A hospital-based five-year prospective study on the prevalence of Leber's hereditary optic neuropathy with genetic confirmation

Abstract

Purpose: To estimate the prevalence of Leber hereditary optic neuropathy (LHON) along with genetic screening at a tertiary eye care center in southern India.

Methods: Patients with LHON were identified at the Neuro-Ophthalmology Clinic, Aravind Eye Hospital (AEH; Madurai, India) from 2015 to 2019. Clinical data were collected along with blood samples. Genetic testing was performed for the confirmation of LHON using a multiplex PCR restriction fragment length polymorphism (RFLP) approach to detect the primary mutations 3460A, 11778A, and 14484C in mitochondrial DNA (mtDNA).

Results: During the study period, 1,598,441 outpatients attended AEH of whom 40,527 were referred to the Neuro-Ophthalmology Clinic. Among them, 55 patients were diagnosed with LHON. The male to female ratio was 8.2:1.0, and the mean age at onset was 20.95 years (SD 8.940). The estimated prevalence was 1:737 or 13.57 per 10,000 (95% confidence intervals [CI] 10.23-17.66) at the Neuro-Ophthalmology Clinic. The frequency of primary mutations in the patients with LHON was determined as 43.6% (24/55), giving a prevalence of 1:1689 or 5.92 per 10,000 (95% CI 3.78-8.81).

Conclusions: The high prevalence of LHON observed at a single hospital highlights the impact of the disease in southern India. As the epidemiology of LHON remains unexplored in this region, these findings will pave the way to evaluate the national prevalence. Further, screening the whole mitochondrial genome may help to increase the detection of mutations to estimate the accurate prevalence of the disease.

Figure 1

Fundus and OCT examination of patient with LHON. A: Evaluation of the fundus shows swelling of the retinal nerve fiber layer (RNFL) in both eyes, hyperemic disc in the right eye (OD), and diffuse disc pallor in the left eye (OS). B: Optical coherence tomography (OCT) examination displays loss of the ganglion cell layer.

Figure 2

Age at onset of 55 patients with newly developed LHON during 2015–2019. Disease onset was found to be relatively lower in the case of women than in men. A rare case of late onset Leber hereditary optic neuropathy (LHON) was observed in a 56-year-old man.

Figure 3

Human mitochondrial genome and detection of primary mutations in LHON samples. A: Schematic representation of the human mtDNA map indicating 37 genes including MT-ND1, MT-ND4 and MT-ND6 as well as the positions of primary mutations. Figure adapted from chimerasthebooks. B: The red arrow demonstrates the internal control of digestion in the MT-ND1 gene product. The yellow arrows indicate the MaeIII restriction, detecting the corresponding mutations marked in blue arrows.

Figure 4

Sanger sequencing validation of restriction fragment length polymorphism. Chromatograms showing the presence of G11778A (left-A) and T14484C (right-B) mtDNA mutations in the same samples confirm the restriction fragment length polymorphism (RFLP) findings.