Case report: A case of Norrie disease due to deletion of the entire coding region of NDP gene

Novel mutation in the NDP gene associated with Norrie disease in a Chinese pedigree

PURPOSE

Norrie disease (ND) is a rare X-linked recessive disorder characteristic of early childhood blindness. While several mutations in the NDP gene have been reported as causative for ND, the genetic etiology remains unknown for many patients. This study aims to describe a novel mutation and explore the clinical manifestations in a Chinese family with two affected males.

METHODS

Exome sequencing (ES) was employed to identify the causative gene in a four-generation pedigree. Sanger sequencing was subsequently utilized to validate the mutation detected by ES in additional family members. Ophthalmologic examination and diagnostic imaging relevant to ND were conducted.

RESULTS

The proband (IV:2), an 8-month-old male infant, presented with binocular retinal detachment. DNA sequencing revealed a novel heterozygous missense mutation (c.174G>C) within the NDP gene in the proband. This mutation affected highly conserved residues and was predicted to disrupt the normal protein structure. Furthermore, the variant co-segregated with the disease phenotypes within the family.

CONCLUSIONS

Our findings identified a novel missense mutation in the NDP gene associated with Norrie disease in China, expanding the mutation spectrum associated with ND. This discovery holds diagnostic, prognostic, and genetic counseling implications for affected individuals.

Ocular Manifestations in Patients with Sensorineural Hearing Loss

Identification of ocular manifestations in patients with sensorineural hearing loss (SNHL) can have a large impact on the outcome and treatment of pediatric patients. Due to the common co-incidence of ocular manifestations and SNHL in children, both ophthalmologic and hearing loss screening and routine examinations must be conducted to minimize adverse outcomes and worsening of pathology. Early evaluation and diagnosis is imperative for intervention and further development of the patient. Co-incidence requires a thorough evaluation that includes a comprehensive history, examination, and diagnostic testing. In this article, a literature review was conducted to analyze the presentations of various diseases and syndromes, such as Alport Syndrome, Waardenburg Syndrome, Norrie Disease, Usher Disease, Stickler Syndrome, Marfan Syndrome, Congenital Rubella, and Hereditary Optic Neuropathies. We divided the various ocular pathologies into anterior and posterior segment presentations and associated systemic findings for better understanding. Additionally, this review aims to include an update on the management of patients with both ocular and hearing loss manifestations.

Next-generation sequencing reveals a case of Norrie disease in a child with bilateral ocular malformation

A Norrie disease protein gene (NDP) variant, c.174 + 1G > A, was found in a Chinese family through next-generation sequencing and verified with Sanger sequencing. A case of Norrie disease was reported in the first child, and the symptoms were consistent with the results of gene sequencing. The child’s mother, who was pregnant at the time, was found to be a carrier of the identified pathogenic variant. To determine if the fetus carried the same disease-causing variant, prenatal examination and prenatal diagnosis were conducted. The fetus had biocular vitreous abnormalities and complete retinal abnormalities. Genetic testing showed that the fetus had maternally inherited the NDP gene variant found in the proband. It was concurrently confirmed that the NDP gene variant led to the deletion of 246 bp at the 3′ end of exon 2, resulting in the deletion of the initiation codon and the occurrence of disease. Our study suggests that the diagnosis of rare diseases through next-generation sequencing, combined with prenatal ultrasound and prenatal diagnosis, can help families with known familial genetic diseases. Furthermore, the findings of this study broaden the known genetic spectrum of Norrie disease.

Ocular findings and genomics of X-linked recessive disorders: A review

Advent of new sequencing technologies and modern diagnostic procedures has opened the door for a deeper understanding of disorders about which little was known previously. Discovery of novel genes, new genetic variants in previously known genes and better techniques of functional validation has immensely contributed to unraveling the molecular basis of genetic disorders. Availability of knockout animal models like the zebrafish and gene editing tools like CRISPR-Cas9 has elucidated the function of many new genes and helped us to better understand the functional consequences of various gene defects. This has also led to better diagnosis and therapeutic interventions. In this context, a good body of research work has been done on X-linked recessive disorders with ocular findings. This review will focus on ocular and genetic findings of these rare disorders. To our knowledge, this is the first comprehensive review encompassing ocular and genomic spectrum of X-linked recessive disorders.