Katherine Rosero
Lab Report 1: Cytogenetics and Karyotyping
Abstract:
Karyotyping can be a useful tool in diagnosing chromosomal abnormalities. In this particular case a high-risk expectant mother elected to have a karyotype of her fetus done. After collecting fetal cells from chorionic villi, a karyotype was created. The male fetus displayed aneuploidy of the sex chromosomes leading to the conclusion that the fetus will exhibit 47, XYY syndrome.
Introduction:
Cytogenetics, the study of chromosomes, and karyotyping, the technique of staining a person’s chromosomes to obtain an organized profile, are incredibly helpful tools in modern diagnostics and early detection of certain genetic disorders. There are a wide variety of reasons a person would want either themselves, their partner or fetus to be karyotyped. Current patient, female age 40, is nine weeks pregnant and concerned with the increased risk of expecting mothers over 35 giving birth to children with chromosomal abnormalities. After consulting with her obstetrician, she elects to have a karyotype done for her fetus.
Methods:
In order to produce a karyotype, first obtain cells from the specimen. These can come from a various tissue types and even from amniotic fluid (in this case from chorionic villi), but they must be first treated with chemicals to promote cell division. A second chemical is then added to stop mitosis at metaphase, when it is easiest to view the condensed chromosomes. The cells are then submerged in a hypotonic solution and a smear is created. The smear is stained using Giemsa stain and observed under a microscope. The homologous chromosomes are then paired, and all 23 pairs of chromosomes are arranged from largest to smallest, with the sex chromosomes being the last pair.
Results:
Once the karyotype was completed, it was found that the fetus displays aneuploidy. More specifically, trisomy in their sex chromosomes (Figure 1). The male fetus has two telocentric ‘Y’ chromosomes as opposed to one, that is the expected.
Figure 1
Discussion:
47, XYY syndrome the is name for the chromosomal abnormality of a male having two ‘Y’ chromosomes. Phenotypically this often displays as having tall stature, hypotonia and hypertelorism (Bardsley, et al. 2013), while generally following all other male characteristics. Developmentally, males with sex chromosome aneuploidy are 20 times more likely diagnosed to fall within the autism spectrum (Tartaglia, et al. 2017) and have other learning disabilities. However, normal life expectancy is usually observed.
Reference:
Bardsley, M Z, et al. “47,XYY Syndrome: Clinical Phenotype and Timing of Ascertainment.”
Current Neurology and Neuroscience Reports., U.S. National Library of Medicine, Oct. 2013, www.ncbi.nlm.nih.gov/pubmed/23810129.
Tartaglia, Nicole R et al. “Autism Spectrum Disorder in Males with Sex Chromosome
Aneuploidy: XXY/Klinefelter Syndrome, XYY, and XXYY” Journal of developmental and behavioral pediatrics : JDBP vol. 38,3 (2017): 197-207.
