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Mysterious birth defects: No answers, only questions, experts say

Shirley Dufault, left, comforts Jocelyn Robles at the end of a public meeting in Sunnyside, Washington, on Tuesday. Robles is 15 weeks pregnant and her baby has a rare and fatal birth defect, anencephaly. Dufault's son was born with anencephaly in 1977.
Shirley Dufault, left, comforts Jocelyn Robles at the end of a public meeting in Sunnyside, Washington, on Tuesday. Robles is 15 weeks pregnant and her baby has a rare and fatal birth defect, anencephaly. Dufault's son was born with anencephaly in 1977.James Cheng / for NBC News