Sci­en­tists study if Pap smear could spot birth de­fects early

Kuwait Times - - HEALTH & SCIENCE -

A sim­ple Pap smear may one day of­fer a way to screen for birth de­fects a lit­tle ear­lier in preg­nancy than to­day’s pre­na­tal tests.

Women typ­i­cally get a Pap dur­ing early preg­nancy, and Wayne State Univer­sity re­searchers re­port Wed­nes­day that they can cap­ture enough fe­tal DNA from the cells that test ex­tracts to check for ge­netic ab­nor­mal­i­ties.

The new study is very small, and much more re­search is needed. But if the ap­proach even­tu­ally pans out, re­searchers say it might be pos­si­ble to use as early as five weeks into preg­nancy and to de­tect more dis­or­ders non­in­va­sively.

Aside from bet­ter known chro­mo­some ab­nor­mal­i­ties such as Down syn­drome, “there are about 6,000 other ge­netic dis­or­ders which we cur­rently have a hard time to as­sess non­in­va­sively and as early,” said Wayne State as­so­ciate pro­fes­sor Sascha Drewlo, co-author of the study in Science Trans­la­tional Medicine. He calls de­fects caused by sin­gle gene mu­ta­tions “the big­gest gap” in pre­na­tal test­ing.

To­day’s main op­tions are in­va­sive tests - am­nio­cen­te­sis and CVS, or chori­onic vil­lus sam­pling - that an­a­lyze a sam­ple of am­ni­otic fluid or pla­centa tis­sue. They carry a small risk of mis­car­riage. Am­nio­cen­te­sis typ­i­cally is per­formed around 15 weeks and CVS around 10 weeks.

A blood test of­fers a slightly ear­lier and non­in­va­sive op­tion by an­a­lyz­ing small amounts of fe­tal DNA that float in a preg­nant woman’s blood­stream. Wor­ri­some re­sults are sup­posed to be ver­i­fied by an in­va­sive test. Early di­ag­no­sis isn’t just about de­cid­ing whether to go for­ward with a preg­nancy but can af­fect pre­na­tal care and what care a baby might need at birth.

It turns out that a small num­ber of cells con­tain­ing DNA of the form­ing fe­tus are shed into a mom-to-be’s re­pro­duc­tive tract, where the scrape of a rou­tine Pap can col­lect them along with the woman’s own cer­vi­cal cells. They’re called tro­phoblasts, cells that start the pla­centa’s growth.

The first chal­lenge is to sep­a­rate those cells from mom’s. The Wayne State team, led by Drewlo and Pro­fes­sor D. Ran­dall Ar­mant, calls its method TRIC, for tro­phoblast re­trieval iso­la­tion from the cervix.

They tested the ap­proach in 20 preg­nant women who had Paps be­tween 5 weeks and 19 weeks ges­ta­tion. The re­searchers re­ported on Wed­nes­day that they could ex­tract the tro­phoblasts and ac­cu­rately map the DNA in­side, a step to iden­ti­fy­ing ge­netic dis­or­ders.

That’s not the only po­ten­tial use. The re­searchers also are ex­am­in­ing whether these cells may of­fer a warn­ing of brew­ing prob­lems with the pla­centa. The work is in­trigu­ing but still pre­lim­i­nary, said Dr. Ron­ald Wap­ner, a pre­na­tal screen­ing spe­cial­ist at Columbia Univer­sity.

Es­pe­cially this early in preg­nancy, “we have to make sure the cells you get are truly rep­re­sen­ta­tive of what’s go­ing on in the fe­tus,” he said, some­thing larger tests could de­ter­mine.

Dr. Cather­ine Spong of the Na­tional In­sti­tutes of Health, which helped fund the study, called the re­search “re­ally nicely done and help­ful to the field,” but echoed that cau­tion. The pla­centa and fe­tus both orig­i­nate from the fer­til­ized egg and thus share a ge­netic pro­file, but oc­ca­sion­ally an ab­nor­mal­ity oc­curs only in the pla­centa. Spong said as the re­search con­tin­ues, it might shed more light on pla­centa for­ma­tion. — AP

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