Achondroplasia

1. Describe the phenotype of individuals with achondroplasia, a common form of dwarfism.

Individuals with achondroplasia exhibit short stature, short limbs, a long torso relative to the limbs, a large head with a broad forehead, underdevelopment of the midface (depressed nose bridge), and hyperextensibility of the joints with the exception the elbow where movement is limited.

(http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=100800)

2. Achondroplasia is the result of a mutated gene.

a. What is the chromosomal location of this gene?

The chromosomal location of the gene is 4p16.3.

(http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=100800)

b. What protein does this gene code for? What is the normal function of that protein?

This gene codes for the fibroblast growth factor receptor-3 protein. The normal function of this protein is to regulate bone growth by slowing the production of chondrocytes.

(http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=gnd.section.256)

c. What is the most common mutation?

The most common mutation of the FGFR3 gene is a glycine to arginine change located in, at nucleotide 1138 of cDNA. (http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=134934&a=134934_AllelicVariant0001)

d. What change in the protein results from this mutation?

The change in the protein occurs in codon 380. The amino sequence changes from GGG to AGG and in rare cases to CGG.

(http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=100800)

3. Most cases of achondroplasia arise due to new mutations and are not inherited. Explain.

Achondroplasia is caused by a mutation in the FGFR3 gene. According to the NCBI, “nucleotide 1138 of the FGFR3 gene may be one of the most mutable bases in the human genome.”

(http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=134934&a=134934_AllelicVariant0001)