Patients with Smith-Lemli-Opitz (SLO) syndrome exhibit many clinical features including mental retardation, an unusual facial appearance, genital abnormalities, and syndactyly (fusion of the digits)....

Patients with Smith-Lemli-Opitz (SLO) syndrome exhibit many clinical features including mental retardation, an unusual facial appearance, genital abnormalities, and syndactyly (fusion of the digits). Patients with SLO tend to be similar in their features. SLO is an autosomal recessive condition. All heterozygotes will have expression. There is only one gene known to be responsible for this condition. This condition shows

A. highly variable phenotype.

B. locus heterogeneity.

C. pleiotropism.

D. thresholding.

E. Lyonization.