Four FH siblings were found to be compound heterozygotes for 2 LDLR mutations.

They carried a known missense mutation and a minute deletion in exon 8/intron 8 junction.

The deletion causes an in-frame deletion of 17 amino acids in the LDLR protein.

Two siblings with a less severe phenotype were carriers of a rare missense apoB variant.

This rare missense apoB variant may have an LDL-lowering effect.