GENETIC DISEASES

WHAT ARE GENETICS?

GENETICS, THE SCIENCE OF GENES & HEREDITY

Genetics is the study of genes particularly and of heredity primarily. Genetics arose out of the identification of genes, the fundamental units responsible for heredity. Genetics may be defined as the study of genes at all levels, including the ways in which they act in the cell and the ways in which they are transmitted from parents to their offspring.

Genes are the building blocks of heredity. They are passed from parents to their children. They hold DNA, the instructions for making proteins. Proteins do most of the work in cells, including:

  Breaking Down Toxins
  Building Structures
  Moving Molecules From Place To Place
  Other Maintenance Jobs

Heredity is a biological process where a parent passes certain genes onto their children / offspring. Every child inherits genes from both of their biological parents, and these genes in turn express specific traits. Some of these traits may be physical, such as eye color, hair color, or skin color. On the other hand, some genes may also carry the risk of certain diseases and disorders that may pass on from parents to their offspring.

WHAT IS A GENETIC DISEASE?

GENETIC DISEASE, THE RESULT OF A GENETIC MUTATION

Sometimes, there is a change in a gene or genes: a genetic mutation. The mutation changes the gene’s instructions for making a protein, so the protein does not work properly or is missing entirely. This can cause a medical condition called a genetic disease.

A genetic disease is any disease or disorder caused by an abnormality in the genetic makeup of an individual. The genetic abnormality can range from major to minuscule – from a chromosomal abnormality of gross proportions, involving the addition or subtraction of an entire chromosome or set of chromosomes, to a discrete mutation in a single base in the DNA of a single gene. Some people inherit genetic disorders from their parents, while acquired changes, or mutations in a preexisting gene or group of genes, cause other genetic diseases. Genetic mutations can occur either at random or due to some environmental exposure.

FOUR TYPES OF INHERITED GENETIC DISORDERS

There are four different types of inherited genetic disorders:

1.  CHROMOSOME ABNORMALITIES

2.  MITOCHONDRIAL INHERITANCE

3.  MULTIFACTORIAL INHERITANCE

4.  SINGLE GENE INHERITANCE

COMMON GENETIC DISEASES

CHROMOSOME ABNORMALITIES

Chromosomes, distinct structures consisting of DNA and protein, are found in the nucleus of each cell. Because chromosomes are the carriers of our body’s genetic material, abnormalities in their number or structure can result in disease. Typically, a chromosomal abnormality occurs due to an issue with cell division.

For example, Down syndrome (occasionally referred to as “Down’s syndrome”) or trisomy 21, is a common genetic disorder that arises when an individual has three copies of chromosome 21. There are many other chromosome abnormalities, including:

  Cri du chat syndrome, or the “call of the cat” syndrome (46 XX / 46 XY, 5p-).
  Klinefelter syndrome (47, XXY).
  Turner syndrome (45, X0).

Diseases may also occur because of chromosomal translocation in which portions of two chromosomes are exchanged.

MITOCHONDRIAL INHERITANCE

This type of genetic disease is caused by mutations in the non-nuclear DNA of mitochondria. Mitochondria are found in the cytoplasm of animal and plant cells and are miniscule, rod-like or round organelles that are involved in cellular respiration. Each mitochondrion may contain five to ten circular pieces of DNA. Since egg cells, but not sperm cells, retain their mitochondria during fertilization, mitochondrial DNA is always inherited from the mother.

Examples of mitochondrial inheritance include:

  Leber’s hereditary optic neuropathy (LHON), an eye disease.
  Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome, a rare form of dementia.
  Myoclonic epilepsy with ragged red fibers (MERRF) syndrome.

MULTIFACTORIAL INHERITANCE

Multifactorial inheritance is also called complex or polygenic inheritance. Multifactorial inheritance disorders are caused by a combination of environmental factors and mutations in multiple genes. For example, different genes that influence susceptibility to breast cancer have been found on chromosomes 6, 11, 13, 14, 15, 17, and 22. Some common chronic diseases are also multifactorial inheritance disorders.

Additional examples of multifactorial inheritance include:

  Alzheimer’s Disease
  Arthritis
  Cancer
  Diabetes
  Heart Disease
  High Blood Pressure
  Obesity

Furthermore, multifactorial inheritance is associated with heritable traits, such as eye color, fingerprint patterns, height, and skin color.

SINGLE GENE INHERITANCE

Single gene inheritance is also called Mendelian or monogenetic inheritance. Changes or mutations that occur in the DNA sequence of a single gene allow for this type of inheritance. Presently, there are thousands of known single gene disorders. These disorders are referred to as monogenetic disorders; disorders of a single gene.

Single gene disorders have distinct patterns of genetic inheritance, including:

  Autosomal dominant inheritance, in which just one copy of a defective gene (from either parent) is required to cause the condition.
  Autosomal recessive inheritance, in which two copies of a defective gene (one from each parent) are required to cause the condition.
  X-linked inheritance, in which the defective gene is located within the female, or X-chromosome. X-linked inheritance can be either dominant or recessive.

Some examples of single gene inheritance include:

  Alpha-Thalassemias
  Beta-Thalassemias
  Cystic Fibrosis
  Fragile X Syndrome
  Hemochromatosis
  Huntington’s Disease
  Marfan Syndrome
  Sickle Cell Anemia (Sickle Cell Disease)

THE FUTURE OF GENETIC DISEASES

INVESTIGATING & RESEARCHING THE HUMAN GENOME

The human genome is the entire inheritance of an individual’s genes. The sequence of the human genome provides the first holistic look at our genetic heritage. Between the 46 human chromosomes, which includes 22 pairs of autosomal chromosomes and two sex chromosomes, almost three billion base pairs of DNA are housed, which all contain about 20,500 protein-coding genes. Some chromosomes have a higher density of genes than others, and the coding regions make up less than five percent of the human genome. The function of all the remaining DNA is still unclear.

Most genetic diseases are the direct result of a mutation in a single gene. However, one of the most difficult problems ahead is to better explain and further understand how genes contribute to diseases that have a complex pattern of inheritance, such as in the cases of asthma, cancer, diabetes, and mental illness. In all these cases, no gene has the exclusive power to answer “no” or “yes” on whether an individual will develop the disease or not. It is likely that a number of genes may each play an important, yet subtle role in a person’s susceptibility to a disease, and that more than one mutation is required before the disorder can manifest; genes may also affect how a person reacts to environmental factors.

IMPORTANT! All information presented in this website is intended for informational purposes only and not for the purpose of rendering medical advice. Statements made on this website have not been evaluated by the Food and Drug Administration. The information contained herein is not intended to diagnose, treat, cure or prevent any disease.