Genetic Disorders – An Overview

Introduction

A genetic disorder is a disease that occurs in whole or in part due to a change in the DNA sequence from normal. The cause behind genetic disorders could be abnormality during cell formation and development or any environmental influence.

Genetic disorders 

Genetic disorders include mutations in one gene (single genetic disorders), mutations in multiple genes (multifactorial genetic disorders), a combination of genetic mutations and environmental factors or damage to chromosomes (changes in the number of the whole chromosome, structure carrying genes).

By discovering the secrets of the human genome (the complete set of human genes), we learn that almost every disease has a genetic component. Some diseases, such as sickle cell disease, are caused by inherited mutations and are present at birth. Other diseases are caused by acquired mutations in a gene or group of genes during a person’s lifetime. These mutations are not inherited from parents but occur accidentally or due to environmental influences. These include several types of cancer and some forms of neurofibromatosis.

Types of Genetic Disorders

• Albinism

Albinism is a group of genetic conditions with little or no melanin pigment in the skin, hair, and eyes. Some symptoms include very pale skin, hair, eyes, patches of missing pigment, and crossed eyes.

People with albinism need to protect their skin and eyes from the sun and check their eyes regularly. The gene for albinism is inherited from two parents who cannot be affected by the disease.  

• Apert Syndrome

Apert Syndrome is a genetic disorder. Usually, neither parent develops the disease, nor gene mutations are accidental. A mutation usually present at birth causes the skull bones to heal much faster than usual before the brain fully grows. As the brain grows and pressure is applied, the bones of the head and face get deformed. Some symptoms include having a misshapen skull and a prominent forehead, underdeveloped upper jaw, and prominent eyes that appear to be bulging out.

• Ankylosing spondylitis

A type of arthritis that affects the joints and ligaments of the spine is called Ankylosing Spondylitis. In addition, other large joints may be affected and may be related to eye, skin, intestinal, and heart problems. Some symptoms include lower back pain and stiffness, hip pain, joint pain, and neck pain. To date, there is no cure found for Ankylosing spondylitis, but treatment can relieve pain and other symptoms.

• Angelman Syndrome 

Angelman Syndrome is a very rare genetic disorder. Most people with Angelman Syndrome do not have a missing gene called UBE3A. When this gene is defective or absent, nerve cells in the brain cannot function properly, causing various physical and intellectual problems. Some commonly seen symptoms include developmental delays, intellectual disability, no speech, etc. 

• Charcot-Marie-Tooth disease

A hereditary nervous system disorder called Charcot-Marie-Tooth (CMT) causes muscle problems in the feet, legs, arms, and hands. There is currently no cure available for CMT, but people with this disease can resort to various treatments and strategies to manage their symptoms. CMT diseases (also called hereditary motor and sensory neuropathy) are not separate diseases but genetic conditions that affect the nervous system. Some symptoms observed in people with this disease are weakness in legs, ankles, and feet, loss of muscle bulk in your legs and feet, high foot arches, and curled toes.

• Congenital adrenal hyperplasia

A congenital adrenal hyperplasia (CAH) is a group of hereditary disorders that affect the adrenal glands. These glands, located above the kidneys, release hormones such as cortisol, aldosterone (which helps regulate salt levels in the body), and androgens (male sex hormones). In many cases, people with CAH produce too many androgens and not enough cortisol and aldosterone. Some common symptoms are early signs of puberty, acne, irregular menstrual periods in females, etc.

CAH can affect normal growth and development in children, including normal growth of the genitals.

Types of Chromosomal Disorders

• Klinefelter Syndrome

These children are always boys and have XXY or XXXY sex chromosomes instead of a pair of XY chromosomes. Klinefelter Syndrome is not usually diagnosed in boys until puberty. Features of this condition include infertility, testicular contractions, and breast development. Mental retardation occurs occasionally but is not usually associated with Klinefelter Syndrome. A child’s testosterone levels are measured around 11 or 12 years of age. 

• Down Syndrome

Trisomy 21 is detected when an extra chromosome 21 is present. This causes a condition called Down Syndrome. Blood and ultrasound tests can now be used early in pregnancy to assess a mother’s risk of giving birth to a baby with Down Syndrome. The main problems are general developmental delays and mental retardation.  

• Edwards’ Syndrome

Trisomy 18, also called Edwards’ Syndrome, is a rare chromosomal abnormality. People with Edwards’ Syndrome have low birth weight and have fear of crying and sounds. They have feeding problems and cannot develop normally. They have a small head size with a prominent nape. Their ears are usually set low. Some develop seizures, kidney problems, and scoliosis (curvature of the spine) in the first year of life. Feeding problems, heart problems, and increased susceptibility to infections are contributing factors to the death of these children.

• Patau Syndrome

Patau Syndrome is a chromosomal defect in which an extra genetic code from chromosome 13 is found in all or some of the body’s cells. The extra genetic material interferes with normal development, resulting in various organ defects. The risk of this disorder in the offspring tends to increase with older mothers at pregnancy, as it does with all nondisjunction conditions. Trisomy 13 causes Patau Syndrome, which means that each cell in the human body has three copies of chromosome 13 rather than the usual two. The majority of Patau Syndrome cases are not inherited and occur due to random events during the development of reproductive cells.

• Turner Syndrome

Turner Syndrome (TS) is a genetic disorder in which a woman misses an X chromosome partially or completely. Short and webbed necks, low-set ears, a reduced hairline at the nape of the neck, small stature, and swollen feet and hands are all common birth characteristics. Without hormone treatment, those affected usually do not develop menstrual periods or breasts, and they are incapable of having children without reproductive technology. Heart defects, diabetes, and poor thyroid hormone production are common in this disorder. Turner Syndrome is rarely inherited; instead, it develops during the formation of a parent’s germ cells or early cellular division during development.  

• Type 1 Oculocutaneous Albinism

Skin complexion albinism is a group of conditions that affect the colour (pigmentation) of the skin, hair, and eyes. Affected people usually have very light skin and white or blonde hair. Long-term sun exposure significantly increases the risk of skin cancer, and skin damage, including an aggressive form of skin cancer, called melanoma.  People with this condition usually have vision problems, such as decreased sharpness, rapid involuntary eye movements (nystagmus), and increased photosensitivity (photophobia).  

Conclusion

The cause of genetic disorders discussed could be abnormality during cell formation and development or any environmental influence. It’s recommended that anyone with a family history of genetic disorders gets tested to understand his/her risk and how he/she can protect his/her health. Usually, genetic disorders can be classified as single-gene disorders, chromosomal disorders, and complex disorders depending on the cause.