Whole-genome sequencing revealed an interstitial deletion encompassing OCRL and SMARCA1 gene in a patient with Lowe syndrome

Prenatal ultrasound findings of X-linked congenital cataracts: case report and description of a novel variant

Congenital cataracts, an important cause of permanent visual loss in children, are predominantly caused by hereditary factors. Genetic variants reportedly cause approximately 50% of congenital cataracts. The literature mainly describes cases of autosomal dominant inheritance diagnosed after birth, and minimal information is available concerning the prenatal diagnosis of X-linked congenital cataracts. Prenatal ultrasound is the primary method for diagnosis of congenital cataracts, whereas the diagnostic value of prenatal genetic testing remains controversial; however, such testing is reportedly essential for determination of disease etiology. Here, we describe a 33-year-old multigravida woman with a singleton pregnancy who was referred to our center at 24 weeks for routine prenatal examination; ultrasound imaging revealed bilateral cataracts in the male fetus. Genetic testing revealed a pathogenic variant in exon 11 of the OCRL inositol polyphosphate-5-phosphatase (OCRL) gene in the fetal sample, with the potential to cause the X-linked recessive genetic disease Dent disease 2 (Online Mendelian Inheritance in Man [OMIM]: 300555) or the X-linked recessive genetic disorder Lowe's syndrome (OMIM: 309000). We provide a comprehensive family history and our findings in a gross examination of the stillborn fetus. So, ultrasound imaging provides important information that can guide the diagnosis of congenital cataracts. When congenital cataracts are detected by prenatal ultrasound, a detailed family history should be obtained. We recommend genetic testing of the fetus and the family members to determine the etiology.

Genotype Phenotype Correlation in Dent Disease 2 and Review of the Literature: OCRL Gene Pleiotropism or Extreme Phenotypic Variability of Lowe Syndrome?

Dent disease is a rare X-linked renal tubulopathy due to CLCN5 and OCRL (DD2) mutations. OCRL mutations also cause Lowe syndrome (LS) involving the eyes, brain and kidney. DD2 is frequently described as a mild form of LS because some patients may present with extra-renal symptoms (ESs). Since DD2 is a rare disease and there are a low number of reported cases, it is still unclear whether it has a clinical picture distinct from LS. We retrospectively analyzed the phenotype and genotype of our cohort of 35 DD2 males and reviewed all published DD2 cases. We analyzed the distribution of mutations along the OCRL gene and evaluated the type and frequency of ES according to the type of mutation and localization in OCRL protein domains. The frequency of patients with at least one ES was 39%. Muscle findings are the most common ES (52%), while ocular findings are less common (11%). Analysis of the distribution of mutations revealed (1) truncating mutations map in the PH and linker domain, while missense mutations map in the 5-phosphatase domain, and only occasionally in the ASH-RhoGAP module; (2) five OCRL mutations cause both DD2 and LS phenotypes; (3) codon 318 is a DD2 mutational hot spot; (4) a correlation was found between the presence of ES and the position of the mutations along OCRL domains. DD2 is distinct from LS. The mutation site and the mutation type largely determine the DD2 phenotype.

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.

The Primary Cilium as a Therapeutic Target in Ocular Diseases

Primary cilia are microtubule-based cellular structures located on the surfaces of most mammalian cells and play important roles in detecting external stimuli, signal transduction, and cell cycle regulation. Primary cilia are also present in several structures of the eye, and their abnormal development or dysfunction can cause various ocular diseases. The rapid development of proteomics and metabolomics technologies have helped in the identification of many ocular disease-related proteins, some of which are dysregulated in primary cilia. This review focuses on ciliary dysregulation in a number of ocular diseases and discusses the potential of targeting primary cilia in gene and stem cell therapy for these diseases.

Whole-genome sequencing revealed an interstitial deletion encompassing OCRL and SMARCA1 gene in a patient with Lowe syndrome

Background

Lowe syndrome is a rare X‑linked syndrome that is characterized by involvement of the eyes, central nervous system, and kidneys. The aim of the present study was to determine the molecular basis of four patients with congenital cataract, infantile congenital hypotonia, and proximal renal tubular defect.

Methods

Four children who met the clinical manifestations of Lowe syndrome were enrolled in this study. Patients’ clinical information on eyes, central nervous system, kidneys, and family histories, etc., were reviewed and analyzed. After obtaining informed consent, we performed a mutation analysis of OCRL gene using direct sequencing. Because of failure of PCR amplification, low coverage shortread whole genome sequencing (CNVseq) analysis was performed on one proband. Real‐time PCR was subsequently performed to confirm the CNV that was detected from the CNVseq results.

Results

We identified three OCRL allelic variants, including two novel missense mutations (c.1423C>T/p.Pro475Ser, c.1502T>G/p.Ile501Ser) and one recurrent nonsense mutation (c.2464C>T/p.Arg822Ter). Various bioinformatic tools revealed scores associated with potential pathogenic effects for the two missense variants, and protein alignments revealed that both variants affected an amino acid highly conserved among species. Since deletion of the entire gene was suspected in a patient, CNVseq was used, identifying an interstitial deletion to approximately 190 kb, encompassing OCRL, and SMARCA1 gene. Moreover, the hemizygous CNV was confirmed by qPCR. Reviewing another case reported in the literature, we found that the deletion of OCRL and nearby genes may contribute to a more severe phenotype and premature death.

Conclusions

This is the first report of an interstitial deletion encompassing OCRL and SMARCA1 gene in Lowe syndrome. Our results expand the spectrum of mutations of the OCRL gene in Chinese population. Moreover, whole‐genome sequencing presents a comprehensive and reliable approach for detecting genomic copy number variation in patients or carriers in the family with rare inherited disorders.