Alu-element insertion in an OPA1 intron sequence associated with autosomal dominant optic atrophy

Abstract

Purpose: Autosomal dominant optic atrophy (ADOA) is the most common form of hereditary optic neuropathy caused by mutations in the optic atrophy 1 (OPA1) gene. It is characterized by insidious onset with a selective degeneration of retinal ganglion cells, variable loss of visual acuity, temporal optic nerve pallor, tritanopia, and development of central, paracentral, or cecocentral scotomas. Here we describe the clinical and molecular findings in a large Italian family with ADOA.

Methods: Routine ophthalmologic examination and direct sequencing of all coding regions of the OPA1 gene were performed. Further characterization of a new OPA1 gene insertion was performed by reverse transcription-PCR (RT-PCR) of RNA from patients and control subjects.

Results: We identified an Alu-element insertion located in intron 7 of OPA1 causing an in-frame deletion of exon 8 in 18 family members.

Conclusions: The predicted consequence of this mutation is the loss of the guanosine triphosphatase (GTPase) activity of OPA1. Alu insertions have been reported in the literature as causing human genetic disease. However, this is the first report of a pathogenic OPA1 gene mutation resulting from an Alu insertion.

Figure 1

Pedigree diagram of the Autosomal Dominant Optic Atrophy (ADOA) family. The pedigree of a five-generation family shows eighteen affected members. Solid squares mean male patients, open circles mean normal females, solid circles mean female patients, open squares mean normal males, arrow means proband (V-3). Oblique lines through circles and squares represent deceased, vertical lines indicate the presence of the mutation in two unaffected family members (IV-7 and IV-10) and in another family member not available for ophthalmological examination (V-15).

Figure 2

OPA1 mutation in the Autosomal Dominant Optic Atrophy (ADOA) family. A shows the agarose gel of products from polymerase chain reaction (PCR) of exon 8. Lane 1 is patient sample (V-3), lanes 2 and 3 are normal controls, lane 4 is patient’s mother (IV-8). B shows comparison of sequences of allele with Alu insertion and normal allele. Exon sequence is shown in bold and highlighted in sky blue; direct repeats flanking the Alu insertion are shown in bold and underlined; Alu element with poly(A) tail is highlighted in yellow; arrows in the normal sequence indicate the cuts. C shows complementary and reverse sequence of mutated region in OPA1 gene with sequence elements of the Alu repeat. Consensus target site is shown in red bold characters and underlined; target-site duplications of the OPA1 gene sequence flanking the integrated DNA are highlighted in sky blue; A and B box sequences (RNA polymerase III promoter) are highlighted in green and violet, respectively; poly(A) tail is highlighted in yellow. D shows the agarose gel of products from reverse transcription–PCR of exons 6–10 of the OPA1 gene. Lane 1 is patient sample (V-3), lanes 2, 3, and 4 are normal controls. E shows electropherogram section with the skipping of exon 8.