Bittrex made the following announcement about de-listing of some alt-coins:

Thank you for using bittrex.com.

We will be removing the following wallets on 05/01/2016. Once removed, we will not be able to retrieve your funds. Please remove all coins ASAP. Note, that some of these coins have broken blockchains where we will not be able to send coins.

No exceptions will be made once the wallets are removed.

     Notice: The following wallets will be removed. Please withdrawal any coins you may have in these wallets.
Symbol   Coin Name
ASN   Ascension
AXIOM   Axiom
CF   Californium
CRAVE   Crave
DIBS   Dibbits
GEN   Genstake
GSM   GSMCoin
HYP   HyperStake
KOBO   KoboCoin
LDOGE   LiteDogecoin
M1   SupplyShock
NKT   Nakas
OCTO   OCTO
OPAL   OpalCoin
SHELL   ShellCoin
XRA   RateCoin
XSI   StabilitySharesXSI

     Notice: The following wallets will be removed due to broken block chains.  These coins cannot be withdrawn.
Symbol   Coin Name
BST   BitStone
BTCRY   BitCrystal
CHILD   X-Children
CIRC   CryptoCircuits
DRKT   DarkTron
DUB   Dubstep
GLOBE   Global
GRAV   Graviton
GRM   GridmasterCoin
IBITS   iBits
KTK   KryptKoin
MACRO   MACRO
MYST   MystCoin
OMC   Omnicoin
SHIBE   ShibeCoin
VMC   VirtualMiningCoin
XBS   BitStake
XWT   WorldTradeFunds