 This means the defective gene responsible for the disorder is located on an autosome (chromosome 2 is an autosome), and two copies of the defective gene (one inherited from each parent) are required in order to be born with the disorder.The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder.Elevated levels of serum cholestanol are diagnostic of CTX.