Genetic Control of Hemoglobin Synthesis 
Yuet Wat Kan, M.D., D.Sc. — Investigator 
Dr. Kan is also Louis K. Diamond Professor of Hematology in the Departments of Laboratory Medicine and 
Medicine at the University of California, San Francisco. He received his M.D. and D.Sc. degrees from the 
University of Hong Kong Medical School. After internship and residency at Queen Mary Hospital, Hong 
Kong, he obtained postdoctoral training in hematology at Peter Bent Brigham Hospital, the Massachusetts 
Institute of Technology, Royal Victoria Hospital at McGill University, and the Children 's Hospital, Boston. 
Dr. Kan has received numerous honors, including the Gairdner Foundation International Award and the 
Albert Lasker Clinical Medical Research Award. He is a fellow of the Royal Society (London ) and a member 
of the National Academy of Sciences and of the Academia Sinica (Taiwan ). 
THE focus of our research is the molecular 
basis of genetic diseases affecting the hemato- 
poietic or blood-forming cells. The two diseases 
we have studied in depth are sickle cell anemia 
and thalassemia. Both result from abnormal glo- 
bin production and constitute important health 
problems in the Mediterranean region, Africa, the 
Middle East, and Asia. In the United States these 
disorders occur frequently among people of Afri- 
can, Italian, Greek, and Asian descent. We have 
defined the mutations that give rise to these de- 
fects and devised DNA analyses for their detec- 
tion. In addition, we are studying the control of 
globin gene expression in red cell precursors and 
the signals that switch these genes from fetal to 
adult globin production. 
Previously we demonstrated that the common 
genetic defect in a-thalassemia is deletion of the 
a-globin structural gene. We also defined some of 
the molecular lesions in jS-thalassemia. These 
studies led to our ability to detect thalassemia by 
analysis of fetal DNA. 
We initiated a new method of linkage analysis 
using restriction endonucleases to detect poly- 
morphism in DNA sequences and applied it to 
tracing the evolution of the sickle and thalasse- 
mia mutations. Restriction enzyme site polymor- 
phism is now an important tool for detecting 
many genetic disorders and for mapping the ge- 
netic loci of many diseases. 
We developed a method for prenatal diagnosis 
of sickle cell anemia and thalassemia. Initially, 
fetal samples were required. With the advent of 
recombinant DNA technology, mutations in the 
human genome can be analyzed directly using 
DNA obtained by amniocentesis or chorionic vil- 
lus biopsy, permitting early in utero diagnosis of 
these conditions. 
Prenatal Diagnosis of Sickle Cell Anemia 
and Thalassemia 
The polymerase chain reaction has made it pos- 
sible to diagnose many point mutations rap- 
idly. For sickle cell anemia, practical nonradio- 
active tests are now available. In the case of 
(S-thalassemia, however, the need to diagnose 
multiple mutations makes these tests somewhat 
tedious, especially in the developing countries 
where the disease is common. Hence we are now 
devising a rapid approach using the reversed dot 
blot principle. Oligonucleotides corresponding 
to the mutations common in a given area are im- 
mobilized on a filter; the test DNA is amplified 
and hybridized to the oligonucleotides; and one 
of several nonradioactive methods is then used 
for detection. We believe this procedure will fa- 
cilitate prenatal diagnosis of i8-thalassemia on a 
broad scale. 
Control of Globin Gene Expression 
We are studying the factors that control the tis- 
sue- and development-specific expression of the 
human globin genes. Synthesis of the globin 
chains is precisely coordinated during develop- 
ment. The embryonic e- and f-globins, which are 
synthesized in the early embryo, are replaced in 
the fetus by the a- and 7-globin chains. Prior to 
birth, the /3-globin chain is known to become pre- 
dominant over the 7-globin chain; but the factors 
that control the expression of the /3-globin gene 
in the bone marrow cells and coordinate the ex- 
pression of the globin genes during development 
have not yet been elucidated. We are now study- 
ing the DNA sequences and protein factors that 
govern the expression of these genes. 
Recently DNA elements that are important for 
the control of the tissue-specific and develop- 
ment-specific expression of the globin genes 
have been revealed. This sequence is known as 
the locus control region, or LCR. In the jS-globin 
gene, the LCR contains four hypersensitive sites, 
which contain consensus sequences that bind 
trans-acting factors. We have been studying the 
cis sequences, which are important for protein- 
DNA interactions in two ways. 
First, we have determined by mutation analysis 
of these sequences, using both DNA-transfection 
and transgenic experiments, that important core 
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