A friend has a two month old baby, born in Texas, USA.   At birth he
was a beautiful normal, healthy baby boy.  At one month of age he
began having seizures.  Now, at two months of age the seizures are
controlled with medication, but the baby is mostly comatose, having to
be fed through a tube.
He has been investigated by paediatric neurologists who can find
nothing wrong with him neurologically.
He has also been fully investigated by paediatric endocrinologists. 
They suspect a metabolic disorder.  He has been tested for all known
metabolic deficiencies in new born babies. They say he has a
deficiency of an unknown enzyme. Unless the enzyme is identified the
baby will not recover.
Can anyone help with any information for this distraught family?

First a word of clarification. It is obvious that the neurologists in
question found something neurologically wrong with this baby, if he is
indeed almost comatose and cannot feed. The issue is that they may not
be able to find anything wrong with the structure of his brain by
scanning (MRI, CT) or anything wrong on blood tests. I am sure that
they do not claim that he is normal or doing fine, they just cannot
give him a confident diagnosis.

Regarding the statement "Unless the enzyme is identified, the baby
will not recover": This may be strictly true, but this does not mean
that if the enzyme IS identified, he WILL recover. Unfortunately,
there are many enzyme deficiencies for which there are no known cures
or adequate treatment.

There is not enough information in your post for anyone to make a
diagnosis. However, if a member of my family were in this position, I
would make sure that the baby's evaluation was done in an academic
pediatric medical center (a pediatric hospital) and I would also
consider seeking a second opinion at a different pediatric medical
center for additional help.

I would also strongly assert that the fact that a diagnosis cannot be
identified or a specific treatment given does not mean that the baby's
physicians are unqualified - the scenario described above is sadly not
uncommon even in the best pediatric hospitals.