Apex domains cannot have CNAME records.
Question and response
Question
dig tuthost.com. NS
Answer
tuthost.com. 5 NS ns1.tuthost.com.
tuthost.com. 5 NS ns4.tuthost.com.
tuthost.com. 5 NS ns3.tuthost.com.
tuthost.com. 5 NS ns2.tuthost.com.
Authority
The response has no authority records.
Additional
ns1.tuthost.com. 5 A 91.203.4.6
ns2.tuthost.com. 5 A 91.197.185.59
ns3.tuthost.com. 5 A 51.255.206.38
ns4.tuthost.com. 5 A 192.99.59.119
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0