Two distinct phenotypes of Dent disease-2 and Lowe syndrome are caused by oculocerebrorenal syndrome of Lowe (OCRL) abnormality. Previous genetic studies demonstrated that truncating variants in exons 1 to 7 results in Dent disease-2 and in exons 8 to 24, result in Lowe syndrome. Recently, we successfully identified a functional OCRL isoform, whose altered initiation codons (Met187 and Met206) in exon 8 can affect the OCRL-truncating variant phenotypes. However, the association between OCRL splicing variants and phenotypes is poorly understood. We performed a detailed splicing pattern analysis of previously reported 28 OCRL splicing variants obtained from the Human Gene Mutation Database. We assessed the variant consequences at the mRNA level using an in vitro splicing assay with a minigene system, and examined their compatibility with in silico algorithms and correlation with disease phenotypes. Aberrant splicing was confirmed in all 27 variants, except for 1, in which splicing could not be experimentally confirmed in the minigene system, and therefore could not be concluded with certainty. Splicing variants in OCRL exons 1 to 7 resulted in Dent disease-2, and in exons 9 to 24 resulted in Lowe syndrome. In 1 case, c.561-2 A > G in exon 8 demonstrated Dent disease-2. This study provides significant data on the pathogenicity of OCRL splicing variants and genotype-phenotype correlations. In c.561-2 A > G, the latter altered initiation codon of the OCRL isoform (Met206) was preserved, potentially indicating the Dent disease-2 phenotype. This result supports our recent finding regarding the altered initiation codons in exon 8 of the OCRL isoform.

Ultrasound biomicroscopy comparison of two infants with Lowe oculocerebrorenal syndrome, one with glaucoma and one without, found differences in corneal curvature, iris thickness, trabecular-iris angle, and lens morphology are potential glaucoma-associated features.

Löwe syndrome (the oculocerebrorenal syndrome of Löwe, OCRL, OMIM #309000, ORPHA: 534) is a very rare multisystem X-linked disorder characterized by ocular, kidney and nervous system anomalies. We present the first Bulgarian genetically confirmed patient with OCRL. The patient had facial dysmorphism, cryptorchidism, congenital cataracts, nystagmus, delayed physical and mental development, and poor nutritional status. He had severe rickets, metabolic acidosis, hypokalaemia, hypophosphataemia, and low IGF-1 levels at the age of three, in addition to his developmental delay. The molecular-genetic analysis reported a pathogenic variant c.1124A>G, p.H375R in the OCRL gene. This variant was inherited from the mother, who was a carrier. Following the diagnosis of OCRL, treatment with potassium citrate, phosphate, and calcitriol was initiated, along with an increase in caloric intake. Following general physical and biochemical improvement, therapy with rhGH started 4 years ago, and current results are presented. The patient with Löwe syndrome who was presented with a 6-year follow-up demonstrates the complexity of rare disease cases and the value of multidisciplinary care together with growth hormone treatment for better results in these patients.

T-cell acute lymphoblastic leukemia (T-ALL) is one of the deadliest and most aggressive hematological malignancies, but its pathological mechanism in controlling cell survival is not fully understood. Oculocerebrorenal syndrome of Lowe is a rare X-linked recessive disorder characterized by cataracts, intellectual disability, and proteinuria. This disease has been shown to be caused by mutation of oculocerebrorenal syndrome of Lowe 1 (OCRL1; OCRL), encoding a phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] 5-phosphatase involved in regulating membrane trafficking; however, its function in cancer cells is unclear. Here, we uncovered that OCRL1 is overexpressed in T-ALL cells, and knockdown of OCRL1 results in cell death, indicating the essential role of OCRL in controlling T-ALL cell survival. We show OCRL is primarily localized in the Golgi and can translocate to plasma membrane (PM) upon ligand stimulation. We found OCRL interacts with oxysterol-binding protein-related protein 4L, which facilitates OCRL translocation from the Golgi to the PM upon cluster of differentiation 3 stimulation. Thus, OCRL represses the activity of oxysterol-binding protein-related protein 4L to prevent excessive PI(4,5)P2 hydrolysis by phosphoinositide phospholipase C β3 and uncontrolled Ca2+ release from the endoplasmic reticulum. We propose OCRL1 deletion leads to accumulation of PI(4,5)P2 in the PM, disrupting the normal Ca2+ oscillation pattern in the cytosol and leading to mitochondrial Ca2+ overloading, ultimately causing T-ALL cell mitochondrial dysfunction and cell death. These results highlight a critical role for OCRL in maintaining moderate PI(4,5)P2 availability in T-ALL cells. Our findings also raise the possibility of targeting OCRL1 to treat T-ALL disease.

Lowe syndrome (LS) is a rare, X-linked disorder characterised by numerous symptoms affecting the brain, the eyes, and the kidneys. It is caused by mutations in the oculocerebrorenal syndrome of Lowe (OCRL) protein, a 5-phosphatase localised in different cellular compartments that dephosphorylates phosphatidylinositol-4,5-bisphosphate into phosphatidylinositol-4-monophosphate. Some patients with LS also have bleeding disorders, with normal to low platelet (PLT) count and impaired PLT function. However, the mechanism of PLT dysfunction in patients with LS is not completely understood. The main function of PLTs is to activate upon vessel wall injury and stop the bleeding by clot formation. PLT activation is accompanied by a shape change that is a result of massive cytoskeletal rearrangements. Here, we show that OCRL-inhibited human PLTs do not fully spread, form mostly filopodia, and accumulate actin nodules. These nodules co-localise with ARP2/3 subunit p34, vinculin, and sorting nexin 9. Furthermore, OCRL-inhibited PLTs have a retained microtubular coil with high levels of acetylated tubulin. Also, myosin light chain phosphorylation is decreased upon OCRL inhibition, without impaired degranulation or integrin activation. Taken together, these results suggest that OCRL contributes to cytoskeletal rearrangements during PLT activation that could explain mild bleeding problems in patients with LS.