CHILD'S BODY REPAIRS RARE GENETIC DEFECT : SCIENTISTS MARVEL, DOCUMENT CORRECTION OF CRUCIAL ERROR IN ONE STRETCH OF DNA.

Byline: Malcolm Ritter Associated Press 

The faulty genes that Jordan Houghton inherited could have killed him in early childhood. They killed his brother, Beau, at 18 months.

But marveling scientists report that Jordan has managed to heal himself, returning a flawed gene to normal.

Today, the Stanton, Mich., youth is a healthy 13-year-old who builds tree houses, earns A's and B's and plays saxophone in the school band.

Somehow, at some unknown time, Jordan's body rewrote his genetic legacy and stopped his disease, correcting a tiny but crucial typographical error in one stretch of DNA. The fix may have occurred first in just one cell of his body. That would be akin to taking a desk piled high with multiple stacks of paper, all photocopies of a single, thousand-word treatise, and fixing the word ``knit'' to ``knot'' on just one page.

``This little boy, instead of dying, got better,'' said Dr. Rochelle Hirschhorn of the New York University Medical School. She led a team of researchers who describe their investigation of Jordan's remarkable case in the July issue of the journal Nature Genetics.

This is the best-documented example of a very rare event, Dr. Hagop Youssoufian of Brigham and Women's Hospital and Harvard Medical School, told the Associated Press. A gene expert familiar with the report, he said he believes fewer than a dozen examples of such natural gene fixes have been reported.

Jordan was born with ADA deficiency, a rare condition that occurs about once in 1 million births. In this disease, cells have defective versions of a gene that normally directs them to make ADA enzyme, a ``housekeeping'' protein that eliminates substances that can poison immune system cells.

With a defective gene, a cell makes little or no ADA enzyme. That devastates the immune system and leaves the patient vulnerable to recurring infections.

Most children with ADA deficiency can be treated with bone marrow transplants or regular injections of the missing enzyme. Some have gone through an experimental therapy that tries to equip blood cells with normal versions of the ADA enzyme gene. It is unclear whether that helps because those children are also getting enzyme injections.

As an infant, Jordan was plagued with recurring pneumonia, diarrhea, boils and sinus infections. He grew slowly. When he first visited Dr. Lawrence Kurlandsky of Grand Rapids, Mich., for pneumonia at 2, lab tests showed major trouble in the immune system.

``You think, oh, my gosh, he ought to be overwhelmed with infections,'' Kurlandsky said about lab results. But Jordan's infections responded to common medication, and the child kept recovering.

Jordan's brother Beau, on the other hand, shared many of the same ailments but did not respond to medications. Beau succumbed to pneumonia when Jordan was 4.

Jordan never needed a marrow transplant or enzyme injections, Kurlandsky said. At 5, ``he all of a sudden started doing quite well with very little help from me,'' the physician said. Jordan's health has been basically normal since he was 8.

``We haven't had any serious problems for the last four, five years,'' said Jordan's mother, Sue Ellen Houghton. ``He hasn't even had a cold the last few years.''

In their report, Hirschhorn, Kurlandsky and co-workers present evidence that a defective gene was repaired naturally. How the boy's body accomplished that remains a mystery. It's not surprising that genes mutate, but the process most commonly creates defects, like those that encourage cancer, rather than removes them, as in Jordan's case.

Everybody inherits two copies of the ADA enzyme gene, one from each parent. The disease occurs only when both copies are defective.

The Nature Genetics report shows that Sue Ellen and David Houghton both have one defective copy of that gene, although their flaws are different, and they passed them along to Jordan.

In some of the boy's blood cells, one gene copy has the mother's defect and the other has the father's flaw, showing clear inheritance of the potentially lethal double dose of defects.

But others of Jordan's blood cells are different. They still show the father's flawed copy. But the gene copy from his mother has become normal. The tiny but devastating defect is gone. The gene is repaired. Out of more than a thousand crucial chemical links in the ADA enzyme copy, the single incorrect link has been replaced by precisely the right one.

The initial fix may have happened in a single blood cell. But that cell, with one normal copy of the gene, would alone have been able to make more ADA enzyme than multiple cells with only defective copies. That would give the cell a growth advantage, allowing it to flourish and produce offspring that inherited the same advantage, allowing them to flourish, too.

The result: a burgeoning population of genetically repaired cells that could make enough ADA enzyme to clear out potential toxins, thus strengthening the immune system and easing Jordan's illness.

Nobody knows when or how the fix happened - not even whether it started before or after birth.

Nor is it clear whether the repaired cells will be able to suppress the disease for the rest of Jordan's life, Hirschhorn said.

But ``so far he's doing shockingly well,'' Kurlandsky said. ``In fact, he probably doesn't even need me.''

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Photo

PHOTO Jordan Houghton, 13, practices on his saxophone. Thehealthy boy inherited a gene flaw that fixed itself.

Associated Press