Familial cases of Norrie disease detected by copy number analysis

Abstract

Purpose: Norrie disease (ND, MIM#310600) is an X-linked disorder characterized by severe vitreoretinal dysplasia at birth. We report the results of causative NDP gene analysis in three male siblings with Norrie disease and describe the associated phenotypes.

Methods: Three brothers with suspected Norrie disease and their mother presented for clinical examination. After obtaining informed consent, DNA was extracted from the peripheral blood of the proband, one of his brothers and his unaffected mother. Exons 1-3 of the NDP gene were amplified by polymerase chain reaction (PCR), and direct sequencing was performed. Multiplex ligation-dependent probe amplification (MLPA) was also performed to search for copy number variants in the NDP gene.

Results: The clinical findings of the three brothers included no light perception, corneal opacity, shallow anterior chamber, leukocoria, total retinal detachment and mental retardation. Exon 2 of the NDP gene was not amplified in the proband and one brother, even when the PCR primers for exon 2 were changed, whereas the other two exons showed no mutations by direct sequencing. MLPA analysis showed deletion of exon 2 of the NDP gene in the proband and one brother, while there was only one copy of exon 2 in the mother.

Conclusion: Norrie disease was diagnosed in three patients from a Japanese family by clinical examination and was confirmed by genetic analysis. To localize the defect, confirmation of copy number variation by the MLPA method was useful in the present study.