about chromosomal mutations and their disorders

There are four types of chromosome mutations; deletion, insertions, inversions, and translocations. Deletions are when a chromosome segment is lost. Chromosome translocations are when a segment from one chromosome is transferred to another. Duplication is when a chromosome transfers to it's homogulous chromosome, which gives it a duplication of some genes. Inversion is when a segment of a chromosome arm is inverted. In chromosomal mutations, I'm particularly interested in the disorders that come with chromosomal abnormalities.

Humans have 23 pairs of chromosomes, with one pair of sex chromosomes, and 22 pairs of automosomes. Many genetic disorders result from when these chromosomes are imbalanced. These imbalances occur in roughly 0.6% of live birth, which often results in dysmorphism, malformations, or developmental disabilities. Such gene imbalances cause consequences, and cause 25% of all miscarriages and stillbirths. It also causes 50%-60% of first trimester miscarriages.

numeric abnormalities (aneuploidies) result from the loss or gain of a whole chromosome. Most of aneuploidies are a product of irregular seperation of chromosome pairs during meiosis. Aneuploidies are one of the most common cytogenic abnormalities. The most common mosonomy is the X chromosome (45,X) found in Turner's syndrome. Trisonomy (three duplicates of a specific chromosome) causes Down syndrome/trisonomy 21, which occurs in roughly 1/800 of live births.

A counter to aneuploidies are structural chromosomal abnormalities which result from breakage and the fixing of chromosome arms over time. Structurwl chromosomal abnormalities sometimes result in a gain or loss of material. There are two types of the deletions that may occur in structural chromosomal abnormalities; terminal deletion and interstatial deletion. A terminal deletion results after a single break in the chromosome, with the loss of the segment lateralto the break. An iinterstatial deletion results after two breaks in the chromosome, with the loss of said interveneing segment, and the joining of the remaining segments. Duplications are also caused in structural chromosomal abnormalities. They are caused by the gaaining of a copy of a chromosomal segment at the original location on the chromosome. They may be in inverted or direct orientation.

Other abnormalities do not result in a gain or loss of genetic material. This includes inversions (caused by a two break event with each end reversing the intervening chromosomal segment),translocations (the exchange of chromosomal segments between 2 or more chromosomes), and insertions (when a segment of one chromosome is translocated and inserted into a new region of the same chromosome, other homolog, or nonhomologous chromosome).

I'm getting a bit tired of explaining all the technical stuff, so now I want to move on onto the other topic that i'm really interested in.

A gene is a segment of DNA that contains the code for a specific protein which functions in one or more types of cells in the body. They contain instructions that determine how the body should look and function. So when a part of the chromosomes are missing, a number of syndromes may occur. They are called chromosomal deletion syndromes. They tend to cause birth defects and limited intellectual and physical development. In a some cases, severe birth defects from this can cause affected children to die at infancy or early childhood.

One of these syndromes is called Cri-du-Chat (cat's cry) syndrome. This is a rare syndrome which occurs when chromosome 5 is missing. The size of the deletion varies, and people who have larger deletions are usually more severly affected. The name comes from how affected newborns may come out with a high pitched cry which sounds like a cat, however some cases may not do this. Physical features of this syndrome are low birth weight, a small head, with a round face, small jaw, wide nose, widely seperated eyes, crossed eyes, and irregularly shaped ears set low on the head. Webbed toes and fingers are common as well. In growing children, there is limited mental and physical development. Heart defects are present sometimes as well. Thhose affected often continue living with this syndrome, but with substantial disability. The way that you can help those with this syndrome is to be supportive.

Another syndrome is called Wolf-Hirschhorn syndrome. This occurs when part of chromosome 4 is missing. Children with Wolf-Hirschhorn syndrome may have epilepsy, scalp defects, cleft palate, delayed bone development, colobomas of the iris, drooping upper eyelids, and a broad/beaked nose. Males may have cryptorchidism (undescended testes). Some have immune deficiency, which is when their body is less able to fight infections. Many of the children with this syndrome die during infancy.

There are also syndromes caused by duplication. One of the syndromes are called Down Syndrome. The risk of this syndrome increases with the age of the mother. However, most births occur to younger women, which mean 20% of all births with Down Syndrome occur to women over 35. Women with Down Syndrome are 50% likely to pass it on to their child, and is barely ever passed on by males, because males with Down Syndrome are typically infertile, unless they have mosaic Down Syndrome. This means those with Down Sydromes also have a mixture of two types of cells. Children with Down Syndrome often have delays in developing motor and language skills, however it varies. There is an increased risk in depression in childrena nd adults.

Visual ohysical developments with this disorder include a small head and face that is broad and flat, slanting eyes, and a short nose. however some newborns can still appear without these characteristics at birth, but then later develop these facial features during infancy. The tongue is often large, and ears are often small, rounded and set low in the head. There may be extra skin around the back of the neck. Those effected frequently have low facial tone, which combined with the larger tongue, causes children to hold their mouth open. Many newborns have heart and gastrointestinal defects. The most common of these heart defects are ventricular septal defect and atriventricular septal defect. 5% have gastrointestinal problems. Hisrschsprung disease and celiac disease are also more common. They may ahve hearing loss and are prone to frequent ear infections. They may also have vision problems and have cataracts. The joints in the neck may be unstable, which causes compression of the spinal cord, which also leads to changes in gait, usage of the arms and hands, bladder/bowel infection, or weakness. Many with Down Sydrome develop thyroid disease and diabetes. Ways that you can help those with Down Syndrome is genetic counseling and support.