Smith-Lemli-Opitz syndrome: Objective assessment of facial phenotype
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Smith-Lemli-Opitz syndrome (SLOS), is an autosomal recessive condition caused by cholesterol synthesis deficiency which results in a wide phenotypic spectrum which includes multiple malformations, distinctive facial appearance, and intellectual disability. This anthropometric and observational study was carried out to define the key facial characteristics of individuals with SLOS and to evaluate evolution of the facial phenotype with age. Clinical photographs were obtained on 51 subjects with SLOS and standardized facial anthropometry was performed on 42; the ages ranged from 6 months to 20 years. For each individual, 22 standardized cranial and facial measurements were obtained and compared to published age- and sex-matched controls. Craniofacial pattern profiles were compared between sexes, various age groups, plasma cholesterol concentration at the time of diagnosis, and physical severity score. Mean-Z, a measurement of overall facial size, and craniofacial variability index (CVI), a summary anthropometric measure of craniofacial deviation from the norm, were calculated and compared according to methods published previously. A characteristic craniofacial pattern profile was universally present: narrow forehead, brachycephaly, short palpebral fissures, short nasal ridge, anteverted nares, flat face, normal jaw width, and retrognathia. The facial measurements of subjects with SLOS had higher deviations from the norm with mean CVI of 2.11; SD = 0.47 (controls: Mean = 0.76, SD = 0.19; <0.0001) than age- and sex-matched controls. Their faces were also smaller than controls: 70% of subjects had mean-Z values 2 SD below the mean for controls; average Z-score was -1.64; SD = 0.85 (controls: mean = 0, SD = 0.64; <0.0001). There were no significant differences in the craniofacial pattern profile between the sexes or clinical severity as measured by either plasma cholesterol level at the time of diagnosis or the physical severity score. Patients with a lower weight at the time of assessment and patients with higher physical severity score had higher CVI measures (P < 0.001 and P < 0.002, respectively), suggesting that the degree of deviation from craniofacial norms is a function of the overall physical severity.
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