Sir,

Mytonic dystrophy type 1 (DM1) is an autosomal dominant disorder caused by mutation in the dystrophia myotonica protein kinase (DMPK) gene, located on chromosome 19 (19q13.2–q13.3). Ocular findings reported to date include colored iridescent cataract, strabismus, and limitation of extraocular muscle movement, ptosis, and rarely macular dystrophy.1

Case report

A 21-year-old male with DM1 presented with a 4-week history of deteriorating vision in his left eye, assumed to be cataract. Clinical examination, however, showed bilateral pattern dystrophy (Figure 1a) with best corrected visual acuity (VA) recorded at 6/6 in the right eye and 6/15 in the left eye, which had choroidal new vessels (CNVs) (Figures 1b and 2aI). Treatment followed consent of the off-label nature of intravitreal bevacizumab (IVB). After 4 weeks, symptoms had improved but due to persisting intraretinal fluid (Figure 2aII) a second IVB injection was given. After 4 weeks, VA had improved to 6/7.5 with both OCT and angiography confirming no leakage (Figures 2aIII and b). No recurrence was seen at most recent follow-up 14 months later. His father who had DM1 was also examined, but did not have macular dystrophy.

Figure 1
figure 1

(a) Color images of right and left fundus with pattern retinal pigment epithelium changes. Subretinal hemorrhages are evident in the center of the left macula. (b) Late fundus fluorescein angiogram images before treatment shows RPE changes and, in the left eye, central leakage.

Full size image
Figure 2
figure 2

(a) OCT images of the left eye. (I) Left OCT shows central retinal edema, subretinal fluid, loss of foveal contour, and intense sub-RPE hyperreflectivity pigment suggesting occult CNV at initial presentation (I), 4 weeks after the first IVB (II) and 4 weeks after the second IVB injection (III). (b) Late-phase fluorescein angiography confirms complete resolution of central leakage in the left eye.

Full size image

Comment

To our knowledge this is the first report of CNVs complicating DM1. The cause of the macular phenotype is still unknown. The expansion of CTG triplet repeats in DM1 arise within the 3’ untranslated region of the DMPK gene,2, 3 but this region also overlaps downstream with the promoter of the homeobox gene SIX5 on chromosome 19q13.3.4 As expression of this gene has been localized to the lens, retina, and choroid, it has been proposed that SIX5 and not DMPK is responsible for the ocular phenotype of DM.5 The non-penetrant inheritance of the macular dystrophy, might either indicate a digenic pattern where transcriptional silencing of the SIX5 gene through expansion of CTG repeats occurs from one generation to the next through anticipation or it might indicate variable expressivity. Beyond the genetics, our observations show that deterioration of VA in patients with DM can be due to macular dystrophy and, rarely, CNVs. The rapid response to IVB provides evidence that VEGF has a role in this disease.