Chromosomal Trisomies - Types, Symptoms, Diagnosis, and Treatment

Introduction

The thread-like chromosomes that carry the genomic information from cell to cell are made of protein and a single DNA molecule. There are 23 pairs of 46 chromosomes in each cell. The most frequent cause of abnormal chromosomes is an error during cell division. Chromosome abnormalities frequently result from 1 or more of the following:

• Errors occur when sex cells divide (meiosis).

• Errors occur when other cells divide (mitosis).

Chromosomes are made up of 23 pairs in humans, including 44 chromosomes that control growth and function and two sex chromosomes that determine sex. A change in the number or genetic makeup of chromosomes results in a chromosome condition.

There are various chromosomal abnormalities, including the following:

• Aneuploidy is a condition in which chromosome gain or loss occurs due to improper gene segregation during cell division. It may result in monosomy, trisomy, tetrasomy, etc.

• When the process of cytokinesis during cell division fails, a condition known as polyploidy results, increasing the number of all the chromosomes. It is most often seen in plants.

In humans, trisomy refers to the presence of an extra copy of a chromosome in one of the pairs, and monosomy refers to the absence of one of the chromosomes from the pair.

What Is Trisomy?

Trisomies are syndromes brought on by the presence of an extra copy of an autosomal chromosome, either in its entirety or in a specific region (all chromosomes normally come in pairs). However, most expecting parents are aware of Down syndrome and will have prenatal testing to look for it; other potentially more dangerous trisomies can happen, such as Edwards syndrome, Patau syndrome, and others.

On chromosomes, there are genes that house all of the DNA-coded data pertaining to physiologic makeup and metabolic function. There are 46 chromosomes in the nucleus of every human cell, 23 of which come from each genetic parent. 22 of them are autosome pairs, which are what give us our particular biological and physiological characteristics. Sex chromosomes (X or Y) make up the 23rd pair and are a major determinant of biological sex.

Rarely, a cell division during fetal development can result in a coding error. The newly divided chromosome will contain additional genetic material in place of splitting cleanly into two identical chromosomes. A trisomy, which translates to "three bodies," is created when a third chromosome forms and joins a pair of chromosomes that normally only contain two each. This may result in a full trisomy (where a third chromosome is created completely) or a partial trisomy (where only part of the chromosome is copied). From this point on, as the cell keeps dividing, the error will keep happening over and over.

Trisomy develops during fertilization. It occurs randomly, and the diagnosis is unrelated to anything the pregnant parent did. Pregnant women over 35 are more likely to experience trisomy in their unborn child.

What Are the Different Types of Trisomy Disorders?

Based on the chromosome that has a third copy, the healthcare provider will assign a numbered diagnosis to a trisomy disorder. The location where the third copy attaches can have an impact on the genetic condition of the baby because each chromosome plays a different role in the body's blueprint. The most prevalent trisomy ailments include:

• Trisomy 13 (Patau syndrome).

• Trisomy 18 (Edward syndrome).

• Trisomy 21 (Down syndrome).

The 23rd pair of chromosomes in the genetic code are the sex cells, which determine gender. Instead of a number, sex cells are designated as XX for females or XY for males. The sex cells may duplicate abnormally during cell division, leading to a trisomy. Sex cell trisomies come in various forms.

• Trisomy X (XXX).

• Klinefelter syndrome (XXY).

• Jacob's syndrome (XYY).

What Are the Pregnancy-Related Signs and Symptoms of Trisomy?

The healthcare professional will search for indications of trisomy conditions, such as:

• Extra amniotic fluid surrounds the child.

• There is just one artery in the umbilical cord.

• Small placenta.

• The baby is less active.

• The baby is small for its age.

• Physical anomalies like a cleft palate or heart issues.

What Signs of Trisomy Are Present Once the Child Is Born?

The signs and symptoms the baby will experience will depend on the type of trisomy that was diagnosed.

• Short stature.

• Having a flat profile and a round face.

• Slanted eyes.

• Cleft palate.

• Abnormally developing or functioning organs (heart, lungs, or kidney).

• Intellectual disabilities and developmental delays.

How Is Trisomy Diagnosed?

Early trisomy diagnosis during pregnancy is facilitated by genetic testing. The diagnosis is confirmed soon after birth, following a physical examination and additional genetic chromosome testing on the newborn using a blood sample.

In addition to an ultrasound, the healthcare provider will offer screening tests during pregnancy to analyze a sample of the birthing parent's blood. The doctor will check the ultrasound for trisomy symptoms like extra amniotic fluid, nuchal lucency (fluid under the skin behind the neck), and abnormal limb lengths. These might indicate a genetic anomaly.

Additional tests help confirm the diagnosis after a screening, such as:

• Chorionic Villus Sampling (CVS): The healthcare provider will take a small sample of cells from the placenta of the mother between 10 and 13 weeks of pregnancy to check for genetic disorders and the gender of the unborn child.

• Amniocentesis: The healthcare provider will take a tiny sample of amniotic fluid between 15 and 20 weeks of pregnancy to check for any potential health issues in the unborn child.

• Percutaneous Umbilical Blood Sampling (PUBS): To check for health issues in the baby, the healthcare provider will take a small sample of blood from the umbilical cord.

• Noninvasive Prenatal Testing: The doctor will examine a sample of the mother's blood after ten weeks of pregnancy to determine whether or not the child has any genetic abnormalities.

How Are Trisomy Conditions Treated?

Trisomy is a chronic condition that necessitates ongoing care to manage any symptoms. Children with trisomy receive the following types of care:

• Surgery to correct any physical abnormalities.

• Educational support.

• Physical, behavioral, and speech therapy.

• Medications to treat lingering symptoms of afflicted medical conditions.

Conclusion

As trisomy conditions and other genetic abnormalities cannot be prevented, if one intends to become pregnant, a healthcare provider must be consulted about genetic testing to determine the risk of passing on a genetic condition to the unborn child. There is support and medical care available to help the mother and the baby live healthy and fulfilling lives even if the child is diagnosed with a trisomy.