delayed myelination?

To make a long story short..I just found this page while researching my baby's problems. He had an MRI done at 11 weeks that showed delayed myelination. It was only that of a 3 week old amongst some other issues. He has hypotonia, but has made tons of progress in the past 6 weeks though. The therapist said if she didn't know his history now that she would say he's just a little low toned, but other than that normal. He also has these spells where he "checks out". He also has swallow dysfunction, reflux, a heart murmer caused by ASD and apnea. All of the genetic tests have come back negative so far. My nephew who is 16 months old had an MRI last week that showed his myelin developed to that of a 9 month old. Does anyone have any idea's as to what this might be or been through it?