If some day they find a "gay gene" and can prove that some people are born that way, it wouldn't force orthodox Christians to change or amend any doctrine. We are all born sinners and deserving of God's eternal wrath.

Though included along with idolaters, fornicators, murderers, and theives among those who "will not inherit the kingdom of God (1st Corinthians 6:9)," it is also clear from that passage of Scripture that God forgives and washes away the stains from even homosexual sin:

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Such were some of you; but you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus Christ and in the Spirit of our God (1st Corinthians 6:11).