Advanced renal insufficiency in a 34-year-old man with Lowe syndrome

Kidney-differentiated cells derived from Lowe Syndrome patient's iPSCs show ciliogenesis defects and Six2 retention at the Golgi complex

Lowe syndrome is an X-linked condition characterized by congenital cataracts, neurological abnormalities and kidney malfunction. This lethal disease is caused by mutations in the OCRL1 gene, which encodes for the phosphatidylinositol 5-phosphatase Ocrl1. While in the past decade we witnessed substantial progress in the identification and characterization of LS patient cellular phenotypes, many of these studies have been performed in knocked-down cell lines or patient's cells from accessible cell types such as skin fibroblasts, and not from the organs affected. This is partially due to the limited accessibility of patient cells from eyes, brain and kidneys. Here we report the preparation of induced pluripotent stem cells (iPSCs) from patient skin fibroblasts and their reprogramming into kidney cells. These reprogrammed kidney cells displayed primary cilia assembly defects similar to those described previously in cell lines. Additionally, the transcription factor and cap mesenchyme marker Six2 was substantially retained in the Golgi complex and the functional nuclear-localized fraction was reduced. These results were confirmed using different batches of differentiated cells from different iPSC colonies and by the use of the human proximal tubule kidney cell line HK2. Indeed, OCRL1 KO led to both ciliogenesis defects and Six2 retention in the Golgi complex. In agreement with Six2's role in the suppression of ductal kidney lineages, cells from this pedigree were over-represented among patient kidney-reprogrammed cells. We speculate that this diminished efficacy to produce cap mesenchyme cells would cause LS patients to have difficulties in replenishing senescent or damaged cells derived from this lineage, particularly proximal tubule cells, leading to pathological scenarios such as tubular atrophy.

Ocular Pathology of Oculocerebrorenal Syndrome of Lowe: Novel Mutations and Genotype-Phenotype Analysis

Mutations in the OCRL1 gene result in the oculocerebrorenal syndrome of Lowe, with symptoms including congenital bilateral cataracts, glaucoma, renal failure, and neurological impairments. OCRL1 encodes an inositol polyphosphate 5-phosphatase which preferentially dephosphorylates phosphatidylinositide 4,5 bisphosphate (PI(4,5)P₂). We have identified two novel mutations in two unrelated Lowe syndrome patients with congenital glaucoma. Novel deletion mutations are detected at c.739-742delAAAG in Lowe patient 1 and c.1595-1631del in Lowe patient 2. End stage glaucoma in patient 2 resulted in the enucleation of the eye, which on histology demonstrated corneal keloid, fibrous infiltration of the angle, ectropion uvea, retinal gliosis, and retinal ganglion cell loss. We measured OCRL protein levels in patient keratinocytes and found that Lowe 1 patient cells had significantly reduced OCRL protein as compared to the control keratinocytes. Genotype-phenotype correlation of OCRL1 mutations associated with congenital glaucoma revealed clustering of missense and deletion mutations in the 5-phosphatase domain and the RhoGAP-like domain. In conclusion, we report novel OCRL1 mutations in Lowe syndrome patients and the corresponding histopathologic analysis of one patient’s ocular pathology.

[Lowe syndrome revealed by prenatal diagnosis of congenital cataract with brain abnormalities]

Congenital cataract is a rare disease whose incidence is estimated to 0.5% of birth in France. A study of the literature shows that congenital cataract is idiopathic in 50% of cases, hereditary forms representing 25% of cases. Other causes of congenital cataract are represented by viral embryofoetopathies acquired during pregnancy, metabolic disorders and chromosomal aberrations within the scope of malformative syndromes. The authors report the case of a neonatal diagnosis of Lowe syndrome suspected by the discovery of bilateral cataract initially isolated. The morphological exploration was completed by secondary brain abnormalities (periventricular lesions). The etiological prenatal exploration was negative. Lowe syndrome is a rare cause of antenatal cataract, which so far only one case has been reported.

Whole-exome sequencing and homozygosity analysis implicate depolarization-regulated neuronal genes in autism

Although autism has a clear genetic component, the high genetic heterogeneity of the disorder has been a challenge for the identification of causative genes. We used homozygosity analysis to identify probands from nonconsanguineous families that showed evidence of distant shared ancestry, suggesting potentially recessive mutations. Whole-exome sequencing of 16 probands revealed validated homozygous, potentially pathogenic recessive mutations that segregated perfectly with disease in 4/16 families. The candidate genes (UBE3B, CLTCL1, NCKAP5L, ZNF18) encode proteins involved in proteolysis, GTPase-mediated signaling, cytoskeletal organization, and other pathways. Furthermore, neuronal depolarization regulated the transcription of these genes, suggesting potential activity-dependent roles in neurons. We present a multidimensional strategy for filtering whole-exome sequence data to find candidate recessive mutations in autism, which may have broader applicability to other complex, heterogeneous disorders.

OCRL1 mutation in a boy with Dent disease, mild mental retardation, but without cataracts

BACKGROUND

Oculocerebrorenal (Lowe) syndrome is an X-linked multisystem disease characterized by renal proximal tubulopathy, mental retardation, and congenital cataracts. We present a 19-year-old boy who was found to have low molecular weight proteinuria, hypercalciuria, mild generalized hyperaminoaciduria and intermittent microscopic hematuria at the age of 3.

METHODS

Standard clinical and biochemical examinations and mutational analysis of the CLNC5 and OCRL1 gene were performed for the patient.

RESULTS

The patient fulfilled diagnostic criteria for Dent disease, but lacked mutation in CLCN5. Sequencing of candidate genes revealed a mutation in his OCRL1 gene, which encodes for enzyme PIP2 5-phosphatase. The enzyme was not detected by western blot analysis, and decreased activity of the enzyme PIP2 5-phosphatase was observed in cultured skin fibroblasts. The boy had only mild mental retardation, mildly elevated muscle enzymes, but no neurological deficit or congenital cataracts, which are typical for Lowe syndrome.

CONCLUSIONS

Children with Dent phenotype who lack CLCN5 mutation should be tested for OCRL1 mutation. OCRL1 mutations may present with mild clinical features and are not necessarily associated with congenital cataracts.

Clinical and laboratory features of Macedonian children with OCRL mutations

OCRL mutations, which are a hallmark of Lowe syndrome, have recently been found in patients with isolated renal phenotype (Dent-2 disease). In this report, we describe clinical and laboratory features in five Macedonian children with mutations in the OCRL gene. Children with a clinical diagnosis of Lowe syndrome or Dent disease underwent complete neurological and ophthalmological examination, imaging of the kidney and urinary tract, assessment of renal tubular function, and mutation analysis of the OCRL gene. Two children (18 months and 11 years, respectively) were diagnosed with Lowe syndrome on the basis of congenital cataracts, severe psychomotor retardation, and renal dysfunction. Both children had low molecular weight proteinuria (LMWP) and hypercalciuria, but not Fanconi syndrome. The older one had bilateral nephrolithiasis due to associated hypocitraturia and mild hyperoxaluria. Three children with asymptomatic proteinuria were diagnosed with Dent-2 disease; none had cataracts or neurological deficit. One child showed mild mental retardation. All had LMWP, hypercalciuria, and elevated enzymes (creatine phosphokinase, lactic dehydrogenase). All three children had an abnormal Tc-99m DMSA scan revealing poor visualization of the kidneys with a high radionuclide content in the bladder; none had nephrolithiasis or nephrocalcinosis. In conclusion, children with OCRL mutations may present with very mild phenotype (asymptomatic proteinuria with/without mild mental retardation) or severe classic oculocerebrorenal syndrome of Lowe. Elevated enzymes and abnormal results on the Tc-99m DMSA scan may be useful indicators for Dent-2 disease.

Dent-2 disease: a mild variant of Lowe syndrome

OBJECTIVE

To compare the renal and extra-renal phenotypes of patients classified as having Dent disease, Dent-2 disease, or Lowe syndrome.

STUDY DESIGN

Chart review of data from 93 patients with identified voltage-gated chloride channel and chloride/proton antiporter 5 gene and oculo-cerebro-renal syndrome of Lowe gene mutations observed by the authors, complemented with published data.

RESULTS

There was a wide overlap of renal symptoms. Nephrocalcinosis was more prevalent in Dent-1 disease, and renal tubular acidosis, aminoaciduria, and renal failure was more prevalent in patients with Lowe syndrome. Patients with Lowe syndrome were shorter than patients with Dent-1 disease, and patients with Dent-2 disease showed an intermediate phenotype. Three patients with Dent-2 disease had mild peripheral cataract, and 9 patients were noted to have some degree of mental retardation.

CONCLUSION

There is a phenotypic continuum within patients with Dent-2 disease and Lowe syndrome, suggesting that there are individual differences in the ability to compensate for loss of oculo-cerebro-renal syndrome of Lowe gene function.

Novel OCRL1 mutations in patients with the phenotype of Dent disease

BACKGROUND

Dent disease is an X-linked tubulopathy frequently caused by mutations affecting the voltage-gated chloride channel and chloride/proton antiporter ClC-5. A recent study showed that defects in OCRL1, encoding a phosphatidylinositol 4,5-bisphosphate 5-phosphatase (Ocrl) and usually found mutated in patients with Lowe syndrome, also can provoke a Dent-like phenotype (Dent 2 disease).

METHODS

We investigated 20 CLCN5-negative males from 17 families with a phenotype resembling Dent disease for defects in OCRL1.

RESULTS

In our complete series of 35 families with a phenotype of Dent disease, a mutation in the OCRL1 gene was detected in 6 kindreds. All were novel frameshift (Q70RfsX88 and T121NfsX122, detected twice) or missense mutations (I257T and R476W). None of our patients had cognitive or behavioral impairment or cataracts, 2 classic hallmarks of Lowe syndrome. All patients had mild increases in lactate dehydrogenase and/or creatine kinase levels, which rarely is observed in CLCN5-positive patients, but frequently found in patients with Lowe syndrome. To explain the phenotypic heterogeneity caused by OCRL1 mutations, we performed extensive data-bank mining and extended reverse-transcriptase polymerase chain reaction analysis, which provided no evidence for yet unknown (tissue-specific) alternative OCRL1 transcripts.

CONCLUSION

Mutations in the OCRL1 gene are found in approximately 23% of kindreds with a Dent phenotype. Defective protein sorting/targeting of Ocrl might be the reason for mildly elevated creatine kinase and lactate dehydrogenase serum concentrations in these patients and a clue to suspect Dent disease unrelated to CLCN5 mutations. It remains to be elucidated why the various OCRL1 mutations found in patients with Dent 2 disease do not cause cataracts.