Abnormal  amounts  of  trinucleotide  repeat sequences can cause human
   genetic  disorders  such  as  fragile  X syndrome, Huntington disease,
   myotonic  dystrophy,  and  spinobulbar muscular atrophy. The number of
   repeats   may  increase  in  each  generation,  resulting  in  genetic
   anticipation: earlier age of onset and more severe of symptoms.