Volume 16 Number 3, SPRING 1999

Special Intelligence

MORE THAN ANYTHING ELSE, IT'S SALLY B.'S LAUGH – A THROATY CHUCKLE AT ONCE EXPLOSIVE AND EMBRACING – THAT YOU REMEMBER ABOUT HER.

By Bruce Goldman

Sally B. is articulate. She is sociable. Her manner is expressive and polite, her vocabulary large and growing, her discourse pithy and punctuated by mirth. And if you gave her an IQ test she'd probably score somewhere between 60 and 80, placing her between the bottom 8 percent and the bottom 0.5 percent of the population (100 is the average score).

"People have always said that I'm retarded," she says. "I'm not. I just happen to be different. Last year I went to the Stanford genetics clinic, and they examined me and gave me a blood test. The blood test showed that there was a chromosome that was bent; and that's what makes Williams syndrome."

Sally B. was diagnosed last June, at age 48, with Williams syndrome, a rare condition she has had all her life. Williams syndrome occurs when a particular chunk of DNA is deleted from one parent's contribution to his or her offspring's total genetic heritage, or genome. Every cell in Sally's body is missing that DNA section, and thus is also missing one of the two copies of all the genes – something like 30 of them – normally residing there.

The effects of the missing DNA are striking. Perhaps foremost among them a pronouncedly uneven pattern of learning and thinking ability – strong in verbal skills, very weak in computation and in spatial reasoning.

The best way to learn about Sally B.'s medical condition is to let her tell you about it in her own words: "I like to read. I like music. I am fascinated with language. Generally I like people. I pretty much can make friends easily – I don't know a stranger!"

Indeed, a hallmark of Williams syndrome is extreme gregariousness, and Sally certainly appears comfortable in the presence of Uta Francke, MD, whom she's meeting for the first time today. Francke is a physician and professor in the Department of Genetics at Stanford University School of Medicine, and a Howard Hughes Medical Institute Investigator as well. She and her colleagues comprise one of a handful of labs worldwide that are conducting an intensive inquiry into the molecular genetics of Williams syndrome. Many of these researchers are convinced their work will identify some on the genes responsible for cognition, language and sociability – key aspects of what makes humans unique. The researchers also want to make a difference in the day-to-day lives of people like Sally B.

"Sally rejects the notion that she's retarded, and I think she's right," Francke says. "Our standard IQ tests are just not good for everybody."

Musicality is one area where Williams patients seem to have suffered no loss whatsoever. Says Sally: "I've always loved music. I have an organ and a keyboard. I play by ear." Another Williams patient, Gloria Lenhoff, has achieved some note as an opera singer. "Gloria is really amazing," Francke says. "I met her when I was in Southern California last week. She sang an aria from an Italian opera for me, and was absolutely incredible. She has perfect pitch. The tones and the speech are just unbelievable – and she cannot read music. She gave me an audiotape, on which she sings in 22 different languages and accompanies herself on the accordion."

Music is one thing, noise another. Many people with Williams syndrome are hypersensitive to loud sounds, says Francke. "A vacuum cleaner or mixing blender can just cause horror. One of those things we want to find out is why they're so hypersensitive to sound – what genes and what parts of the brain might cause that. It could be that the musicality and the hypersensitivity are somehow related."

Williams patients enjoy strong speech and language comprehension, although speech develops slowly in childhood. But they have tremendous difficulty with visual processing. Information presented on a classroom blackboard is lost on them. Drawing a picture is an exercise in futility. "My handwriting is…," Sally B. intones with a pause, "well, not good."

She acknowledges with a rueful chortle that she also finds math excruciating. Her father, Bob, who has accompanied her on this visit to Francke's office, agrees. "She has trouble with decimal points and with adding even simple numbers. She can come up with the answer, but not quickly," he says. She goes shopping by herself, her father adds, but when she does she rarely gives exact change to someone, because the subtractions are too bothersome.

Williams patients' bumpy intellectual profile and their engaging friendliness can obscure the plethora of physical symptoms that often beset them. Like many other Williams patients, Sally B. has premature arthritis. Long walks and even swimming are not her idea of a good time. "My balance isn't too good," she says. "I've had a couple of spills. Uneven ground doesn't like me – and I don't like it!" Her listeners laugh heartily, and so does she.

More than half of all individuals with Williams syndrome develop supravalvular aortic stenosis, or SVAS, a narrowing of the aorta because of thickening of the aortic wall. Corrective surgery is often necessary.

The Missing Snippet

IN THE EARLY 1990S researchers at the University of Utah studying familial SVAS, in which the cardiovascular defect (but none of the other typical Williams features) is passed along from one generation to the next, traced the defect to an inherited mutation in the gene coding for elastin, a protein that bestows elasticity upon tissues such as skin, joints, and blood vessels. The Utah researchers found that, among Williams patients, the absentee elastin gene was not merely deleted; it was but a part of a sizeable stretch of DNA, apparently containing several other genes, that was missing from one of the two copies of patients' chromosome 7. Such missing stretches are known as deletions.

Thus Williams patients are invariably missing one of the two copies of the gene for elastin, whose short supply probably accounts for yet another signature Williams syndrome characteristic: facial features that have sometimes been described as "elfin" or "pixieish." In combination with young patients' gregariousness, this can leave a lasting first impression.

"These children are really special," says Francke. "The first one I ever met was in the early 1970s, when I was an assistant professor of pediatrics at the University of California at San Diego. I'll never forget this patient. The door was open. The mother and the daughter came in. And the child let go of her mother's hand, walked straight to my desk, climbed on my lap and said, 'Hi, Doctor, how are you today?' This was a 6-year-old child. No child without Williams syndrome would do this. I was totally stunned. There's a total lack of stranger anxiety. They will walk up to anybody and be friends."

TV documentarians, seizing on young patients' incredible friendliness, expressive musicality, articulate speech and usually somewhat diminutive size, have succumbed to the temptation to depict them as "adorable." But that perception short-circuits as the children reach maturity.

"High school was terrible," Sally B. recalls. "People would poke fun at me every time they got a chance."

"Most of the adults with Williams syndrome whom I've met are very aware of how different they are from other people," says one of Francke's research associates, Risa Peoples, MD, a physician who has dealt clinically with a number of Williams cases. "I don't think that comes off in those television specials. The learning problems they have – especially with mathematics and with understanding things presented visually – make it extremely difficult for them to function in society, and a lot of them have difficult lives. They are quite aware of social cues and get a lot of very negative feedback from society, so as they get old they lose a lot of that stuff everybody finds so cute and adorable in the young children."

The Francke lab researchers' increasing contact with Williams patients has bred a growing empathy and a desire to explore not just the disease's exciting (to scientists) neurological features but its other clinical features as well, in the hope of improving the lives of these patients in the here and now.

Sally is lucky in that she has been spared SVAS. Nor did she suffer, to the best of anybody's recollection, from another trait common to Williams patients during infancy: faulty regulation of calcium levels in the blood, which triggers a colicky condition that can drive even the most loving parents to distraction before it fades away as the child gets older.

It was in Francke's lab a few years back that the search for the cause of that calcium-regulation disorder led to a critical discovery.

Look-alike DNA's Last Tango

AT ABOUT THE SAME TIME that the University of Utah lab was learning that a stretch of DNA containing the elastin gene was missing from one copy of Williams patients' chromosome 7, a pediatric endocrinologist from Spain, Luis Perez-Jurado, MD, PhD, was working in Francke's laboratory as a postdoctoral fellow in the Stanford Medical Genetics Training Program. Perez-Jurado wondered whether a particular gene known to be important in calcium regulation might possibly be one of those missing genes in the Williams deletion, like the elastin gene. If so, it might be contributing to the hypercalcemia of Williams syndrome.

To the growing fascination of Francke and other colleagues, Perez-Jurado eventually localized the calcium-regulatory gene to chromosome 7 – the chromosome in which the Williams deletion occurs. But the gene in question, it turned out, was located outside the deletion, so it couldn't have been playing a part in Williams syndrome.

However, Perez-Jurado had now learned enough about the DNA in and around the deleted section to make an important finding: At the edges of the DNA region whose deletion causes Williams syndrome are two DNA stretches that are nearly identical – a phenomenon known in molecular genetics as a "duplication." This duplication explains why, in virtually every Williams patient, a sizable and almost identical chunk of DNA is deleted from one copy of chromosome 7.

Just before a germ line cell divides to form eggs or sperm, the cell's chromosomes line up in two rows of 23, each maternal copy pairing up with its paternal counterpart; after the division, one full set of 23 chromosomes will wind up inside each new gamete thus produced. (Egg and sperm cells are unusual in that they carry only one set of 23 chromosomes instead of the usual two sets.)

The matching chromosome pairs do more than just line up. They snuggle together intimately, with their nearly but not quite identical DNA sequences in close alignment. And sometimes, in a kind of "last tango" aided by specialized enzymes, they exchange little bits of their look-alike DNA. Apparently, this "crossing over" stabilizes the chromosomes' positions while they await their final segregation into separate daughter cells.

But suppose that there were two look-alike DNA sequences some distance apart from one another on a chromosome. These duplicate sequences could cause major confusion by permitting a microscopic misalignment between the flirting paternal and maternal chromosomes. All that's necessary is for one of those look-alike sequences (say, the "upstream" sequence) on the paternal chromosome to pair up not with its correct counterpart occupying the same position on the maternal chromosome, but instead with that second, almost precisely identical sequence a little bit downstream on the maternal chromosome.

If you've ever taken a good look at a jammed zipper, you know what that would look like. A small misalignment among the zipper's teeth results in a few teeth on each side looping off uselessly instead of engaging with the other side. Substitute genes for teeth, and the chromosome-pairing analogy holds up pretty well. Each chromosomal copy ends up with a pinched-off loop of DNA between its copycat "upstream" and "downstream" sequences (the loop, as a result of the misalignment, would reside at a slightly different position on each chromosomal copy – a smidgen upstream on one side, a touch downstream on the other, just like what happens with a zipper). Should a DNA exchange then occur in that misaligned region, the enzymes responsible for the "slice and splice" operation may inadvertently chop that intervening loop (containing the "Williams genes") right out of a "donor" chromosomal copy, resulting in a corresponding deletion in the reconstituted "receiver" copy.

Tripping Over Genes

IF YOU COULD UNRAVEL one set of 23 chromosomes, splice them all together end to end into a single strand, and stretch that strand taut, it would be about a meter long. The Williams deletion is roughly one-half millimeter in length, or 0.05 percent of the total. That's enough to hold something on the order of 30 genes or so. Of that as yet unknown number, about 15 have been found, seven of them by the Francke lab, which has been looking at the genetics of this disease since around 1994.

Upon Perez-Jurado's elucidation of the DNA "breakpoints" of the Williams deletion, Francke grew very interested in exploring the molecular genetics of the disease thoroughly: What parts of that missing DNA strip code for the production of proteins? How many? Where do you find those proteins, within which cells in which tissues, and what kind of chemical company do they keep? What are their functions?

It would be easier to find genes if one already knew the exact chemical sequence of the whole deletion. But that's a big job: If each of the region's 1.5 to 2 million chemical units were the size of a typewritten letter, the entire document would be 3,000 or 4,000 pages long. As a first step, Peoples, already associated with the lab at that time, began the long, arduous process of creating a so-called map of the deleted region – establishing small "street signs" along the stretch of DNA so that a more systematic effort could be made at learning the exact sequence and identifying genes within it.

The team now includes three additional postdoctoral researchers: Yvonne Franke (no relation to Francke), Tamar Paperna and Yu-Ker Wang. All of Francke's colleagues are working on gene identification and characterization of seven genes they've discovered so far – sometimes inadvertently "tripping" over the genes in the course of creating the map of the region.

Not every one of those genes that are present in only one copy is necessarily a problem, Francke says. "For many diseases that are caused by enzyme deficiency, 50 percent of the gene product is enough. In this case we have to find genes for which 50 percent is not enough. These are interesting genes, and we've found a couple of those. They have roles in regulation of pathways or transcription factors, in particular those that work in the nervous system.

"But we've also found genes that are not expressed in the brain at all. They are expressed in the lung and in the gut, but not in the brain." These non-neurological genes are getting a heightened emphasis in the Francke lab because, while they may not unlock the secrets of cognition and sociability, they provide clues as to how to improve the lives of people with Williams syndrome – people like Sally B.

The real proof that any of these genes has anything to do with any particular aspect of Williams syndrome's features, says Francke, rests on identifying patients that have only lost function of that single gene and have the rest of the Williams syndrome region intact. Because Sally B.'s case is fairly representative, there's no point in rigorously checking out her genomic deletion in full detail; it's undoubtedly pretty much the same as the others that have been looked at so far.

Last Laugh

SALLY B.'S DIAGNOSIS last June was corroborated in the Stanford Cytogenetics Laboratory by a much quicker technique called fluorescent in situ hybridization, or FISH, in which a person's chromosomes are separated from one another, mixed with a fluorescently labeled chemical "probe" that binds only to the elastin gene and then vigorously washed. In Williams patients, one, but not the other, copy of their chromosome 7 "lights up" under microscopy.

Better late than never. Sally is glad to finally have an explanation for why she is different. And much to her delight, the revelation has led her to discover a community of people who share this difference.

Why did it take 48 years for a correct diagnosis? For starters, Sally B. has been spared SVAS, the symptom most likely to bring young Williams patients into their pediatrician's office. Second, Williams syndrome is a relatively recent medical discovery; it was first described in the early 1960s. And third, it's rare – perhaps one case in 20,000 people – so frontline clinicians aren't generally intimately familiar with it.

When Francke offers Sally B. a tour of the lab, she assents vigorously despite her understandable distaste for locomotion. She especially wants to look into a microscope and maybe get a glimpse of the notorious chromosome 7 with which her fate is entwined. Before the tour begins, Francke produces her copy of the Gloria Lenhoff tape and gives it to Sally, who is ecstatic. "Well, thank you! I'll enjoy it!" She hugs Francke. And she laughs.

An appropriate gesture. With a little luck, some patience, and continued scientific interest in their condition, Williams patients may, one day in the not-too-distant future, have the last laugh. SM