MONOZYGOTIC TWINS DISCORDANT FOR ASYMMETRIC PIGMENTED PARAVENOUS CHORIORETINAL ATROPHY

To demonstrate phenotypic discordance between a monozygotic twin pair, one of whom exhibited pigmented paravenous chorioretinal atrophy (PPCRA).

A patient and his identical twin brother, attending Moorfields Eye Hospital, were reviewed. Clinical assessment included visual acuity and color vision testing, fundus imaging including autofluorescence, spectral-domain optical coherence tomography, and static perimetry. In addition, the affected sibling underwent pattern and full-field electroretinography (PERG and ERG) according to ISCEV standards. Zygosity testing was performed using short tandem repeat analysis.

The 48-year-old proband was referred with abnormal visual fields and difficulty reading at near. Examination revealed 20/20 Snellen visual acuity bilaterally, normal color vision, and bilateral asymmetric outer retinal atrophy with intraretinal pigment migration along the course of the retinal veins, consistent with PPCRA. The visual field defects were contiguous with the blind spot and mirrored the retinal involvement in both eyes. Pattern ERG showed mild macular dysfunction and full-field ERG was within normal limits. Blood testing for common uveitic entities was noncontributory. The proband's twin brother's clinical assessment and retinal imaging showed no abnormality. Zygosity testing showed the twins to be identical for 24 short tandem repeat microsatellite markers, indicative of monozygosity.

Some cases of PPCRA, without an obvious inflammatory etiology, do not have a clear Mendelian inheritance pattern and may represent an acquired disorder.