The combinations create codes for different genes. Each person has about 20, genes. The genes code for different traits, such as eye color, body type, or male or female sex.
Inside each cell, DNA is tightly wrapped together in structures called chromosomes. Every normal cell has 23 pairs of chromosomes for a total of 46 :. To form a fetus, an egg from the mother and sperm from the father come together. The egg and sperm each have one half of a set of chromosomes. The egg and sperm together give the baby the full set of chromosomes. Genetic disorders can be caused by a mutation in one gene monogenic disorder , by mutations in multiple genes multifactorial inheritance disorder , by a combination of gene mutations and environmental factors, or by damage to chromosomes changes in the number or structure of entire chromosomes, the structures that carry genes.
As we unlock the secrets of the human genome the complete set of human genes , we are learning that nearly all diseases have a genetic component. Some diseases are caused by mutations that are inherited from the parents and are present in an individual at birth, like sickle cell disease.
Other diseases are caused by acquired mutations in a gene or group of genes that occur during a person's life. Such mutations are not inherited from a parent, but occur either randomly or due to some environmental exposure such as cigarette smoke.
These include many cancers, as well as some forms of neurofibromatosis. This list of genetic, orphan and rare diseases is provided for informational purposes only and is by no means comprehensive.
Duchenne muscular dystrophy DMD, the commonest muscular dystrophy in kids, causes gradual loss of muscle function, affecting everyday activity. Read more about Duchenne muscular dystrophy. Ehlers-Danlos syndrome People with Ehlers-Danlos have very loose joints and easily bruised or stretchy skin. Read more about Ehlers-Danlos syndrome. Fragile X syndrome Fragile X causes intellectual disability, behavioural and learning difficulties, and physical problems.
Read more about Fragile X syndrome. Haemochromatosis Haemochromatosis causes the body to absorb too much iron, leading to organ damage. Read more about Haemochromatosis.
Haemophilia Haemophilia stops blood from clotting properly, causing abnormal bleeding. Read more about Haemophilia. Klinefelter syndrome Affecting males, symptoms can include small genitals and infertility. Read more about Klinefelter syndrome.
Marfan syndrome This condition affects tissue that strengthens and stabilises joints and muscles. Read more about Marfan syndrome. Neurofibromatosis Neurofibromatosis is a manageable genetic condition characterised by benign tumours. Read more about Neurofibromatosis.
Noonan syndrome Children with Noonan syndrome may have odd facial features, restricted growth and heart defects, but most, with therapy, go on to lead normal lives. Read more about Noonan syndrome. Prader-Willi syndrome Adults with Prader-Willi may experience sleeping and breathing problems, and have an insatiable appetite, which can lead to life-threatening obesity.
Read more about Prader-Willi syndrome. Rett syndrome Rett syndrome causes intellectual and physical disability. Read more about Rett syndrome. Read more about Tay-Sachs disease. Thalassaemia This inherited blood disorder prevents someone from making enough healthy haemoglobin to carry oxygen around the body, but it may not need treatment.
Our DNA provides the code for making proteins , the molecules that perform most of the functions in our body. However, when a section of our DNA is changed in some way, the protein it codes for is also affected and may no longer be able to carry out its normal function.
Depending on where these mutations occur, they can have little or no effect, or may profoundly alter the biology of cells in our body, resulting in a genetic disorder. Genetic disorders can be grouped into three main categories: 1. Dominant diseases: single gene disorders that occur when an individual has one altered copy of the relevant gene and one healthy copy. Recessive diseases: single gene disorders that only occur when an individual has two altered versions of the relevant gene.
For example, cystic fibrosis. X-linked disorders: single gene disorders that reflect the presence of an altered gene on the X chromosome. X-linked disorders are more common in males because they only have one X chromosome.
As a consequence males only need one copy of the altered gene for symptoms to occur. For example, muscular dystrophy. Related Content:.
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