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Novel causative mutations in patients with Nance-Horan syndrome and altered localization of the mutant NHS-A protein isoform.

Sharma S, Burdon KP, Dave A, Jamieson RV, Yaron Y, Billson F, Van Maldergem L, Lorenz B, Gécz J, Craig JE - Mol. Vis. (2008)

Bottom Line: Truncating mutations were found in 6 out of 10 unrelated patients from four countries.No mutation was found in the gene in four patients.Two disease-causing mutations (R134fs and R901X) and an artificial mutation (T1357fs) resulted in premature truncation of the NHS-A protein.

View Article: PubMed Central - PubMed

Affiliation: Department of Ophthalmology, Flinders University, Bedford Park, South Australia, Australia. shiwani.sharma@flinders.edu.au

ABSTRACT

Purpose: Nance-Horan syndrome is typically characterized by severe bilateral congenital cataracts and dental abnormalities. Truncating mutations in the Nance-Horan syndrome (NHS) gene cause this X-linked genetic disorder. NHS encodes two isoforms, NHS-A and NHS-1A. The ocular lens expresses NHS-A, the epithelial and neuronal cell specific isoform. The NHS-A protein localizes in the lens epithelium at the cellular periphery. The data to date suggest a role for this isoform at cell-cell junctions in epithelial cells. This study aimed to identify the causative mutations in new patients diagnosed with Nance-Horan syndrome and to investigate the effect of mutations on subcellular localization of the NHS-A protein.

Methods: All coding exons of NHS were screened for mutations by polymerase chain reaction (PCR) and sequencing. PCR-based mutagenesis was performed to introduce three independent mutations in the NHS-A cDNA. Expression and localization of the mutant proteins was determined in mammalian epithelial cells.

Results: Truncating mutations were found in 6 out of 10 unrelated patients from four countries. Each of four patients carried a novel mutation (R248X, P264fs, K1198fs, and I1302fs), and each of the two other patients carried two previously reported mutations (R373X and R879X). No mutation was found in the gene in four patients. Two disease-causing mutations (R134fs and R901X) and an artificial mutation (T1357fs) resulted in premature truncation of the NHS-A protein. All three mutant proteins failed to localize to the cellular periphery in epithelial cells and instead were found in the cytoplasm.

Conclusions: This study brings the total number of mutations identified in NHS to 18. The mislocalization of the mutant NHS-A protein, revealed by mutation analysis, is expected to adversely affect cell-cell junctions in epithelial cells such as the lens epithelium, which may explain cataractogenesis in Nance-Horan syndrome patients. Mutation analysis also shed light on the significance of NHS-A regions for its localization and, hence, its function at epithelial cell junctions.

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Chromatograms of identified mutations. In each case, the wild type sequence is shown above the mutated sequence for each patient. A shows the 3596insA in patient 101; B shows the C2635T in patient 105; C shows the C1117T in patient 120; D shows the 3908del11bp in patient 122; E shows the 792delA in patient 127; and F shows the C742T in patient 135.
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f1: Chromatograms of identified mutations. In each case, the wild type sequence is shown above the mutated sequence for each patient. A shows the 3596insA in patient 101; B shows the C2635T in patient 105; C shows the C1117T in patient 120; D shows the 3908del11bp in patient 122; E shows the 792delA in patient 127; and F shows the C742T in patient 135.

Mentions: Individual 101, a 19-year-old male from Germany, presented with major ophthalmic features of congenital cataract and secondary glaucoma. He had microcornea and nystagmus at three months of age and presented with strabismus and microphthalmia in childhood. His mother had nuclear cataract with cone-shaped sutural lens opacity. Both the index case and his mother were found to have a previously undescribed single base insertion 3596insA in exon 6, coding for K1198 frameshift (Figure 1A). This mutation results in the incorporation of four aberrant amino acids, terminating at position 1203.


Novel causative mutations in patients with Nance-Horan syndrome and altered localization of the mutant NHS-A protein isoform.

Sharma S, Burdon KP, Dave A, Jamieson RV, Yaron Y, Billson F, Van Maldergem L, Lorenz B, Gécz J, Craig JE - Mol. Vis. (2008)

Chromatograms of identified mutations. In each case, the wild type sequence is shown above the mutated sequence for each patient. A shows the 3596insA in patient 101; B shows the C2635T in patient 105; C shows the C1117T in patient 120; D shows the 3908del11bp in patient 122; E shows the 792delA in patient 127; and F shows the C742T in patient 135.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2571945&req=5

f1: Chromatograms of identified mutations. In each case, the wild type sequence is shown above the mutated sequence for each patient. A shows the 3596insA in patient 101; B shows the C2635T in patient 105; C shows the C1117T in patient 120; D shows the 3908del11bp in patient 122; E shows the 792delA in patient 127; and F shows the C742T in patient 135.
Mentions: Individual 101, a 19-year-old male from Germany, presented with major ophthalmic features of congenital cataract and secondary glaucoma. He had microcornea and nystagmus at three months of age and presented with strabismus and microphthalmia in childhood. His mother had nuclear cataract with cone-shaped sutural lens opacity. Both the index case and his mother were found to have a previously undescribed single base insertion 3596insA in exon 6, coding for K1198 frameshift (Figure 1A). This mutation results in the incorporation of four aberrant amino acids, terminating at position 1203.

Bottom Line: Truncating mutations were found in 6 out of 10 unrelated patients from four countries.No mutation was found in the gene in four patients.Two disease-causing mutations (R134fs and R901X) and an artificial mutation (T1357fs) resulted in premature truncation of the NHS-A protein.

View Article: PubMed Central - PubMed

Affiliation: Department of Ophthalmology, Flinders University, Bedford Park, South Australia, Australia. shiwani.sharma@flinders.edu.au

ABSTRACT

Purpose: Nance-Horan syndrome is typically characterized by severe bilateral congenital cataracts and dental abnormalities. Truncating mutations in the Nance-Horan syndrome (NHS) gene cause this X-linked genetic disorder. NHS encodes two isoforms, NHS-A and NHS-1A. The ocular lens expresses NHS-A, the epithelial and neuronal cell specific isoform. The NHS-A protein localizes in the lens epithelium at the cellular periphery. The data to date suggest a role for this isoform at cell-cell junctions in epithelial cells. This study aimed to identify the causative mutations in new patients diagnosed with Nance-Horan syndrome and to investigate the effect of mutations on subcellular localization of the NHS-A protein.

Methods: All coding exons of NHS were screened for mutations by polymerase chain reaction (PCR) and sequencing. PCR-based mutagenesis was performed to introduce three independent mutations in the NHS-A cDNA. Expression and localization of the mutant proteins was determined in mammalian epithelial cells.

Results: Truncating mutations were found in 6 out of 10 unrelated patients from four countries. Each of four patients carried a novel mutation (R248X, P264fs, K1198fs, and I1302fs), and each of the two other patients carried two previously reported mutations (R373X and R879X). No mutation was found in the gene in four patients. Two disease-causing mutations (R134fs and R901X) and an artificial mutation (T1357fs) resulted in premature truncation of the NHS-A protein. All three mutant proteins failed to localize to the cellular periphery in epithelial cells and instead were found in the cytoplasm.

Conclusions: This study brings the total number of mutations identified in NHS to 18. The mislocalization of the mutant NHS-A protein, revealed by mutation analysis, is expected to adversely affect cell-cell junctions in epithelial cells such as the lens epithelium, which may explain cataractogenesis in Nance-Horan syndrome patients. Mutation analysis also shed light on the significance of NHS-A regions for its localization and, hence, its function at epithelial cell junctions.

Show MeSH
Related in: MedlinePlus