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A Chinese family with Oguchi's disease due to compound heterozygosity including a novel deletion in the arrestin gene.

Huang L, Li W, Tang W, Zhu X, Ou-Yang P, Lu G - Mol. Vis. (2012)

Bottom Line: No mutations were found in the GRK1 gene.A heterozygous nonsense Arg193stop (R193X) mutation was found in the SAG gene in the patient and the unaffected mother.No pathogenic SAG mutations were found in the unaffected father. qPCRs showed a heterozygous deletion encompassing exon 2 of the SAG gene in the patient and the unaffected father.

View Article: PubMed Central - PubMed

Affiliation: Institute of Reproductive and Stem Cell Engineering, Central South University, Changsha, PR China.

ABSTRACT

Purpose: Oguchi's disease is a rare autosomal recessive disease and known to be caused by mutations in the rhodopsin kinase (GRK1) gene or the arrestin (SAG) gene. SAG contains 16 exons and encodes a protein with 405 amino acids. This study was to identify the underlying genetic defects in a non-consanguineous Chinese family with Oguchi's disease.

Methods: Ophthalmologic examinations including fundus photography and electroretinography (ERG) were performed on all family members. All exons of the GRK1 gene and the SAG gene were amplified with PCR and directly sequenced. Quantitative real-time PCR (qPCR) was performed to screen heterozygous deletions/duplications in the SAG gene. Long-range PCR and direct sequencing were further performed to define the breakpoints.

Results: The patient had characteristic clinical features of Oguchi's disease, including night blindness, normal vision fields, typical fundus appearance with the Mizuo-Nakamura phenomenon, nearly undetectable rod b waves in the scotopic 0.01 ERGs, and nearly "negative" scotopic 3.0 ERGs. No mutations were found in the GRK1 gene. A heterozygous nonsense Arg193stop (R193X) mutation was found in the SAG gene in the patient and the unaffected mother. No pathogenic SAG mutations were found in the unaffected father. qPCRs showed a heterozygous deletion encompassing exon 2 of the SAG gene in the patient and the unaffected father. Long-range PCR and direct sequencing verified the deletion and revealed the breakpoints of the deletion, skipping a 3,224-bp fragment of the SAG gene. The deletion was not detected in 96 unrelated healthy controls. This deletion was predicted to eliminate the exon 2 and the AUG initiate codon in the mature SAG mRNA and cause no production of the SAG protein or low-level production of a non-functional truncated protein lacking 134 amino acids in the NH(2) terminus.

Conclusions: Compound heterozygosity of a nonsense R193X mutation and a heterozygous deletion of 3,224 bp encompassing exon 2 in the SAG gene is the cause of Oguchi's disease in this Chinese family. qPCR analysis should be performed if there is a negative result of the mutation screening of the SAG gene in patients with Oguchi's disease.

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Related in: MedlinePlus

Schematic representation of the mature mRNA of wild type and mutant type with exon 2 and the natural AUG codon eliminated. The in-frame coding regions are indicated in black box. The 5′ untranslated regions and out-frame coding regions are in clear box. The locations of in-frame AUG codons and out-of-frame AUG codons are indicated with triangles in black and in white, respectively. The numbers in the boxes depict the exons.
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f6: Schematic representation of the mature mRNA of wild type and mutant type with exon 2 and the natural AUG codon eliminated. The in-frame coding regions are indicated in black box. The 5′ untranslated regions and out-frame coding regions are in clear box. The locations of in-frame AUG codons and out-of-frame AUG codons are indicated with triangles in black and in white, respectively. The numbers in the boxes depict the exons.

Mentions: This deletion was predicted to eliminate the entire exon 2 of 103 nucleotides (nt) with the AUG initiation site in the mature mRNA of SAG and cause the use of downstream alternative AUG codons (Figure 6). The eukaryotic ribosomes are loaded on the 5′-cap of the mutant mRNA, scan for the translation initiation signal (TIS), and initiate the first AUG codon they encounter [22]. The first downstream AUG codon out of frame located in the exon 3 is recognized by the ribosome, initiating the translation of its open reading frame (ORF). A short peptide of 19 amino acids is produced, which is expected to stall ribosomes to its stop codon [23,24]. In addition, the premature termination codon leads to the rapid mRNA degradation by the pathway of the nonsense-mediated mRNA decay (NMD) [25]. If possible, the mRNAs if not all degraded may remain connected to the un-disassociated ribosomes stalled at the stop codon of the ORF, and thus, these ribosomes may resume scanning and reinitiate the next downstream TIS [26,27]. In this case, there would be three additional downstream out-of-frame AUG codons to be scanned by the ribosomes in the same way. And if the fifth in-frame AUG codon has a chance to be initiated, a predicted protein lacking 134 amino acids in the NH2 terminus would be expressed in a dramatically reduced level. Even if the expression level is high enough, the predicted truncated protein could be non-functional with impaired conformation of the NH2-terminal half of the SAG protein and disrupted interaction between the N domain and the C domain [28-31].


A Chinese family with Oguchi's disease due to compound heterozygosity including a novel deletion in the arrestin gene.

Huang L, Li W, Tang W, Zhu X, Ou-Yang P, Lu G - Mol. Vis. (2012)

Schematic representation of the mature mRNA of wild type and mutant type with exon 2 and the natural AUG codon eliminated. The in-frame coding regions are indicated in black box. The 5′ untranslated regions and out-frame coding regions are in clear box. The locations of in-frame AUG codons and out-of-frame AUG codons are indicated with triangles in black and in white, respectively. The numbers in the boxes depict the exons.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3298420&req=5

f6: Schematic representation of the mature mRNA of wild type and mutant type with exon 2 and the natural AUG codon eliminated. The in-frame coding regions are indicated in black box. The 5′ untranslated regions and out-frame coding regions are in clear box. The locations of in-frame AUG codons and out-of-frame AUG codons are indicated with triangles in black and in white, respectively. The numbers in the boxes depict the exons.
Mentions: This deletion was predicted to eliminate the entire exon 2 of 103 nucleotides (nt) with the AUG initiation site in the mature mRNA of SAG and cause the use of downstream alternative AUG codons (Figure 6). The eukaryotic ribosomes are loaded on the 5′-cap of the mutant mRNA, scan for the translation initiation signal (TIS), and initiate the first AUG codon they encounter [22]. The first downstream AUG codon out of frame located in the exon 3 is recognized by the ribosome, initiating the translation of its open reading frame (ORF). A short peptide of 19 amino acids is produced, which is expected to stall ribosomes to its stop codon [23,24]. In addition, the premature termination codon leads to the rapid mRNA degradation by the pathway of the nonsense-mediated mRNA decay (NMD) [25]. If possible, the mRNAs if not all degraded may remain connected to the un-disassociated ribosomes stalled at the stop codon of the ORF, and thus, these ribosomes may resume scanning and reinitiate the next downstream TIS [26,27]. In this case, there would be three additional downstream out-of-frame AUG codons to be scanned by the ribosomes in the same way. And if the fifth in-frame AUG codon has a chance to be initiated, a predicted protein lacking 134 amino acids in the NH2 terminus would be expressed in a dramatically reduced level. Even if the expression level is high enough, the predicted truncated protein could be non-functional with impaired conformation of the NH2-terminal half of the SAG protein and disrupted interaction between the N domain and the C domain [28-31].

Bottom Line: No mutations were found in the GRK1 gene.A heterozygous nonsense Arg193stop (R193X) mutation was found in the SAG gene in the patient and the unaffected mother.No pathogenic SAG mutations were found in the unaffected father. qPCRs showed a heterozygous deletion encompassing exon 2 of the SAG gene in the patient and the unaffected father.

View Article: PubMed Central - PubMed

Affiliation: Institute of Reproductive and Stem Cell Engineering, Central South University, Changsha, PR China.

ABSTRACT

Purpose: Oguchi's disease is a rare autosomal recessive disease and known to be caused by mutations in the rhodopsin kinase (GRK1) gene or the arrestin (SAG) gene. SAG contains 16 exons and encodes a protein with 405 amino acids. This study was to identify the underlying genetic defects in a non-consanguineous Chinese family with Oguchi's disease.

Methods: Ophthalmologic examinations including fundus photography and electroretinography (ERG) were performed on all family members. All exons of the GRK1 gene and the SAG gene were amplified with PCR and directly sequenced. Quantitative real-time PCR (qPCR) was performed to screen heterozygous deletions/duplications in the SAG gene. Long-range PCR and direct sequencing were further performed to define the breakpoints.

Results: The patient had characteristic clinical features of Oguchi's disease, including night blindness, normal vision fields, typical fundus appearance with the Mizuo-Nakamura phenomenon, nearly undetectable rod b waves in the scotopic 0.01 ERGs, and nearly "negative" scotopic 3.0 ERGs. No mutations were found in the GRK1 gene. A heterozygous nonsense Arg193stop (R193X) mutation was found in the SAG gene in the patient and the unaffected mother. No pathogenic SAG mutations were found in the unaffected father. qPCRs showed a heterozygous deletion encompassing exon 2 of the SAG gene in the patient and the unaffected father. Long-range PCR and direct sequencing verified the deletion and revealed the breakpoints of the deletion, skipping a 3,224-bp fragment of the SAG gene. The deletion was not detected in 96 unrelated healthy controls. This deletion was predicted to eliminate the exon 2 and the AUG initiate codon in the mature SAG mRNA and cause no production of the SAG protein or low-level production of a non-functional truncated protein lacking 134 amino acids in the NH(2) terminus.

Conclusions: Compound heterozygosity of a nonsense R193X mutation and a heterozygous deletion of 3,224 bp encompassing exon 2 in the SAG gene is the cause of Oguchi's disease in this Chinese family. qPCR analysis should be performed if there is a negative result of the mutation screening of the SAG gene in patients with Oguchi's disease.

Show MeSH
Related in: MedlinePlus