Can you please describe the autism disorder where kids bite their lips off?

No specific name: There is not a variant of autism in which children bite off their lips. Some children with autism engage in self injurious behavior which could include hitting, pinching, and lip biting/chewing. They may also engage in these behaviors as part of an ocd routine or even as a sensory seeking mechanism. Behavioral or therapeutic interventions may be helpful to decrease the behavior. Meds may be needed.

Lesch Nyhan Syndrome: With self-mutilation is not associated with behaviors categorized as autistic spectrum disorder. However, ASD can present as a separate neurodevelopmental disorder in any child with a specific genetic or epigenetic set-up for it, whether they have another inheritable disorder or not. See http://www.Nlm.Nih.Gov/medlineplus/ency/article/001655.Htm.