Is it permissible, from an Islamic and health perspective, and for the sake of future generations, to marry a girl who carries the thalassemia trait, knowing that the suitor is healthy, and should her condition be concealed from the family?

We do not know the true nature of the mentioned disease, and specialized doctors must be consulted.

Proceeding with marriage is permissible in principle, but if doctors confirm that the disease is transmitted to children or prevents conception, then it is preferable not to marry her, because procreation is desired in Sharia.

Al-Shafi'i said: "Leprosy and vitiligo, as claimed by those knowledgeable in medicine, are contagious. Hardly anyone's soul is content to have intercourse with someone who has it, nor is any woman's soul content with that from him. As for the child, it rarely escapes, and if it escapes, its offspring will inherit it. We ask Allah for well-being."

This indicates considering the child's future condition and that one should not strive for something that Allah makes a cause for their illness. And Allah knows best.