Why is sickle-cell anemia considered pleiotropic?

How many alleles does the PAH gene for PKU have?
Why is the PAH gene also pleiotrophic?I want to know the different effects.
Answer:
Pleiotropic: 1. Producing many effects. 2. Multiple effects from a single gene. For example, the Marfan gene is pleiotropic with widespread effects and can cause long fingers and toes (arachnodactyly), dislocation of the lens of the eye, and dissecting aneurysm of the aorta.sickle cell anemia is not a monogenic disease; it is a multigenic disease. The latter is the product of pleiotropic genes (involved in secondary pathophysiologic events) and epistatic genes (same gene but with significant pathophysiologic consequences among individual=polymorphism).--%26gt; http://www.ncbi.nlm.nih.gov/entrez/query...# PKU occurs if a child has mutations in both copies (alleles) of a particular gene, the gene for the protein phenylalanine hydroxylase (PAH).
# A child can inherit two defective copies of the PAH gene if both parents are PKU carriers. (Each parent has one normal allele of the PAH gene and one defective allele.)
# Carriers do not have PKU because the normal copy of the PAH gene produces enough of the normal PAH protein. In genetic terms, the normal allele of the gene is dominant and PKU is recessive.
# If both parents are carriers, each of their children has: * One in four chance of inheriting the defective copy of the PAH gene from both parents. These children will have PKU.
* One in four chance of inheriting the normal copy of PAH from both parents. These children will not have PKU, and will not pass the defective PAH gene to any of their children.
* One in two chance of inheriting a normal copy of PAH from one parent, and a defective copy from the other. These children will be carriers like their parents.

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Pleiotropic is as defined above = a gene having multiple phenotypic expression.
I am surprised to hear that sickle-cell anemia is considered pleiotropic.
SC anemia is a MONOGENIC disease, the affected gene is the beta-globin gene (vital part of hemoglobin, the protein that transports oxygen in red blood cells).
SC anemia MIGHT be considered pleiotropic, since many similar gene products are involved in the generation of hemoglobin: SD disease, S/beta thalassemia patients do have sickle cell mutation, so you could say pleiotropic. In these cases there is another mutation as well, and both mutations are dominant (codominance).
PKU: There are at least 400 mutations of the PAH gene. The combination of any two will results in a very variable phenotype = pleiotropic.
Also, there are mutations of OTHER genes that may lead to the PKU-condition, hence the term: molecular heterogeneity.

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pleiotorphic means one mutation can affect several aspects of the phenotype and that is what happens in these diseases

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