A novel OCRL1 mutation in a patient with the mild phenotype of Lowe syndrome

Oculocerebrorenal syndrome of Lowe (OCRL, OMIM 309000), also known as Lowe syndrome, is a rare X-linked multisystem disorder characterized by congenital cataracts, mental retardation, and Fanconi syndrome of the kidney proximal tubules. Lowe syndrome is caused by mutations in the gene encoding a member of the inositol polyphosphate-5-phosphatase protein family (OCRL1) on chromosome Xq26.1. OCRL1 contains 24 exons and encodes a 105-kDa phosphatidylinositol (4,5) bisphosphate 5-phosphatase. An OCRL1 isoform generated by alternative splicing is predominantly expressed in brain, and localizes to the trans-Golgi network, lysosomes, and endosomes. Impaired inositol polyphosphate-5-phosphatase activity elevates phosphatidylinositol (4,5) bisphosphate levels that are required for vesicle trafficking within the Golgi apparatus, actin cytoskeleton remodeling closely associated with Golgi, and endosomal membrane trafficking. Accordingly, abnormalities in the actin cytoskeleton may influence the function of renal epithelial cells in patients with Lowe syndrome. OCRL1 mutations exist in about 95% of patients with Lowe syndrome, and new mutations occur in 32% affected males. We here describe a Japanese male with the mild phenotype of Lowe syndrome. Physical examination revealed mild congenital bilateral cataracts, mild mental disability, and short stature. Proteinuria was also mild with a high β2-microglobulinuria level. Nucleotide sequence analysis identified a hemizygous mutation (T-to-C transition) at nucleotide 2039 in exon 18 that substitutes Ser (TCT) for Phe (TTT) at amino acid position 680. This missense mutation is located outside the known catalytic domain that is encoded by exons 4 through 15. The present patient carries a novel OCRL1 mutation that is helpful for genetic counseling.