Hereditary diseases, also known as inherited diseases or genetic disorders, are diseases that are passed on from one generation to another through defective genes. These diseases are transmitted in the same family. In some cases, one generation of the family may only be the carrier of the defective gene and the next generation may get affected by the disease. The chromosomes in humans are responsible for passing the traits from the parent to the offspring. There are thousands of genes on the pair of chromosomes, X and Y, and each gene carries a trait. Usually genes carry normal traits but sometimes due to reasons unknown, the genes get altered resulting in a 'mutant' gene. The offspring inherits a copy of gene from each parent and if either one or both the copies of gene are mutated, then the offspring is at a risk of getting an inherited disease. Most of the time, parents are unaware that they are suffering from a particular disease and have passed on the defective gene to the child unless the child is afflicted.

List of Hereditary Diseases

There are numerous genetic diseases and disorders that are passed from the parent to the offspring. Some of these diseases may be congenital (present at the time of birth) or can even occur after a while. There are some other inherited diseases where the females are just the carriers of the defective genes and pass on to the male members of the family. Genetic diseases usually fall into four categories which are given below:

Autosomal Dominant Diseases
There is a specific pattern of inheritance of genes in autosomal dominant diseases. The offspring inherits a copy of normal gene and mutant gene from its parents. Either of the parents may often suffer from a disease and thus the abnormal gene is passed on to the child. The abnormal or faulty gene tends to dominate the normal gene and the child has a 50 percent chance of inheriting the disease. Sometimes the child does not inherit the abnormal gene or develop the disease. Some such examples of autosomal dominant diseases are given below:

It is a genetic disorder in humans which leads to stunted growth or dwarfism. Individuals suffering from this disorder have disproportionate and short limbs. They also have a stunted structure, growing not more than 4 feet. The main causative factor for this condition is the mutation of the FGFR3 gene which is located in the fourth chromosome. However, there is no treatment for this condition.

Hereditary Hemochromatosis
Hereditary hemochromatosis is another condition which leads to over absorption of iron in the intestine. Since excess iron cannot be eliminated from the body, it tends to accumulate in the intestine and damage the nearby organs like the liver and from there, spread to the heart. The symptoms of this disorder are loss of memory, impotence, muscle cramps and severe joint pain.

Down Syndrome
Down syndrome, which is caused due to an extra copy of chromosome 21 is an autosomal dominant disease. This disorder also known as Trisomy 21 is characterized by a round face, narrow chin and bulging eyes. This condition is rare and is seen in 1 among 1000 children. However, the severity of this disorder can be controlled if it is diagnosed when the child is in the womb.

Hereditary Spherocytosis
In hereditary spherocytosis, the red blood cells or erythrocytes are produced in an abnormal shape due to which the cell membrane gets ruptured. The damage of the erythrocytes results in hemolytic anemia. This condition shows symptoms like increased fatigue, paleness of the skin and jaundice. Other diseases in this category include Jackson Weiss Syndrome, Huntington's disease and galactosemia.

Autosomal Recessive Diseases
These diseases occur when both the parents carry a defective trait in their genes, which is then passed on to the offspring. The defective gene is usually transferred during the process of fertilization. The chances of the child developing the disease is 25 percent if both the parents are carriers of the defective gene. Some examples are given below:

Tay-Sachs Disease
One autosomal recessive disease is the Tay-Sachs disease, which affects the nervous system, and leads to the loss of motor skills. The symptoms of this disease include delayed growth, dementia, irritability and sometimes even paralysis. Unfortunately, there is no treatment available to cure this disorder and children affected by this disease don't live longer than five years of age.

Polycystic Kidney Disease
Polycystic kidney disease is another rare condition which affects 1 out of 2,00,000 people. In this condition, numerous cysts form on the kidneys, which may lead to kidney failure. The individual suffering from this disorder will display symptoms like frequent urination as a result of increased amount of urine in the body, enlarged spleen, bleeding in the gastrointestinal tract and high blood pressure.

Usher Syndrome
Usher Syndrome is also a type of autosomal recessive disease which is a result of a faulty gene. This syndrome is categorized into three types which can be seen in different age groups - type 1, type 2 and type 3. In type 1, the sufferers are congenitally deaf or sometimes they become deaf when they are a year old. Type 2 patients are born deaf and experience loss of vision during the teens or early adulthood. Individuals having type 3 syndrome tend to lose both the power of vision and hearing when they are 10 years of age. Sadly, a cure for this syndrome has not yet been discovered.

Hereditary Fructose Intolerance
Hereditary fructose intolerance is yet another disorder where the individual lacks the enzyme, aldolase B, which is required for the breakdown of the fructose molecules. This disorder can lead to serious health hazards if not diagnosed in time. The symptoms observed are severe abdominal pain, vomiting, dislike for sweet foods, irritation after eating foods rich in fructose, etc. Other examples are sickle cell anemia, albinism, cystic fibrosis and phenylketonuria.

Gender Linked Diseases
There are two sex chromosomes, X and Y, in the genes. Human males have an X and Y chromosome (i.e XY) , whereas in females both the chromosomes are X (i.e XX). Gender or sex related diseases are attributed to either of the sex chromosome. In the X linked dominant disorder, the father passes on the defective gene to his daughters but not to his sons. In case the mother carries the faulty X gene, both the sons and daughters are liable to inherit the disease. Some examples are given below:

Color Blindness
Color blindness is a result of the mutated X chromosome. This can result in the damage to the nerve, eye and sometimes even the brain and the individual suffering from this disorder is unable to differentiate between colors. However for correction of this disorder, special types of contact lenses and tinted filters prescribed by an ophthalmologist may enable the individual to tell the difference between colors.

Hemophilia is a blood related disorder where the blood in the affected individuals loses the ability to coagulate or clot. This condition is passed on from the father to the daughters in the X chromosome where she is only the carrier of the defective gene. She in turn passes this disorder to her sons who become sufferers as they have the defective X chromosome and normal Y chromosome. In some rare cases, females also tend to suffer from hemophilia. This disease is also known as bleeder's disease.

Muscular Dystrophy
Muscular dystrophy is a group of genetically inherited muscle disorders which results in the wasting of the muscles. This condition is characterized by weakness in the skeletal muscles, degeneration of the cells and tissues in the muscles and defective muscle proteins. Some of the symptoms are observed during childhood, while some symptoms make an appearance in early adulthood. Certain therapies like speech therapy, respiratory therapy and orthopedic surgery are adopted to correct this disorder.

Polygenic Disorders
Polygenic disorders occur due to the influence of multiple genes. Though the disorders under this condition are not completely inherited, they may have a slight family inheritance. The main risk factor in this disorder is a family history of these diseases. These diseases are also influenced by environmental factors. The examples of this kind of disorder are diabetes, breast cancer, coronary heart diseases, obesity and autoimmune diseases.

A Few Other Genetic Disorders

Apart from the above mentioned diseases that affect humans, there are several chromosomal disorders that are a still a mystery to doctors worldwide. These diseases are still being researched upon, in the hope of a breakthrough regarding their cause and cure. Some other hereditary diseases in humans which are rare and incurable are as follows:
  • Acid Maltase Deficiency
  • Albinism
  • Angelman Syndrome
  • Canavan Disease
  • Charcot-Marie-Tooth Disease
  • Cri du Chat Syndrome
  • Duchenne Muscular Dystrophy
  • Fragile X Syndrome
  • Galactosemia
  • Gilbert's Syndrome
  • Joubert Syndrome
  • Klinefelter Syndrome
  • Krabbe Disease
  • Lesch-Nyhan Syndrome
  • Marfan Syndrome
  • Myotonic Dystrophy
  • Nail-Patella Syndrome
  • Neurofibromatosis
  • Noonan Syndrome
  • Pelizaeus-Merzbacher Disease
  • Phenylketonuria
  • Porphyria
  • Prader-Willi Syndrome
  • Prune Belly Syndrome
  • Retinoblastoma
  • Rett Syndrome
  • Rubinstein-Taybi Syndrome
  • Russell Silver Syndrome
  • Sanfilippo Syndrome
  • Shwachman Syndrome
  • Spina bifida
  • Smith-Magenis Syndrome
  • Stickler Syndrome
  • TAR Syndrome
  • Tay-Sachs Syndrome
  • Turner Syndrome
  • Usher Syndrome
  • Variegate Porphyria
  • Von Hippel-Lindau Syndrome
  • Waardenburg Syndrome
  • Wilson's Disease
  • Wolf-Hirschhorn Syndrome
  • Xeroderma Pigmentosum
  • XXXX Syndrome
  • XXX Syndrome
  • XYY Syndrome
  • YY Syndrome
These genetic disorders cannot be avoided completely. However thanks to the development of medical science, they can be detected in the womb and their severity can be decreased to an extent. There are also many improved treatment options that help control the intensity of the disease.