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ACHONDROPLASIA(OMIM#100800)-HYPOCHONDROPLASIA(OMIM#146000)

 

        Achondroplasia, is a kind of short- limb  dwarfism. Affected individuals exhibit short stature

caused by rhisomelic shortening of the limbs,characteristic facies with frontal bossing, exaggerated

lumbar lordosis,limitation of elbow extension and trident hand.

  Large head and hypoplasia of the midface may also present. The phenotype of this

osteochondrodysplasia is well distinctive and easily identified clinically and radiologically

at birth. The gene FGFR3 is mapped to 4p16.3 and plays an important role to osteogenesis and

development of bones. About 99%+ of the cases are due to two pathogenic mutations,c.1138g>a

and c.1138g>c. Most of these pathogenic mutations present de novo (about 80% of all cases).

There is also the paternal age effect. Achondroplasia is inherited in a dominant autosomic pattern.

     The frequency of this sceletical dysplasia is about 1/15000 of births.

 

    Hypochondroplasia is similar to achondroplasia but the sceletical abnormalities are much milder

than those of achondroplasia.The FGFR3 gene plays as achondroplasia, the main role to the genesis

of this dysplasia.There is a distinc hot spot mutation,c.1620c>a

 However, in contrast to achondroplasia, the clinical and radiological findings in HCH, have much

more value because of the genetic heterogeneity of it. In a great percentage of the affected

individuals the pathogenic mutation carries de novo.

      HCH, is inherited in a dominant autosomic pattern. The frequency is  about 1/15000-1/45000

of births

 

     Important note: The FGFR3 gene is involved also in the diagnosis of MUENKE syndrome,negriciance achanthosis and thanatropic dysplasia.