All states also set a threshold for flagging elevated IRT to prompt molecular testing of cystic fibrosis transmembrane conductance regulator (CFTR) gene variants as a second-line screen.

It occurs when the so-called CFTR protein is not made or not made ... Mutations may be unknown because of a lack of genetic testing in places such as developing nations, or understudied because ...

It occurs when the so-called CFTR protein is not made or not made ... Mutations may be unknown because of a lack of genetic testing in places such as developing nations, or understudied because ...