Achondroplasia

Achondroplasia (ACH) is the most common form of short-limb dwarfism occuring in 1 in 15,000 to 28,000 births and appears to be slightly more prevalent in females, but indiscriminent toward race (1-3). Evidence has been found in Egypt for cases of ACH dating back as far as 4500 B.C. (4). In simplest terms, ACH is a disease where the dwarfing of bones formed in the cartilage occurs (5). There are many features that accompany this disease including rhizomelic (proximal) shortening of the extremities, megalencephaly (enlarged brain), short stature, trident hand, and frontal bossing (prominent forehead) (1, 3, 4, 6-8). Expression of this gene at high levels is primarily found in cells of the nervous system and the cartilage rudiments and chondrocytes in the growth plates of developing bone (7, 9). Due to the fact that there are numerous types of skeletal dysplasia, some which appear similar to ACH at times, the only way for complete confirmation is to perform molecular techniques such as genetic testing (1, 4, 8).

The gene which is responsible for this disease, FGFR3, is located on chromosome 4 at 16.3, which is on the short arm near the telomere (4). Under normal circumstances, this gene forms fibroblast growth receptor 3 which interacts with a protein to begin a stream of signals that contribute to bone development and maintanence; it is also thought that this gene is also important in other tissue development (6, 7, 10-12). Some of the known pathways involved with FGFR3 are STAT1/3, STAT5, MEK1, ERK1, and MAP kinase signaling. Chondrogenesis and osteogenesis are two processes managed by these pathways and are greatly affected by a mutation (13-15). The sections of these pathways that involve and are affected by the mut...

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...s to interfere with bonding to the receptors. The final possibility uses CNP, which downregulates the activation in MAP kinase pathways in the chondrocytes (4).

ACH, is an interesting disease, one that after many years of research still remains a partial mystery. The fact that a single nucleotide on one chromosome can so greatly affect an individual is astounding, especially coupled with the fact that this mutation is so homogenious in genotype and phenotype. With more skeletal dysplasias being connected to FGFR3, research has increased to fully determine and define the pathways involved with this gene. Determining the reason for such a high mutation frequency and the link to paternal age are also being looked into. Once there is more understanding of how this mutation affects the body, treatments and possibly cures can be found for these individuals.