Metabolic diseases
Background
Metabolic diseases are a group of more than one thousand inherited disorders in which there is genetic fault in metabolism (the body’s chemistry).
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Aarskog-Scott syndrome
Background
Aarskog syndrome: Aarskog-Scott syndrome
Aarskog syndrome is a rare inherited condition described in 1970 by Dr D Aarskog and Dr C I Scott in 1971. It is a development disorder characterised by short stature with facial, genital and skeletal anomalies. The condition affects mainly males, although females may have milder features. Aarskog syndrome is associated with a wide range of features and not all features of the syndrome will be found in each individual; it affects individuals differently. Read more…
XYY syndrome
Background
XYY syndrome is a chromosomal condition which occurs only in males and is found with a frequency of 1 in 1,000. A chromosome is a rod-like structure present in the nucleus of all body cells, with the exception of the red blood cells. Chromosomes store genetic information. Normally humans have twenty-three pairs of chromosomes, forty-six chromosomes in total. The twenty-thirdrd pair, otherwise referred to as the sex chromosomes, store genetic information which determine our sex. A female has a XX pair and a male has a XY pair of chromosomes.
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What is Cri-du-Chat syndrome?
The name of this syndrome is French for “cry of the cat,” referring to the distinctive cry of children with this disorder. The cry is caused by abnormal larynx development, one of the many symptoms associated with this disorder. It usually becomes less noticeable as the baby gets older, making it difficult for doctors to diagnose cri-du-chat after age two. Cri-du-chat is caused by a deletion (the length of which may vary) on the short arm of chromosome 5. Multiple genes are missing as a result of this deletion, and each may contribute to the symptoms of the disorder. One of the deleted genes known to be involved is TERT (telomerase reverse transcriptase). This gene is important during cell division because it helps to keep the tips of chromosomes (telomeres) in tact.
How do people get Cri-du-Chat syndrome? Read more…
What is Huntington’s Disease?
Huntington’s Disease (HD) is a brain disorder that affects a person’s ability to think, talk, and move.
The disease destroys cells in the basal ganglia, the part of the brain that controls movement, emotion, and cognitive ability. HD is caused by a mutation in a gene on chromosome 4. The job of its protein product, huntingtin, is to direct the delivery of small packages (vesicles containing important molecules) to the outside of the cell. Normally, the coding region of this gene contains the DNA sequence “CAG” repeated again and again. The number of times this triplet is repeated varies from person to person, ranging from 10 to 26 times. People with HD have an abnormally high number of these CAG triplets, approximately 40 or more. This likely disrupts the function of the gene’s protein product, but how the expansion of the CAG repeat causes disease is unknown. Somehow the brain cells of HD patients accumulate clumps of protein that become toxic, resulting in cell death. Some patients lose more than 25% of their brain cells before they die.
How do people get Huntington’s Disease? Read more…
What is Williams syndrome?
Williams syndrome is a rare genetic disorder that affects a child’s growth, physical appearance, and cognitive development. People who have Williams syndrome are missing genetic material from chromosome 7, including the gene elastin. This gene’s protein product gives blood vessels the stretchiness and strength required to withstand a lifetime of use. The elastin protein is made only during embryonic development and childhood, when blood vessels are formed. Because they lack the elastin protein, people with Williams Syndrome have disorders of the circulatory system and heart defects.
How do people get Williams syndrome?
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DOWN SYNDROME
What is Down syndrome?
Down syndrome is a developmental disorder caused by an extra copy of chromosome 21 (which is why the disorder is also called “trisomy 21″). Having an extra copy of this chromosome means that each gene may be producing more protein product than normal. Cells seem to tolerate this better than having not enough protein, or having altered protein due to a mutation in the DNA sequence. However, producing too much protein can also have serious consequences, as seen in Down syndrome. Genes on chromosome 21 that specifically contribute to the various symptoms of Down syndrome are now being identified.
How do people get Down syndrome?
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KLINEFELTER SYNDROME
What is Klinefelter syndrome?
Klinefelter syndrome is a disorder that affects only males. Males normally have an X chromosome and a Y chromosome (XY). But males who have Klinefelter syndrome have an extra X chromosome (XXY), giving them a total of 47 instead of the normal 46 chromosomes.
People with this disorder develop as males with subtle characteristics that become apparent during puberty. They are often tall and usually don’t develop secondary sex characteristics, such as facial hair or underarm and pubic hair. The extra X chromosome primarily affects the testes, which produce sperm and the male hormone testosterone. Read more…
TURNER SYNDROME
What is Turner syndrome?
Turner syndrome is caused by a missing or incomplete X chromosome. People who have Turner syndrome develop as females. The genes affected are involved in growth and sexual development, which is why girls with the disorder are shorter than normal and have abnormal sexual characteristics.
How do people get Turner syndrome? Read more…
Achondroplasia
Introduction
Background
Achondroplasia is a common, nonlethal form of chondrodysplasia. It is transmitted as an autosomal dominant trait with complete penetrance. De novo mutations cause 75-80% of cases. The mutation rate is estimated to be 0.000014 per gamete per generation. Cardinal features include short stature, rhizomelic shortening of the arms and legs, a disproportionately long trunk, trident hands, midfacial hypoplasia, prominent forehead (frontal bossing), thoracolumbar gibbus, true megalencephaly, and caudal narrowing of the interpedicular spaces.
Pathophysiology Read more…
