Down syndrome and Genetics

Down syndrome is one of the most common disorders in children, with more than 200,000 children worldwide born annually with Down syndrome.
There are many causes of Down syndrome, including genetic and environmental factors, but so far there is no known specific cause for the syndrome.

Is Down Syndrome considered hereditary, that is, transmitted from parents to children? What is the importance of genetic testing in early diagnosis of Down syndrome and determining appropriate rehabilitation treatment for the child to develop his physical, mental and social skills?

In this article, we will shed light on the causes and types of Down Syndrome, the importance of genetic testing in early diagnosis, and changing rehabilitation treatment methods.

Down syndrome

Down Syndrome is one of the genetic disorders that occurs due to abnormal cell division during the formation of the fetus, which results in an extra copy of chromosome 21, so that the child has 47 chromosomes instead of 46 chromosomes.
The severity of Down syndrome varies from one child to another and results in intellectual disability, delayed growth, and learning difficulties, in addition to speech problems.

Symptoms of Down syndrome

Children with Down syndrome often share many physical features, the most notable of which are:

• A flattened face
• Short stature
• Muscle weakness
• Unusually shaped or small ears
• Short neck
• The presence of small white spots in the iris
• Relatively short fingers and small hands and feet

Types of Down syndrome

The types of Down syndrome vary according to the number of extra copies of chromosomes, and are classified into 3 main types:

Trisomy 21

Trisomy 21 is the most common type of Down syndrome, as 95% of Down syndrome cases are trisomy 21. In this type, there are 3 copies of chromosome 21 in each cell of the body instead of two copies.

Translocation Down syndrome

This type represents approximately 3% of the total number of Down syndrome cases. In this type, there is one extra copy of chromosome 21 but it is usually attached to another chromosome.

Mosaic Down syndrome

This type is considered the least common type of Down syndrome, and its rate is only 2% of the total number of Down syndrome cases. This type is known as mosaicism due to a difference in the number of copies of chromosome 21, as some cells contain 3 copies of chromosome 21, while others contain 2 copies of chromosome 21. In this type of Down syndrome, the complications of the syndrome are relatively few, with the same physical features known for Syndrome.

Complications of Down syndrome

Down syndrome may result in many other health problems, the most important of which are:

• Congenital heart problems, the probability of developing which increases by 50%
• Sleep apnea, the risk of developing which increases by 50-79%.
• Hearing problems and the probability of infection, increases by 75%
• Eye-related issues, such as cataracts, the probability of developing which increases by 60%
• Nervous system disorders, the probability of developing increases by 1-13%.
• Immune disorders
• Obesity
• Abnormalities in the digestive system

Does Down syndrome run in families?

Although down syndrome is caused by a genetic abnormality, it is not often passed down from parents to their offspring. About 1% of cases of Down syndrome are inherited from parents to offspring, and the majority of these cases are trisomy 21, a condition in which each of the body's cells has three extra copies of chromosome 21.

Diagnosis of Down syndrome

Pregnancy-related Down syndrome can be diagnosed using one of two types of tests:

Screening tests

This kind of test involves blood work and ultrasound pictures of the developing fetus to measure the volume of fluid behind its neck. A large volume of fluid behind the fetus's neck is thought to be a sign of a genetic abnormality, which needs to be confirmed by additional testing.

Diagnostic tests

This type of test is recommended after a positive screening tests to confirm the diagnosis of Down Syndrome, including:

• Amniocentesis - examining the amount of fluid surrounding the fetus.
• Chorionic villus sampling (CVS) - examines placenta cells.
• Percutaneous umbilical blood sampling (PUBS) - examines blood from the umbilical cord.

The importance of genetic testing in the early diagnosis of Down syndrome

Karyotyping

Down syndrome can also be diagnosed after birth through Karyotyping, which examines defects in the number and shape of chromosomes in the body's cells to diagnose Down syndrome and some other genetic diseases, such as Patau syndrome, Klinefelter syndrome, and Turner syndrome, in addition to its importance for couples who suffer from infertility or Recurrent miscarriage.

Noninvasive Prenatal test (NIPT)

The abbreviation NIPT refers to non-invasive prenatal test, which is an genetic screening that is performed by drawing a blood sample from the arm of the pregnant mother that contains some fetal DNA to determine the sex of the fetus and ensure its safety from genetic syndromes resulting from a defect in the number of chromosomes, such as : Down Syndrome, Patau Syndrome, and Edwards Syndrome.

Related article: Noninvasive Prenatal Test (NIPT) and what to expect

Genetic counseling

Genetic counseling helps guide the appropriate procedure and recommend a more comprehensive genetic testing based on the information provided about the health condition of you and your family. Genetic counseling also contributes to determining the frequency of Down syndrome in the family based on the degree of kinship and the extent of the prevalence of genetic diseases.

The role of the genetic counselor is not only limited to the pre-test stage, but also helps you understand the results of the test in order to give you the necessary recommendations and directions and provide you with the necessary support.

Enigma Genomics provides comprehensive genetic tests for hereditary diseases, such as premarital screening, which covers more than 550 hereditary diseases, Non-Invasive Prenatal Test (NIPT), Karyotyping, Whole Genome Sequencing, which covers more than 7,500, and Whole Exome Sequencing, which covers 7,000 genetic diseases and others, in addition to tele genetic counseling service to help you in the journey of maintaining your health and the health of your family.