Interpreting the karyotype Lab technicians compile karyotypes and then use a spe

Question

Interpreting the karyotype

Lab technicians compile karyotypes and then use a specific notation to characterize the karyotype. This notation includes the total number of chromosomes, the sex chromosomes, and any extra or missing autosomal chromosomes. For example, 47, XY, +18 indicates that the patient has 47 chromosomes, is a male, and has an extra autosomal chromosome 18. 46, XX is a female with a normal number of chromosomes. 47, XXY is a patient with an extra sex chromosome.

B 1. What notation would you use to characterize Patient B's karyotype?

Making a diagnosis

The next step is to either diagnose or rule out a chromosomal abnormality. In a patient with a normal number of chromosomes, each pair will have only two chromosomes. Having an extra or missing chromosome usually renders a fetus inviable. In cases where the fetus makes it to term, there are unique clinical features depending on which chromosome is affected. Listed below are some syndromes caused by an abnormal number of chromosomes.

B 2. What diagnosis would you give patient B?

Diagnosis Chromosomal Abnormality Normal # of chromosomes patient's problems are due to something other than an abnormal number of chromosomes. Klinefelter's Syndrome one or more extra sex chromosomes (i.e., XXY) Down's Syndrome Trisomy 21, extra chromosome 21 Trisomy 13 Syndrome extra chromosome 13

Explanation / Answer

B1

Karyotype for patients with

Extra X chromosome - XXY / XXXY - Klinefelter syndrome

In Klinefelter syndrome it is the male fetus that gets affected by receiving an extra X chromosome. The male fetus when developed would be more or less sterile. The testes would be small and would produce very less testosterone. Males with the syndrome would normally be an inch or so above people with normal genotypes. Fetus that receives more than two X chromosomes would normally be mentally retarded. They have a greater risk of developing osteoporosis, diabetes, and other autoimmune disorders. The frequency of Klinefelter syndrome would be around 1 in every 1000 males born.

Extra Y chromosome - XXY - XYY Syndrome (super males)

The syndrome is often associated with the development of males who are often taller with above 6 feet height. They produce high levels of testosterones and are said to be fertile, who can lead their normal lives. The frequency of the syndrome would be 1 in every 1500 males born.

Reduced number of chromosome - XO - Turner syndrome.

Turner syndrome is often associated with a girl fetus that often receives only one 'X' chromosome from its parents. Such a fetus if survives then would most probably be sterile as the ovaries do not develop. They look normal but would hardly develop any secondary sexual characters. At times there would be slight mental retardation among the few of the affected people. Most of the times the syndrome would often be associated with the incidence of thyroid disease.

B2

When the number of chromosomes is normal, then there exists very minimal chance of the fetus in developing an abnormality. But at times when there is a change in the length of the chromosome, it could lead up to the abnormalities merely by the differences in the expression of a gene.

Klinefelter syndrome - In Klinefelter syndrome it is the male fetus that gets affected by receiving an extra X chromosome. The male fetus when developed would be more or less sterile. The testes would be small and would produce very less testosterone. Males with the syndrome would normally be an inch or so above people with normal genotypes. Fetus that receives more than two X chromosomes would normally be mentally retarded. They have a greater risk of developing osteoporosis, diabetes, and other autoimmune disorders. The frequency of Klinefelter syndrome would be around 1 in every 1000 males born.

Down’s syndrome – The condition is often characterized by the presence of an additional third copy of the chromosome 21 instead of the normal 2 copies. Down syndrome is often associated with mental retardation, low muscular tone, small stature, upward slant of eyes etc.

Trisomy 13 syndrome is characterized by the presence of an additional copy of the chromosome 13. Children with trisomy 13 are said to be inherited with signs of congenital heart disease, and a host of other difficulties including breathing difficulty, deafness, seizures, vision problems among others.

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