** Shares of Australia's Neurotech International NTI.AX rise as much as 52.6% to A$0.029, their biggest intraday pct gain since early-July 2020
** Stock at its highest level since April 23
** NTI stock up 10.5% currently
** Biopharmaceutical co says U.S. FDA granted rare pediatric disease designation for drug candidate, NTI164, for treatment of Rett syndrome
** Rett syndrome is a rare genetic neurological and developmental disorder that affects ways in which brain develops
** Nearly 15.3 million shares change hands, 13.2x the 30-day average volume
** Stock has fallen 61.8% this year, as 0024 GMT
(Reporting by Roshan Thomas in Bengaluru)
((Roshan.Thomas@thomsonreuters.com))