Novel OCRL mutations in Chinese children with Lowe syndrome

Novel pathogenic OCRL mutations and genotype-phenotype analysis of Chinese children affected by oculocerebrorenal syndrome: two cases and a literature review

BACKGROUND

Oculocerebrorenal syndrome of Lowe is a rare X-linked disorder characterized by congenital cataracts, mental retardation, and proximal tubulopathy. This condition is caused by a mutation of OCRL gene (located at chromosome Xq26.1), which encodes an inositol polyphosphate 5-phosphatase.

CASE PRESENTATION

We identified two novel OCRL mutations in two unrelated Chinese boys, each with a severe phenotype of Lowe syndrome. A novel de novo deletion (hemizygous c.659_662delAGGG, p.E220Vfs*29) was present in patient 1 and a novel splicing mutation (hemizygous c.2257-2A > T) that was maternally inherited was present in patient 2. A renal biopsy in patient 2 indicated mild mesangial proliferative glomerulonephritis, mild focal mononuclear cells infiltration, and interstitial focal fibrosis. Moreover, renal expression of OCRL-1 protein in patient 2 was significantly reduced compared to a control patient with thin basement membrane disease.

CONCLUSIONS

This study reports two novel OCRL variants associated with severe ocular and neurologic deficiency, despite only mild renal dysfunction. Based on our two patients and a literature review, the genotype-phenotype correlation of OCRL mutations with this severe phenotype of Lowe syndrome suggest a possible clustering of missense, deletion, and nonsense mutations in the 5-phosphatase domain and Rho-GAP domain in the Chinese population.

A novel CLCN5 mutation in a Chinese boy with Dent's disease

BACKGROUND

Dent's disease is a rare X-linked recessive hereditary disease caused by mutations in either the CLCN5 or OCRL1 genes. This disease is characterized by manifestations of proximal renal tubule dysfunction associated with low molecular weight proteinuria (LMWP), hypercalciuria, nephrocalcinosis, nephrolithiasis, and progressive renal failure.

METHODS

We report a Chinese boy with Dent's disease, clinically diagnosed by LMWP and hypercalciuria. Genetic analysis was made of the CLCN5 and OCRL1 genes. Related studies were also reviewed.

RESULTS

A splice site mutation IVS6, +2T>C of the CLCN5 gene was revealed in this case, and it was not reported previously.

CONCLUSIONS

Clinical and genetic analysis is valuable for the diagnosis of Dent's disease. A novel mutation in the CLCN5 gene was identified in our patient.

Structural basis for phosphoinositide substrate recognition, catalysis, and membrane interactions in human inositol polyphosphate 5-phosphatases

SHIP2, OCRL, and INPP5B belong to inositol polyphosphate 5-phophatase subfamilies involved in insulin regulation and Lowes syndrome. The structural basis for membrane recognition, substrate specificity, and regulation of inositol polyphosphate 5-phophatases is still poorly understood. We determined the crystal structures of human SHIP2, OCRL, and INPP5B, the latter in complex with phosphoinositide substrate analogs, which revealed a membrane interaction patch likely to assist in sequestering substrates from the lipid bilayer. Residues recognizing the 1-phosphate of the substrates are highly conserved among human family members, suggesting similar substrate binding modes. However, 3- and 4-phosphate recognition varies and determines individual substrate specificity profiles. The high conservation of the environment of the scissile 5-phosphate suggests a common reaction geometry for all members of the human 5-phosphatase family.