Molecular Genetics and Studies Toward Gene 
Therapy for Metabolic Disorders 
Savio L. C. Woo, Ph.D. — Investigator 
Dr. Woo is also Professor in the Department of Cell Biology and Institute for Molecular Genetics at Baylor 
College of Medicine. He obtained his undergraduate degree in chemistry from Loyola College, Montreal, 
and his Ph.D. degree in biochemistry from the University of Washington, where he worked with Earl Davie. 
His postdoctoral research was done at the University of British Columbia, Vancouver, in the Division of 
Neurological Sciences. 
A major focus in my laboratory has been the 
analysis of human metabolic disorders at the 
molecular level. Phenylketonuria (PKU), the dis- 
ease under investigation, is an inborn error in 
amino acid metabolism that causes severe and 
permanent mental retardation in untreated chil- 
dren. The condition is caused by defects in the 
liver enzyme phenylalanine hydroxylase (PAH) 
and is transmitted from the parents to both boys 
and girls. In the United States it affects 300-400 
newborns a year, and 1 of every 50 individuals is 
an asymptomatic carrier of the disease trait. A sec- 
ond area under intense investigation is technol- 
ogy development for the cure of these genetic 
disorders by somatic gene therapy. The diseases 
being studied here include PKU and hemophilia 
B, which is transmitted from asymptomatic car- 
rier mothers to their sons. 
Prenatal Diagnosis for Phenylketonuria 
Our laboratory has isolated the human PAH 
gene by molecular cloning and used the cloned 
gene to analyze cellular DNA of normal and af- 
fected individuals. Extensive benign variations in 
this gene were discovered and used to trace the 
transmission of individual PAH genes from the 
parents to the children in PKU families. A fetus 
inheriting the same PAH genes as an affected sib- 
ling will have PKU. This has led to a prenatal 
diagnosis procedure for PKU in families with pre- 
viously affected children, and the procedure has 
been adopted in the United States and other west- 
ern European countries. 
Prognosis by Gene Analysis 
There is a wide range of severity of clinical 
symptoms among PKU patients, and their treat- 
ment depends on measurement of the phenylala- 
nine level in blood, which is often highly vari- 
able. The development of an independent 
method for the determination of prognosis is im- 
portant for proper management. We have ana- 
lyzed the mutations in the PAH gene of a large 
number of PKU patients who have been closely 
supervised for the past 20 years. The severity of 
their clinical conditions is primarily dependent 
on the inheritance of mutations in their PAH 
genes that are either totally or partially defective. 
In the future this correlation will allow physi- 
cians to prescribe proper medical treatment after 
simple gene analysis. 
Population Dynamics 
A number of these PKU genes have distinctive 
distributions in the European continent. One is 
very prevalent in eastern Europe, and its fre- 
quency decreases in a gradual fashion from east to 
west. These results suggested that the mutation 
occurred in eastern Europe some time ago and 
was then spread throughout the European conti- 
nent by migration of people in prehistoric times. 
Two other prevalent PKU genes are very frequent 
in either northern or southern Europe but less 
frequent in the neighboring countries. When sim- 
ilar analysis was performed in Israel and China, 
independent centers of major PKU mutations 
were also discovered. These results strongly sug- 
gest that multiple PKU mutations occurred inde- 
pendently in various regions of the world and 
then spread into neighboring areas in Europe and 
Asia. 
Somatic Gene Therapy 
The other major goal of our laboratory is to ex- 
plore the potential for somatic gene therapy of 
genetic disorders. The PAH gene has been in- 
serted into the genome of an incapacitated virus. 
The recombinant viruses are able to transduce 
mammalian cells and incorporate themselves 
into the genome of the host cells, but they are no 
longer able to produce new virus to continue the 
infection process. The recombinant viruses were 
used to transduce cultured rodent hepatoma cells 
and normal liver cells, thereby conferring upon 
them the ability to synthesize the corresponding 
human enzyme. 
These results have led to the development of 
hepatocyte transplantation technologies in labo- 
ratory animals. A variety of inert substances were 
used as support for mouse liver cells prior to 
transplantation, but the transplanted hepatocytes 
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