In the nucleus of each of our cells, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.
Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing. However, the DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope. Most of what researchers know about chromosomes was learned by observing chromosomes during cell division.
Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections, or “arms.” The short arm of the chromosome is labeled the “p arm.” The long arm of the chromosome is labeled the “q arm.” The location of the centromere on each chromosome gives the chromosome its characteristic shape and can be used to help describe the location of specific genes.
This provides us with a great overview of our most basic building blocks-- but what happens when our genetic material doesn't get organized appropriately? This blog will center on some of the more common chromosomal abnormalities and their subsequent presentations.
How do genetic mutations occur? Some of the most common are found below:
P – Point mutation, or any insertion/deletion entirely inside one gene
Tr - Translocation where a chromosome breaks and reattaches itself to another chromosome.
D – Deletion of a gene or genes
Dup - Duplication of a gene or genes
C – Whole chromosome extra, missing, or both - think about Down Syndrome (aka: Trisomy 21)
T – Trinucleotide repeat disorders: gene is extended in length
Down Syndrome (Trisomy 21- an extra 21st chromosome)
This can be diagnosed with prenatal screening (can find out as early as the end of the first trimester) and other genetic testing. Cognitive impairments that can vary (mild-severe), large tongue, short stature, slanted eyes, short hands, congenital heart defects. Research is still happening in the arena as they look for ways to improve intelligence in affected individuals and really figure out what the extra genetic material causes certain symptoms/characteristics.
*Keep in mind that (46, XX) and (46, XY) are considered normal for females and males respectively. 22 pairs of autosomes, and 1 pair of sex chromosomes.
Klinefelter Syndrome (47, XXY)
Nearly 60% of pregnancies with this condition will abort (miscarry). When products of conception are tested -- this can be discovered by halting the cell cycle and separating the chromosomes. Symptoms can be very subtle early on, and only become apparent as the individual gets closer to the onset of puberty. Things like gynecomastia (breast growth in males), infertility, weak muscle development and less body hair are some of the tell-tale signs. Treatments are geared towards hormone replacement therapy (testosterone), and breast removal via surgery.
Turner Syndrome (45, X)
These females have a short, webbed neck, low set ears + hairline, and a generally short stature. They often do not develop a menstrual cycle or breast with hormone treatments. Most folks with the syndrome have a normal intellectual ability with few deficits. However, they can be prone to cardiac and renal ailments. Like Klinefelter's infertility can be an issue. Treatments are also aimed at hormone replacement therapy (growth hormone + estrogen - so the individual can develop those typical female sexual characteristics.
Hemophilia A (gene defect on the X chromosome) in position q28
This condition results in a decreased production of impaired function of clotting Factor VIII. This in turn means they are at high risk of bleeding (internally/externally). Joint bleeding as well as dental related bleeding are frequently seen manifestations. Common coagulation tests like PT, PTT can screen for this condition. PTT will be increased but PT will be unaffected. More complex laboratories can actually measure the levels of FVIII in patient plasma. Once diagnosed self-treatment with recombinant FVIII can be done. This is quite expensive though. IV desmopressin can also be given to stimulate/release FVIII stores in the body. This is usually temporary, and many times has to be repeated.
Sickle cell anemia (gene defect on chromosome 11) in position p15
This is a very painful condition that primarily affects the African American population. Healthy red blood cells are smooth, round, and bendable so they can easily flow through blood vessels and carry oxygen to every part of the body. Sickle cell begins with hemoglobin, the part of the red blood cell that carries oxygen. People with sickle cell have a special type of hemoglobin that does not carry oxygen as well. After sickle hemoglobin releases oxygen, it clumps together forming a stiff rod. This causes the red blood cell to become sickled, or banana shaped. These clumps don't carry oxygen nearly as well and they get caught up in the microvasculature. As you can imagine, besides being weak, short of breath, and tired, they are also at an increased risk of strokes. Treatment is aimed at analgesia like NSAIDS, and narcotics, targeted gene therapy, and blood transfusions.
Malignant hyperthermia (gene defect on chromosome 19) in position q13.2
Earliest signs include masseter muscle contraction after succinylcholine, a rise in ETCO2 despite increase of minute ventilation, unexplained tachycardia, and muscle rigidity. An increase in body temperature in often a late sign. This condition will always get the attention of anesthesia professionals. Dantrolene and/or discontinuation of the triggering drug can help improve/treat the condition.
September 11, 2023
Author: Joshua Ishmael, MBA, MLS(ASCP)CM, NRP
Pass with PASS, LLC.