s ▁gene ▁defect ▁mainly ▁affect s ▁neural ▁cells , ▁a ▁patient ▁with ▁the ▁H EX A ▁mut ation ▁will ▁experience ▁a ▁quick ▁d eter ior ation ▁of ▁motor ▁and ▁mental ▁function ▁before ▁dying ▁around ▁the ▁age ▁of ▁three ▁or ▁four . ▁[ 8 ] ▁ ▁A ▁“ k no ck out ” ▁model , ▁which ▁is ▁a ▁mouse ▁that ▁has ▁been ▁gen et ically ▁modified ▁to ▁observe ▁the ▁effects ▁of ▁in activ ation ▁of ▁or ▁damage ▁to ▁certain ▁gen es , ▁found ▁that ▁the ▁m ice ▁that ▁were ▁admin ister ed ▁the ▁H EX A ▁gene ▁experienced ▁many ▁of ▁the ▁same ▁sympt oms ▁of ▁T ay - S ach s , ▁with ▁one ▁exception : ▁G M 2 ▁bu il dup ▁was ▁distributed ▁differently ▁in ▁the ▁bra ins ▁of ▁the ▁m ice ▁than ▁in ▁those ▁of ▁a ▁typical ▁human ▁T ay - S ach s ▁patient . ▁[ 9 ] ▁This ▁model ▁has ▁allowed ▁scient ists ▁to ▁research ▁gene ▁ther ap ies ▁for ▁H EX A ▁defect s . ▁One ▁study , ▁done ▁on ▁m ice , ▁successfully ▁re est ab lished ▁beta - hex o amin id ase ▁levels ▁and ▁removed ▁the ▁to xic ▁cell ▁bu il dup ▁by ▁using ▁a ▁non - rep licated ▁Her pes ▁simple x ▁vector ▁to ▁code ▁for ▁the ▁missing ▁gene . ▁[ 1 0 ] ▁ ▁References ▁ ▁Further ▁reading ▁ ▁External ▁links ▁▁▁▁▁▁▁ ▁National ▁T ay - S ach ’ s ▁D ise ase ▁Site ▁ ▁Category : Gen es ▁on ▁human ▁chrom os ome