This LDLR mutation in exon 4 constitutes a cysteine substitution. The cysteine of codon 163 is the last aminoacid of the IV repeat region of the ligand binding domain of the LDL receptor. and is a highly conserved residue. This allows us to speculate that this mutation produces an allele that interferes with the binding of the ligand to the receptor ( Class 3 Phenotype). However, this mutation may also have an effect on the transport of the protein between the endoplasmatic reticulum and the Golgi apparatus producing a class 2 Phenotype. The fact that this transition occurs in a highly conserved residue contributes to our belief that it is a disease-causing sequence variant. In the same family we were able to identify another novel single aminoacid substitution (C255Y) in exon 6 of the LDL receptor gene.This version is archived in the Arab International University (AIU) repository for open access and dissemination purposes. The content of this paper has not been modified from the original publication.For more information, please visit the official repository of Arab International University (AIU):https://aiu.edu.sy