Serf's parma: Yes, by anyone.
Mutantum mages use the mutantum magic virtue which combines the good effects of boosted, tethered and harnessed magic, but ties the character to House Mercere bloodlines.
The 'Mutantum only' bit is the Mastery skill(s) 'Boosted magic' IIRC, and one must either have the appropriate virtues to take this skill or be taught the spell by one with the skill - something like that.
Each of the Boosted magic, Harnessed Magic, and Tethered Magic Virtues are described as especially common among the Gifted mercere, but may be owned by any magus.