Analysis of Corneal Phenotypes in Japanese Patients With Myotonic Dystrophy Type 1

Purpose: To analyze the corneal phenotypes of Japanese patients with myotonic dystrophy type 1 (DM1).

Methods: We included patients with DM1 who were diagnosed with clinical neuromuscular symptoms by neurologists and CTG trinucleotide repeat (TNR) expansion of the (myotonic dystrophy protein kinase) DMPK gene. We analyzed the corneal phenotype using slit-lamp examination, specular microscopy, and anterior segment optical coherence tomography. We evaluated TNR expansion in the TCF4 gene of leukocyte-derived genomic DNA by fragment analysis using polymerase chain reaction and triplet-repeat primed polymerase chain reaction.

Results: Nineteen eyes from 10 patients with DM1 (DM1 group) and 72 eyes from 37 healthy participants (control group) were analyzed. The average age was 49.3 ± 11.9 and 51.8 ± 12.9 years in the DM1 and control groups, respectively (P = 0.11). Slit-lamp examination demonstrated that 2 patients with DM1 had bilateral corneal guttae equivalent to modified Krachmer grade 1 of Fuchs endothelial corneal dystrophy. Dark areas on specular microscopy were observed in 4 of 19 eyes (21.1%) and 0 of 72 eyes (0%) in the DM1 and control groups, respectively, with statistically significant differences (P = 0.002). The average endothelial cell density in the DM1 group (3536 ± 722 cells/mm2) was significantly higher than that in the control group (3026 ± 412 cells/mm2) (P = 0.0006). TNR expansion in TCF4 was not detected in eyes with corneal guttae or in the dark areas in the DM1 group.

Conclusions: Japanese patients with DM1 without TNR expansion in TCF4 have a mild phenotype equivalent to Fuchs endothelial corneal dystrophy. Endothelial cell density is higher in DM1 patients than in normal participants.