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Novel ABCA4 compound heterozygous mutations cause severe progressive autosomal recessive cone-rod dystrophy presenting as Stargardt disease.

Xi Q, Li L, Traboulsi EI, Wang QK - Mol. Vis. (2009)

Bottom Line: Unaffected family members either did not carry either or had only one of the two mutations.We have identified two novel ABCA4 mutations, c.655A>T and c.5312+3A>T.These results expand the wide range of clinical manifestations of ABCA4 mutations.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Cardiology, Center for Cardiovascular Genetics, Lerner Research Institute, The Cleveland Clinic, Cleveland, OH, USA.

ABSTRACT

Purpose: To identify the gene causing a severe form of progressive autosomal recessive cone-rod dystrophy presenting as Stargardt disease and to characterize clinical features in a large American family.

Methods: We characterized an American family who had an unusual retinal dystrophy with clinical features of Stargardt disease and severe progressive cone-rod dystrophy. Family members underwent complete ocular examinations with evaluation of visual acuity, visual fields, fundus examination, fluorescein angiography, and electroretinography. Genome-wide linkage analysis of the family was performed using 408 microsatellite markers spanning the entire human genome. Direct DNA sequence analysis was used for mutational analysis of the ABCA4 gene in all exons and exon-intron boundary regions and for testing cosegregation of the mutations with the disease in the family. DNA sequence analysis was used to determine the presence of the mutations in 200 unrelated controls.

Results: The proband presented with a clinical phenotype that was initially compatible with Stargardt disease, only to progress to a severe cone-rod dystrophy over the course of a few years. The disease-causing gene in the family was linked to the ABCA4 locus on chromosomal 1p22. One novel mutation, c.655A>T, was identified in exon 6 and another novel splicing mutation, c.5312+3A>T, was identified in intron 37 of ABCA4. The mutations were not present in 200 controls. The two affected sisters in this pedigree were compound heterozygotes for the mutations. Unaffected family members either did not carry either or had only one of the two mutations.

Conclusions: We have identified two novel ABCA4 mutations, c.655A>T and c.5312+3A>T. When present as a compound heterozygous state, the mutations cause a phenotype of retinal dystrophy that initially manifests as Stargardt disease and slowly progresses to a severe cone-rod dystrophy. These results expand the wide range of clinical manifestations of ABCA4 mutations.

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Related in: MedlinePlus

Identification of two novel ABCA4 mutations. DNA sequence analysis for patient II-1 showed the presence of compound heterozygous c.655A>T and c.5312+3A>T mutations. A and D show the sequences from a normal and affected family member with mutation c.655A>T allele, respectively. B and E show the sequences from a normal and affected family member with mutation c.5312+3A>T allele, respectively. C and F show sequences for the wild type and mutant c.5312+3A>T allele, respectively, which were separated by subcloning of PCR products from an affected family member.
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f3: Identification of two novel ABCA4 mutations. DNA sequence analysis for patient II-1 showed the presence of compound heterozygous c.655A>T and c.5312+3A>T mutations. A and D show the sequences from a normal and affected family member with mutation c.655A>T allele, respectively. B and E show the sequences from a normal and affected family member with mutation c.5312+3A>T allele, respectively. C and F show sequences for the wild type and mutant c.5312+3A>T allele, respectively, which were separated by subcloning of PCR products from an affected family member.

Mentions: The ABCA4 gene (position, 94,239,702–94,249,073 bp) is located within the locus and became a strong candidate gene responsible for the phenotype in the family. PCR primers were designed to amplify and sequence all exons and exon-intron boundaries of the ABCA4 gene. Two novel mutations were identified (Figure 3). An A to T change in exon 6 (c.655A>T) resulted in a stop codon and thus generated a mutant ABCR protein (p.R219X; Figure 3A for wild type and Figure 3D for mutant sequence). The other mutation of A to T change (c.5312+3A>T) was identified at a 5′ splicing site in intron 37 (Figure 3B for wild type and Figure 3E for mutant sequence). For confirmation of the splicing mutation, PCR products were cloned and multiple clones were sequenced. Mutation c.5312+3A>T was confirmed (Figure 3C showing wild type and Figure 3F showing mutant, both from cloned PCR products). The substitution of A with T will abolish the splicing site as demonstrated by analysis with NetGene2. The mutation was predicted to introduce intron 37 into the mature ABCA4 mRNA during post-transcriptional splicing and cause a frameshift. The predicted mutant protein would have 1–1770 amino acid residues of ABCR followed by seven exogenous amino acid residues (LAVWAIS) that are translated from the sequence of intron 37. Amino acid residues 1771–2273 of ABCR would be deleted in the mutant protein.


Novel ABCA4 compound heterozygous mutations cause severe progressive autosomal recessive cone-rod dystrophy presenting as Stargardt disease.

Xi Q, Li L, Traboulsi EI, Wang QK - Mol. Vis. (2009)

Identification of two novel ABCA4 mutations. DNA sequence analysis for patient II-1 showed the presence of compound heterozygous c.655A>T and c.5312+3A>T mutations. A and D show the sequences from a normal and affected family member with mutation c.655A>T allele, respectively. B and E show the sequences from a normal and affected family member with mutation c.5312+3A>T allele, respectively. C and F show sequences for the wild type and mutant c.5312+3A>T allele, respectively, which were separated by subcloning of PCR products from an affected family member.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2665199&req=5

f3: Identification of two novel ABCA4 mutations. DNA sequence analysis for patient II-1 showed the presence of compound heterozygous c.655A>T and c.5312+3A>T mutations. A and D show the sequences from a normal and affected family member with mutation c.655A>T allele, respectively. B and E show the sequences from a normal and affected family member with mutation c.5312+3A>T allele, respectively. C and F show sequences for the wild type and mutant c.5312+3A>T allele, respectively, which were separated by subcloning of PCR products from an affected family member.
Mentions: The ABCA4 gene (position, 94,239,702–94,249,073 bp) is located within the locus and became a strong candidate gene responsible for the phenotype in the family. PCR primers were designed to amplify and sequence all exons and exon-intron boundaries of the ABCA4 gene. Two novel mutations were identified (Figure 3). An A to T change in exon 6 (c.655A>T) resulted in a stop codon and thus generated a mutant ABCR protein (p.R219X; Figure 3A for wild type and Figure 3D for mutant sequence). The other mutation of A to T change (c.5312+3A>T) was identified at a 5′ splicing site in intron 37 (Figure 3B for wild type and Figure 3E for mutant sequence). For confirmation of the splicing mutation, PCR products were cloned and multiple clones were sequenced. Mutation c.5312+3A>T was confirmed (Figure 3C showing wild type and Figure 3F showing mutant, both from cloned PCR products). The substitution of A with T will abolish the splicing site as demonstrated by analysis with NetGene2. The mutation was predicted to introduce intron 37 into the mature ABCA4 mRNA during post-transcriptional splicing and cause a frameshift. The predicted mutant protein would have 1–1770 amino acid residues of ABCR followed by seven exogenous amino acid residues (LAVWAIS) that are translated from the sequence of intron 37. Amino acid residues 1771–2273 of ABCR would be deleted in the mutant protein.

Bottom Line: Unaffected family members either did not carry either or had only one of the two mutations.We have identified two novel ABCA4 mutations, c.655A>T and c.5312+3A>T.These results expand the wide range of clinical manifestations of ABCA4 mutations.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Cardiology, Center for Cardiovascular Genetics, Lerner Research Institute, The Cleveland Clinic, Cleveland, OH, USA.

ABSTRACT

Purpose: To identify the gene causing a severe form of progressive autosomal recessive cone-rod dystrophy presenting as Stargardt disease and to characterize clinical features in a large American family.

Methods: We characterized an American family who had an unusual retinal dystrophy with clinical features of Stargardt disease and severe progressive cone-rod dystrophy. Family members underwent complete ocular examinations with evaluation of visual acuity, visual fields, fundus examination, fluorescein angiography, and electroretinography. Genome-wide linkage analysis of the family was performed using 408 microsatellite markers spanning the entire human genome. Direct DNA sequence analysis was used for mutational analysis of the ABCA4 gene in all exons and exon-intron boundary regions and for testing cosegregation of the mutations with the disease in the family. DNA sequence analysis was used to determine the presence of the mutations in 200 unrelated controls.

Results: The proband presented with a clinical phenotype that was initially compatible with Stargardt disease, only to progress to a severe cone-rod dystrophy over the course of a few years. The disease-causing gene in the family was linked to the ABCA4 locus on chromosomal 1p22. One novel mutation, c.655A>T, was identified in exon 6 and another novel splicing mutation, c.5312+3A>T, was identified in intron 37 of ABCA4. The mutations were not present in 200 controls. The two affected sisters in this pedigree were compound heterozygotes for the mutations. Unaffected family members either did not carry either or had only one of the two mutations.

Conclusions: We have identified two novel ABCA4 mutations, c.655A>T and c.5312+3A>T. When present as a compound heterozygous state, the mutations cause a phenotype of retinal dystrophy that initially manifests as Stargardt disease and slowly progresses to a severe cone-rod dystrophy. These results expand the wide range of clinical manifestations of ABCA4 mutations.

Show MeSH
Related in: MedlinePlus