Enfermedades Hereditarias

INTRODUCTION

Human Genetic Disease, any of the diseases and disorders that are caused by mutations in one or more genes.

With the increasing ability to control infectious and nutritional diseases in developed countries, there has come the realization that genetic diseases are a major cause of disability, death, and human tragedy. Rare, indeed, is the family that is entirely free of any known genetic disorder. Many thousands of different genetic disorders with defined clinical symptoms have been identified. Of the 3 to 6 percent of newborns with a recognized birth defect, at least half involve a predominantly genetic contribution. Furthermore, genetic defects are the major known cause of pregnancy loss in developed nations, and almost half of all spontaneous abortions (miscarriages) involve a chromosomally abnormal fetus. About 30 percent of all postnatal infant mortality in developed countries is due to genetic disease; 30 percent of pediatric and 10 percent of adult hospital admissions can be traced to a predominantly genetic cause. Finally, medical investigators estimate that genetic defects—however minor—are present in at least 10 percent of all adults. Thus, these are not rare events.

Human Genetic Disorders

Genetic disorders are classified into Chromosomal. Single-genic, Polygenic and Mitochondrial disorders

Both environmental and genetic factors have roles in the development of any disease. However there are several genetic disorders caused exclusively by anomalies in the genetic material of an individual.

Genetic disorders are classified into the following:

1. Chromosomal Disorders- Chromosomes, which are distinct structures made up and protein, are located in the nucleus of each cell. Abnormalities in the chromosome structure or number results in a disease. Several chromosomal abnormalities can be detected by microscopic examination. Down syndrome or trisomy 21, a classical example, is a common disorder that occurs due do the presence of three copies of chromosome 21.

2. Single-gene disorders - Also called Mendelian or monogenic disorders. Mutations that occur in the DNA sequence of a single gene give rise to these disorders. They occur in about 1 out of every 200 births, and have a specific pattern of inheritance such as autosomal dominant, autosomal recessive and X-linked. There are more than 6,000 known single-gene disorders and some of the famed examples are cystic fibrosis, Huntington’s disease, Marfan syndrome and sickle cell anemia.

3. Multifactorial or polygenic Disorders - These disorders are caused by a combination of mutational changes on an array of genes and environmental factors.. Its complexity makes it more difficult to analyze multifactorial disorders. Examples include cancer, diabetes, heart disease, obesity, high blood pressure, Alzheimer’s disease and arthritis. Several mutational changes in the BRCA genes that increase the risk of developing breast cancer have been discovered.

4. Mitochondrial Disorder - These rare type of genetic disorders arise from changes in the DNA of mitochondria which are organelles found in the cytoplasm of plant and animal cells, responsible for cellular respiration. Each mitochondrion may contain 5 - 10 circular pieces of DNA and are usually passed on from the mother to the offspring.

Cause of Genetic Disorders:

A genetic disorder is an abnormal condition that a person inherits through genes or chromosomes. Some genetic disorders are caused by mutations in the DNA of genes. Other disorders are caused by changes in the overall structure or number of

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