Scientists report in this month's Nature Genetics they have discovered
the gene that causes Van der Woude syndrome, the most common of the syndromic
forms of cleft lip and palate. The term "syndromic" means babies are born with
cleft lip and palate, in addition to other birth defects.
According to the scientists, the discovery could very possibly direct them to
genes involved in "non-syndromic" cleft lip and palate, one of the most common
birth defects in the world. Among Caucasians, non-syndromic cleft lip and
palate occurs in an estimated 1 in every 1,000 live births, and the frequency
seems to be even higher in some Asian countries, such as China and The
"Since there is so much clinical overlap between the two, we expect that
similar genes and maybe even the same genes will be involved in the
non-syndromic form," said Jeff Murray, M.D., a scientist at the University of
Iowa and an author on the paper.
Murray noted that the gene, called IRF6, seems to play a key role in the
normal formation of the lips, palate, skin, and genitalia. He said further
study of the gene should provide precise molecular clues into normal human
development and suggest specific biological strategies to prevent birth defects,
such as cleft lip and palate.
First described in the 1860s, Van der Woude syndrome (VWS) is involved in
about 2 percent of all cases of cleft lip and palate, occurring in approximately
1 of every 33,000 live births. Children with the syndrome are born with any of
four characteristic birth defects: Pits, or small indentations, in the lower
lip, cleft lip, cleft palate, and undeveloped tooth buds.
What has puzzled scientists is those with the syndrome inherit different
combinations of birth defects, not necessarily all of them. For instance, half
of the children born with VWS have cleft lip, 70 percent have pits in their
lower lip, 20 percent have cleft palate, and only about 10 percent do not have a
full set of teeth. More puzzling, siblings are often born with different
combinations of birth defects, though they inherit the same gene change.
Because the cleft lip and palate seen in people with VWS closely resembles
the non-syndromic condition, scientists long have been intrigued with
identifying its gene. The hope was the gene not only would permit genetic
testing of affected families, the gene might point them to the complex cascade
of molecular signals during early gestation that prompt the formation of the
lips and palate, critical information in developing viable strategies to prevent
In the mid 1980s, as scientists became more adept at identifying so-called
"disease" genes, laboratories launched their initial attempts to find the one
involved in VWS. Based on data from a case report of an individual with VWS
that was caused by a chromosomal abnormality on chromosome 1, Murray's group
confirmed that other individuals affected with VWS shared an irregularity in the
same region of chromosome one, the first step in finding the gene.
But, in trying to pinpoint the precise location of the irregularity, the
scientists eventually ran into technical difficulties. Part of the problem was
making sense of the region's unusual terrain, which in some people includes a
fairly large, but benign, deletion and long stretches of difficult-to-track
repeat sequences of DNA.
Another problem was simply wading through all of the genomic information that
had become available to them during the late 1990s. According to Brian Schutte,
Ph.D., a lead author on the paper and a scientist at the University of Iowa, one
of the first genes the group evaluated was IRF6, the subject of this month's
paper. However, based on a preliminary analysis, they initially excluded it as
the disease gene.
"We tested DNA samples from a subset of people with the syndrome, and we
didn't find any mutations in IRF6," said Schutte. "About this time, the full
DNA sequence map of the region became available to us. We suddenly had a long
list of other genes to evaluate and decided to move on from IRF6."
Added Murray, "At the time, we understood that we were excluding candidate
genes that could still potentially be the disease gene. But you always have to
choose the best place to focus your efforts, and our data at the time indicated
that it was better to move on to other candidate genes."
A break came last year while a visiting graduate student in Murray's
laboratory spoke on the telephone to a colleague in her native Brazil. "Her
colleague happened to mention that he had just seen so-called 'monozygotic
twins,' in which one had van der Woude and the other didn't," remembered
Murray. "She told of us about it, and we got quite excited actually."
Murray hypothesized that the twins were genetically identical with one
exception: The affected twin would have a change in the VWS gene. Shinji Kondo,
a post-doctoral fellow in Murray's lab, then sequenced the relevant portions of
DNA from the twins and, soon thereafter, they discovered a syndrome-causing
deletion in IRF6.
"I certainly knew it was possible in theory," said Murray. "But, to be
honest, if I knew as much then about twins as I do now, I might have been less
Murray explained that the theory hinged on the possibility the mutation
occurred soon after the twins divided into separate embryos, meaning all cells
in the body of the affected twin would carry the mutation. If it had occurred
later in the developmental process, after various distinct cell lineages have
emerged, only some of the affected twin's cells would have carried the
mutation. "If that were the case, we might have missed it," said Murray.
"Monozygotic twins are actually quite common in other complex conditions,
including diabetes and heart disease," added Murray. "I think our work offers
proof of principle that monozygotic twins are a powerful model to search for
genes involved in complex conditions, one that may have been overlooked in the
To confirm the discovery, Schutte and colleagues sequenced and found
mutations in IRF6 among 46 unrelated families with the syndrome. Interestingly,
the group also detected changes in 13 additional families with a related
condition called popliteal pterygium syndrome, or PPS. This rare disorder
involves the same birth defects as VWS, plus underdeveloped genitalia and webbed
skin on the back of the legs. Further confirmation was obtained by Mike Dixon's
lab at the University of Manchester in England. Dixon's lab showed that IRF6 is
made in all the tissues affected by both VWS and PPS during the critical times
Schutte said the gene's involvement in causing both conditions is not
necessarily surprising. Researchers have noted previously that some so-called
PPS families include members who only have orofacial abnormalities reminiscent
of VWS, not those in other parts of the body. "I think that as we learn more
about the biochemistry of IRF6, we'll be able to make better predictions about
how these syndromes will manifest themselves," said Schutte. "At the same time,
there are also probably many other genetic and environmental factors involved,
One intriguing possibility raised by this month's paper is cleft lip and
palate conceivably could be associated with some type of viral infection during
pregnancy. Though poorly studied, IRF6 is similar to other genes that help to
trigger the production of interferons, immune signaling proteins involved in
responding to viral infections.
Stressing that the viral connection is still extremely speculative, Murray
noted, "This would be a wonderful outcome of this paper because, in 2002 at
least, attacking viruses is much easier than manipulating genes. "
Already, the group has determined that IRF6 is highly expressed in the tooth
buds, hair follicles, genitalia, skin, and palate of the developing human
embryo. By further studying the gene and its protein, Schutte said it should be
possible to tap into the molecular signals that it helps to relay during human
development. "We know that IRF6 is a transcription factor, meaning it binds to
certain genes and allows their information to be copied, the first step in
producing a protein," he said. "We can now ask which genes it activates and
when? All of these genes might be involved in causing cleft lip and palate. Or
they could contribute to other birth defects. The point is we stand to learn a
great deal from this gene discovery."
The article, which is published in the October 2002 issue of Nature
Genetics, is titled, "Mutations in IRF6 cause Van der Woude and popliteal
pterygium syndromes." Its authors are: Shinji Kondo, Brian C. Schutte, Rebecca
J. Richardson, Bryan C. Bjork, Alexandra S. Knight, Yoriko Watanabe, Emma
Howard, Renata L. L. Ferreira de Lima, Sandra Daack-Hirsch, Achim Sander, Donna
M. McDonald-McGinn, Elaine H. Zackai, Ed Lammer, Art Aylsworth, Holly Ardinger,
Andrew C. Lidral, Barbara Pober, Lina Moreno, Mauricio Arcos-Burgos, Consuelo
Valencia, Claude Houdayer, Michel Bahuau, Danilo Moretti-Ferreira, Antonio
Richieri-Costa, Michael J. Dixon, Jeffrey C. Murray. The research was supported
by the NIDCR.