoospermia (very few sperm in the ejaculate) or azoospermia (no sperm in the ejaculate) should have the karyotyping test.  About 12% of such men, whose infertility is not caused by a blockage of the tube carrying the sperm (the vas deferens), will have a chromosomal abnormality which can be detected with a Karyotype.  Some men having surgical sperm retrieval are also recommended to have the test.

A woman who has suffered from recurrent miscarriages may also be advised to have a karyotype test.  The cause of miscarriage may sometimes be unidentified, although some may be due to a genetic defect.  Performing karyotyping on both partners may detect the reason for the miscarriages.

Many chromosomal disorders can be inherited and karyotyping can help identify the specific gene or chromosome responsible for any genetic condition of a patient’s close relatives.

Y Chromosome Deletion

What is Y chromosome deletion?

The Y chromosome is carried only by men and is important because it contains all the genes responsible for sperm production.  The absence of a particular gene is referred to as a ‘deletion’.  Geneticists have identified regions within the Y chromosome which, if absent, cause azoospermia (no sperm in the ejaculate) or oligozoospermia (very few sperm in the ejaculate).  See figure 4 above.

How is the test carried out?

A sample of blood is taken at Midland Fertility and sent to a specialist laboratory where the sample is analysed to detect the Y chromosome and any genes which are missing in the sperm producing regions.

Who should be tested?

Men with no or very few sperm (fewer than 1 million /ml) should consider this test as they may have problems caused by a Y chromosome deletion.  Sperm which carry a deleted Y chromosome are capable of producing a healthy baby using ICSI treatment, but are likely to pass on the deletion and its problems to any boys born as a result of the treatment.

What does a positive test result mean?

Several research groups around the world are studying the effects of the Y chromosome deletions.  Before assisted conception techniques became available, deletions resulting in infertility were never passed from father to son, but may do so when using sperm known to have a Y deletion in treatment.  Ongoing research will establish how this may affect any offspring, and at this time, no definitive answer is available.  However, it is fairly certain that boys born following such treatment may also be infertile.

What happens if any of the genetic screening tests are positive?

A positive test result can have consequences for anyone trying to have a baby and also for their everyday life.  It may even affect their close relatives.  A patient will have the chance to discuss the results and possible future fertility treatment with a Midland Fertility nurse, doctor or embryologist.  It is important that the risks of continuing with treatment  are explained  and understood and any alternatives, if appropriate, can be discussed with an Midland Fertility specialist.  Midland Fertility can also arrange for a patient to see a genetic counsellor, as appropriate.

Costs

The genetic screening tests are charged individually and do not include any other treatment or procedures.  Please refer to the current List of Charges in either the Patient Finance Information leaflet or via the fees section.

Cost of cystic fibrosis genetic screening at Midland Fertility: £250.00

Cost of cystic fibrosis and karyotype genetic screening at Midland Fertility: £425.00

Cost of cystic fibrosis, karyotype and Y deletion genetic screening at Midland Fertility: £575.00

Go to the Cost Estimator©

More information

Go to the Patient Treatment Information page and download the following infosheets:

  • Counselling
  • Surgical Sperm Retrieval
  • ICSI

LU: 3/7/14/JAA