Supplementary Material for: New Homozygous Missense MSMO1 Mutation in Two Siblings with SC4MOL Deficiency Presenting with Psoriasiform Dermatitis

Sterol-C4-methyl oxidase (SC4MOL) deficiency was recently described as an autosomal recessive cholesterol biosynthesis disorder caused by mutations in the MSMO1 (sometimes also referred to as SC4MOL) gene. To date, 5 patients from 4 unrelated families with SC4MOL deficiency have been reported. Diagnosis can be challenging as the biochemical accumulation of methylsterols can affect global development and cause skin and ocular pathology. Herein, we describe 2 siblings from a consanguineous Turkish family with SC4MOL deficiency presenting with psoriasiform dermatitis, ocular abnormalities (nystagmus, optic hypoplasia, myopia, and strabismus), severe intellectual disability, and growth and motor delay. We undertook whole-exome sequencing and identified a new homozygous missense mutation c.81A>C; p.Asn27Thr in MSMO1. Segregation analysis in all available family members confirmed recessive inheritance of the mutation. The siblings were treated with a combination of oral and topical statin and cholesterol which resulted in clinical improvement. This study demonstrates how genomics-based diagnosis and therapy can be helpful in clinical practice.