11.   How they would act on news of a gene defect threatening their offspring depended on how grave the disease was predicted to be, she said.

12.   Most diseases occur when a pathogen or a gene defect causes a cell to make aberrant proteins.

13.   One suggestion has been that these gene defects might render the mice incapable of smelling their young.

14.   Scientists have found a gene defect that causes a rare, lethal disease in boys, rendering them helpless to attack from a virus that most people harbor harmlessly.

15.   Still, in both studies, researchers found small groups of people with the gene defect who remained uninfected for years despite thousands of risky sexual encounters.

16.   The paper from the Baylor scientists is the first to describe the gene defect for this disorder.

17.   The researchers knocked out the bax gene in mouse embryos, creating a gene defect that seemed to produce no harmful effects in the animals later in life.

18.   To complicate matters further, the same gene defect may not behave the same way in all families.

19.   Salk lead researcher Dr. Carrolee Barlow bred mice with the A-T gene defect and examined cells from the cerebellum, the brain region that controls movement.

20.   To reverse the gene defect, doctors at Necker Hospital in Paris drew bone marrow from the boys.