Essay On Sonic Hedgehog

Sonic hedgehog (SHH) plays an important role in patterning various embryonic identities. (Johnson et al., 2014) Mutation in the sonic hedgehog enhancer leads to limb malformation in humans. There are 13 different point mutations and 10 duplications in humans involving the ZRS that have been shown to cause human malformation such as preaxial polydactyly, triphalangeal thumb and syndactyly. (VanderMeer and Ahituv, 2011) The role of the zone of polarizing activity control sequence (ZRS) is to produce and secrete SHH, which acts as a morphogen to control identity of each developing digit and specify the number of digits that form. (Gurnett et al., 2007) In this report I will discuss the type of mutation, identification of mutation, changes that
This misexpression is central to a group of limb defects, which are known as ‘ZRS associated syndrome’. (Lettice et al., 2011) In humans, there are three classes of mutation that have been proposed based on the limb phenotypes; single based changes throughout the region causes preaxial polydactyly (PPD), single base changes at one specific site ,for example, a G>A transition at position 404, which causes Werner mesomelic syndrome (WMS), and large duplications that cause polysyndactyly. ‘‘Cuban mutation’’ is the cause of PPD type II, which is the result of mutation 404G>A of ZRS. (Wieczorek et al.,
This condition is usually inherited as autosomal dominant characteristic. There are two type of polydactyly; the pre-axial (extra digit towards the hand or foot) and post-axial (extra digit is towards the lateral margin of the hand or foot). Polydactyl can occur at the same time when excess digits are fused together, which is called polysndactyly. Patients with polydactyl can exhibit Werner mesomelic syndrome. This condition is characterised by a short limb dwarfism as a result of hypoplastic tibia. WMS occurs due to specific point mutation at position 404. (Cho et al., 2013) patients with WMS, can also exhibit duplication of the ZRS region, which is the cause of type Haas polysyndactyly or triphalangeal thumb polysyndactyly syndrome. This condition doesn’t affect lower limb development. This suggests that different mutational mechanisms affecting the enhancer region of the shh gene demonstrate different phenotypic outcomes. (Wieczorek et al.,