My 4 month old son has lissencephaly. what are the best possible ways to help his development starting now? physical and mental?

Seek help now: Get him started in physical and occupational therapy. He will need further help as he gets older. Good luck!

PT, OT and speech: Early intervention is the best thing you can do for any child who has developmental delays. A child with lissencephaly should be evaluated and receive therapy from a physical therapist, and occupational therapist & a speech therapist as soon as possible one the diagnosis is made. http://www.ninds.nih.gov/disorders/lissencephaly/lissencephaly.htm