Louisiana Code:
"Art. 90. Impediments of relationship
The following persons, whether legitimate or illegitimate, may not contract marriage with each other:
Ascendants and descendants. Collaterals within the fourth degree, whether of the whole or of the half blood.
The impediment exists whether the persons are related by consanguinity or by adoption. Nevertheless, persons related by adoption, though not by blood, in the
collateral line within the fourth degree may marry each other if they obtain judicial authorization in writing to do so."