 The increased decline tends to occur in the higher frequency range, with a rate of around 0.8-2.2 dB a year.Turner syndrome is caused by the absence of one complete or partial copy of the X chromosome in some or all the cells.The abnormal cells may have only one X (monosomy) (45,X) or they may be affected by one of several types of partial monosomy like a deletion of the short p arm of one X chromosome (46,X,del(Xp)) or the presence of an isochromosome with two q arms (46,X,i(Xq)) Turner syndrome has distinct features due to the lack of pseudoautosomal regions, which are typically spared from X-inactivation.