Lathosterolosis: A Relatively Mild Case with Cataracts and Learning Difficulties.

Lathosterolosis is a rare defect of cholesterol synthesis. Only four previous cases have been reported, two of whom were siblings. We report a fifth patient, with a relatively mild phenotype. He presented at 5 years of age with bilateral posterior cataracts, which were managed with lensectomies and intraocular lens implants. He also had learning difficulties, with a full-scale IQ of 64 at 11 years of age. His head circumference is between the 0.4th and 2nd centiles, and he has mild hypotonia and subtle dysmorphism (a high-arched palate, anteverted nostrils, long philtrum and clinodactyly of toes). The diagnosis was established after sequencing a panel of genes associated with cataracts, which revealed compound heterozygous SC5D mutations: c.479C>G p.(Pro160Arg) and c.630C>A p.(Asp210Glu). The plasma lathosterol concentration was markedly raised at 219.8 μmol/L (control range 0.53-16.0), confirming the diagnosis. The c.630C>A p.(Asp210Glu) mutation has been reported in one previous patient, who also had a relatively mild phenotype (Ho et al., JIMD Rep 12:129-134, 2014). The mutation leads to a relatively conservative amino acid substitution, consistent with some residual enzyme activity. Our patient's family did not notice any benefit from treatment with simvastatin. In summary, milder patients with lathosterolosis may present with learning difficulties, cataracts and very subtle dysmorphism. The diagnosis will be missed unless plasma sterols are analysed or relevant genes sequenced.