What problems can an underdelevoped liver cause in a 7 week old baby boy?

my boy was born on 2-20 and was losing weight he was 8.13 at birth and he droped to 7 lbs on the this sat we are at the hospitle now and they keep saing it is somthing do do with his liver but thay dont know what is is they guess it is underdeveloped liver or his liver is not makeing the enximes he need to digest his food but that wont explain it into tuems i can understand someone please explain it to me