Karyotype Test

This test is helpful in diagnosing the following clinical conditions.

• Several chromosomal disorders, such as Down’s syndrome, especially in mothers over 35 years of age (prenatal diagnosis)
• Stillbirths or recurrent miscarriages
• Infertility
• Hypogonadism or ambiguous genitalia
• Mental retardation
• Failure to thrive
• Delayed puberty or absence of periods
• Multiple structural and functional abnormalities
• Parents with chromosomal abnormalities and at risk of transmission of defective genes
• Sex determination
• Selected cancers and leukaemia for prognosis and evaluation of cancer stage

No special preparations or fasting is needed before the test. You may be asked to sign a consent form, as it is required for most genetic tests.

Usually, white blood cells are tested for karyotyping as they are the easiest to obtain. However, a karyotype test can also be done on tumour cells and tissues, such as amniotic fluid, chorionic villi, placenta tissue and skin.

• Blood testing: A blood sample is collected in a tube under aseptic conditions. Blood cells need three days to be prepared for further processing
• Bone marrow: A needle is inserted into a bone to reach the bone marrow- a soft gel-like tissue present in certain bones. At least five millilitres (mL) of bone marrow is collected in a syringe for analysis
• Chorionic villi sampling: Chorionic sampling is done at nine weeks of pregnancy. Some studies can be done even after conception. Chorionic villi are finger-shaped projections in the placenta. To obtain a sample, a catheter is inserted through the vagina and cervix into the placenta or a needle is inserted through the abdomen into the placenta
• Amniotic fluid: Amniotic fluid is the fluid that surrounds the baby inside the uterus. Amniotic fluid tapping or amniocentesis is done after 15 weeks of pregnancy. For this, a needle is inserted into the uterus through the abdomen, and about 30 mL of amniotic fluid is collected
• In newborns, a blood sample from the heel is taken
• Cells from the foetal tissue or from the early products of conception are grown to determine the causes of spontaneous abortion
• A swab from the cheek is used to observe sex chromosomes

Specimens obtained from the lymph nodes or tumours should be kept in a sterile container.

Most laboratories provide interpretations of their results. In some cases, it may be necessary to speak with the personnel to understand the meaning of the test results.

Normal results:

Women: 44 autosomes plus 2 XX chromosomes (karyotype: 46 XX)
Men: 44 autosomes plus 1 X and 1Y chromosome (karyotype: 46 XY)

Abnormal results:

Abnormal results of a karyotyping test can be divided into two groups:

• Abnormalities of number:
  • Trisomy 21 (Down’s syndrome)
  • Trisomy 18 (Edwards’s syndrome)
  • Trisomy 13 (Patau’s syndrome)
  • Turner’s syndrome 45, single X: Characterised by a webbed neck, short stature with renal abnormalities
  • Klinefelter’s syndrome (47 XXXY): Underdeveloped reproductive organs and secondary sexual characters, infertility and learning disabilities
  • Triple XXX syndrome: Increased risk for infertility and behavioural problems
• Abnormalities of structure:
  • Cat’s cry syndrome
  • A missing short arm of a chromosome
  • Prader Willi syndrome
  • Duplications of chromosomal material
  • Translocations of chromosomes
  • Ring chromosomes in which chromosome 13 with both short and long arms are tied together like a ring

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.