+------------MOD_PRED:N-ADJ-----------+                          
        +------------COMP_at:V-N------------+   +MOD:AD+MOD:AD+COMP_than:+COMP_of:V+     
        |               |                   |   |      |      |          |         |     
At its peak , the concentration of GENEXXX was some twofold higher than that of GENEXXX .
COMP_at:V-N (was,peak)
MOD_PRED:N-ADJ (concentration,higher)
MOD:ADJ-ADV (twofold,some)
MOD:ADJ-ADV (higher,twofold)
COMP_than:ADJ-N (higher,that)
COMP_of:V-N (that,GENEXXX)