The genetic basis for BLSII is not due to defects in the MHC II genes themselves. The genetic basis is the result of mutations in genes that code for proteins (transcription factors) that normally regulate the expression (gene transcription) of the MHC II genes.
The genetic basis of BLSII is not due to errors in the MHC II genes themselves; rather, it's caused by mutations in genes that code for proteins responsible for regulating the expression (gene transcription) of the MHC II genes.