Sex-Chromosome Abnormalities and Genetic Disorders

Not only do problems occur when a gene for a disorder is inherited and expressed, but there can also be chromosomal abnormalities.

Sex-chromosome abnormalities

Klinefelter syndrome - XXY.  Tall (average height is over 6 feet), undeveloped testes, sterile, breast development, and incomplete masculinization of the body build.  They also often have social and learning problems.  Many of the problems are effectively treated with T, although this is ineffective in treating the sterility.  The sterility is due to the failure to produce sperm.  Sexual function is normal.  1/600 live male births, according to your text. There are other variants of Klinefelter - they may have even more copies of the X chromosome.  There are other variants of Klinefelter - they may have even more copies of the X chromosome.  

Turner syndrome - XO.  Short with a webbed neck.  May be mentally retarded and sexually underdeveloped.  Due to the lack of a second X chromosome, the ovaries do not develop normally and may not function fully.  Puberty will not normally - female hormones must be supplied.  Estimated to occur in 1/3,000 live female births.

XYY - once believed that this combination lead to increased aggression.  No evidence for this, however.

Some genetic birth defects and their characteristics:

Cystic Fibrosis - recessive disease that leads to a decreased resistance to respiratory diseases.  What are affected are the glands involved in the production of mucus, saliva, and sweat.  A number of organs are also affected.  Not only is there a decrease in disease resistance, but dehydration is also frequent.  Medicine can be used to increase the life expectancy of those with cystic fibrosis, but the only way to develop a cure is through gene therapy.  This is an autosomal recessive disorder.

Tay-Sachs Disease - some disorders are more likely to be found in certain groups of people, they occur more frequently in people of a particular ancestry.  Tay-Sachs is seen most frequently in ancestors of Eastern European Jews. This is an autosomal recessive disorder.

Phenylketonuria - (PKU) - North Europeans.  The nice thing about PKU is that it is a disorder that, once identified, can be dealt with effectively.  The individual will still have PKU, but problems due to this disease can be prevented.  Does anyone know what is wrong when someone has PKU?  PKU is a lack of an enzyme needed to digest phenylalanine.  The inability to digest this amino acid leans to an accumulation of it that then produces brain damage.  If untreated mental retardation and hyperactivity may result.  If, however, levels of phenylalanine are kept at a minimum, there is no problem.  Here is a case where a change in the environment can prevent the development of a problem.  PKU is seen in about one of every 10,000-20,000 births.  PKU occurs primarily in whites. Autosomal recessive.

Sickle cell anemia - African Americans, Latinos.  Sickle-cell alters the shape of red blood cells (RBCs), leading them to die quickly.  The loss of RBCs produces anemia and then the failure of the cells to carry oxygen leads to an early death.  About 1/400 African Americans is affected and about 1/10 are carriers.  About 1/20 Latinos are carriers. Autosomal recessive.

Huntington's Disease - a dominant genetic disease, if you have the gene you will eventually have Huntington's Disease.  We now know its location, it's found on chromosome 4.  It affects the CNS, but not until around the age of 35.  When it starts, there is progressive mental deterioration and problems with involuntary muscle movements.

Down syndrome - this is one disease that I think gets a lot of attention - that people are quite aware of.  It is due to aA picture of a baby boy who has Down's Syndrome. chromosomal abnormality.  Instead of a pair of the 21st chromosome, 2 chromosomes, there are 3.  Down syndrome can also be called trisomy 21.  It is one of the more frequent problems seen - occurring in 1/1,000 births, according to a 1990 paper.  

Thus, there are a number of diseases that are inherited on genes, as well as problems that can be traced to chromosomes. 

In addition to inherited diseases, susceptibility to some diseases can also be passed on in the genes - at least that's what all the evidence suggests.  


Bipolar Disorder (AKA "Manic Depression")


Alzheimer's Disease

These are the ones mentioned in your text - the problems that most clearly have a genetic component.  There are, however, many others.

In addition to chromosomal irregularities such as trisomy 21 (Down syndrome), there are also disorders produced due to abnormalities in the sex chromosomes:

Prenatal Testing