Disabilities and Genetics
The term "disability" in its conventional sense refers to a disorder resulting from health problems or environmental factors that affects a specific organ in the body, such as mental disability, motor disability, disabilities affecting growth, and visual and hearing disabilities.
Approximately 16% of people worldwide face one or more types of disabilities, and the percentage is still rising, according to the most recent statistics from the World Health Organization. This exposes them to the possibility of complications and other health problems like diabetes and obesity, as well as psychological problems such as depression, twice as much.
However, we find that the rates of severe disabilities in the Kingdom of Saudi Arabia amount to 2.9%, and visual disabilities rank first at 46.02% of the total population in Saudi Arabia who have one disability, followed by motor difficulties at 29.13% of the total population in Saudi Arabia who have more than one disability. While first-degree consanguineous marriage contributes to an increase in disability rates by about 3.5%.
What is the reason for the continuous increase in the rate of disabilities globally and in our Saudi society? To what extent do genes contribute to disabilities? Can it be detected and prevented early?
In this article, we will reformulate the concept of disability from a genetics perspective and highlight the importance of genetic testing in discovering the genetic factors that cause disabilities and the extent of its impact on changing the lives of individuals and families.
Disabilities and Genetics
Genetic factors play a major role in some disabilities, including:
Neurodevelopmental developmental disorders (NDD)
Neurodevelopmental developmental disorders affect approximately 15% of children and adults worldwide. They are disorders that affect the efficiency of the brain and nervous system and include:
1. Autism spectrum disorders: Genetic factors increase the chances of having a child with autism by 40-80%, such as having relatives with autism, Down syndrome, or fragile X syndrome.
The likelihood of having another child with autism also increases by 10-20%, and males are 4 times more likely to develop autism than females. If the baby is a Siamese twin (conjoined twin), the probability of developing autism increases to 59%.
At the level of relatives, the probability of recurrence of autism varies depending on the degree of relationship as follows:
- The probability of a cousin developing autism increases by 3%.
- The probability of infection for half-siblings on the father's side increases by 7%, and 9% for half-siblings on the mother's side.
- The probability of full siblings being infected increases by 19%.
2. Intellectual disabilities: Genetic factors increase the chances of mental disabilities occurring by more than 80%, examples of which include Down syndrome, fragile X syndrome, and others.
3. Epilepsy: Genetic factors contribute to about 70% of epilepsy cases, and the chances of recurrence of epilepsy increase by 2-10 times if there are parents with it. Some genetic syndromes also increase the chances of epilepsy, such as fragile X syndrome, Rett syndrome, and tuberous sclerosis. In addition, researchers have discovered 84 genes so far related to epilepsy and 73 genes that are associated with brain abnormalities and may have a role in epilepsy as well. Examples of these genes include: the SCN1A gene and the TSC1 and TSC2 genes
Hearing disabilities
Genetic factors cause about 50-60% of cases of deafness in children, but it should be noted that 30% of the genetic changes that cause deafness are the result of hereditary syndromes that increase the chances of developing deafness, and 70% of these changes are not linked to any hereditary syndromes.
So far, researchers have discovered more than 70 genes that increase the chances of children becoming deaf, even if both parents are healthy. The most prominent of these genes are:
BDP1, CDH23, EPS8L2, and GJB2 genes responsible for producing the protein for cochlear formation, LOXHD1, MYO7A, PCDH15, and SLC26A4.
Visual impairments
More than 260 genes contribute to blindness and hereditary retinal diseases, including ACP6, AMOT, ARHGEF10L, ATP6V1A, DCAF6, DLG4, GABRB2, GRIN1, GRIN2B, KCNQ3, KCTD19, RERE, and SLC1A1 genes.
The chances of developing hereditary syndromes that cause vision loss also increase as a result of having affected relatives. Examples of these diseases that affect vision include:
Age-related macular degeneration (AMD)
a disease that affects the central vision center in the retina and is called the “macula,” causing complete loss of vision at age 50 and older. In 15-20% of cases, the causes of macular degeneration are due to the presence of one or more first-degree relatives (parents or siblings) with this condition.
Glaucoma
Glaucoma results from damage to the optic nerve connected to the brain, leading to vision loss. Glaucoma is usually diagnosed in the late stages and more than 50% of undiagnosed glaucoma cases are likely to have genetic causes.
Cataracts
This is a condition that affects the lens of the eye, causing blurred and distorted vision, sensitivity to intense light, and poor vision at night. Other complications may result if left untreated. One in five cases of cataracts are due to having close relatives with the condition, and some genetic syndromes can also contribute to an increased chance of developing cataracts, such as Down syndrome.
The importance of genetic testing in diagnosing disabilities
Early diagnosis
Genetic testing helps identify the genetic causes of disabilities early through genetic screening before marriage and pregnancy, NIPT screening, and postnatal genetic testing to provide the necessary recommendations and accurately diagnose incurable cases early to provide the necessary care.
Helping in reproductive decisions
Genetic testing helps couples and married couples to discover genetic changes that may cause disabilities for their children in the future, such as hereditary deafness, hereditary blindness, learning difficulties, and others, in order to provide the necessary recommendations and available options for procreation.
Developing new treatments
Gene therapy, thanks to genetic testing, has contributed to the development of a new treatment for hereditary blindness approved by the US Food and Drug Administration, which is based on introducing a copy of the RPE65 gene into the patient's eye through a viral vector to restore eye efficiency.
Discovering genes-cause disabilities
Genetic testing contributes to discovering more genes that cause disabilities to ensure accurate diagnosis and develop appropriate treatments.
Genetic counseling helps individuals and families nominate appropriate genetic testing according to health status and family history of genetic diseases and provides the necessary support.
Enigma Genomics provides virtual genetic counseling and comprehensive genetic screening to reduce the spread of genetic diseases and provide a better life for individuals and families.