[A Study of Clinical and Genetic Characteristics of a Leber Hereditary Optic Neuropathy Family with the Heteroplasmic M.14484t>c Mutation].

Objective: To study clinical and genetic characteristics of a Leber hereditary optic neuropathy (LHON) family with the heteroplasmic m.14484T>C mutation. Methods: A cross-sectional study. The objects of the study included a 31-year-old male LHON patient with the heteroplasmic m.14484T>C mutation (the proband) who visited Department of Ophthalmology in the Affiliated Central Hospital of Qingdao University in March 2015 and other 36 matrilineal relatives in a four-generation family (12 males and 24 females aged 2-81 years, median 27 years). The visual acuity, intraocular pressure, fundus, color vision, visual field, visual evoked potential and optical coherence tomography were evaluated in maternal members. The mitochondrial DNA (mtDNA) sequence of fragments including m.14484 loci was detected by Sanger sequencing in 33 members. The sequencing peaks were analyzed by QSVanalyzer software to get the heteroplasmy levels of m.14484T>C mutation. The mtDNA of the proband was amplified by PCR and sequenced. Assembled sequence of mtDNA was compared with the updated consensus Cambridge sequence. The differences in visual evoked potential, optical coherence tomography and heteroplasmy levels were compared between two groups by the t-test, and among multiple groups by the single factor variance analysis. Results: Among the 33 maternal members of the family, 4 patients, 28 carriers and 1 person without a mutation were confirmed. The penetrance was 12.5% (4/32) . In addition to 4 patients with obvious abnormality on the ophthalmic examination, 5 carriers also appeared anomaly on the electrophysiological and visual function examinations. Compared to carriers, the amplitude of P100 was obviously decreased in the LHON patients[ (5.6±2.6) μV vs. (15.6±9.6) μV, t=2.880, P=0.006]. Significantly reduced values were seen in the average retinal nerve fiber layer thickness[ (71±17) μm vs. (99±11) μm, t=5.969, P< 0.001], in each side of the sub-area macular thickness, and in the nasal side of the lateral sub-area macular thickness [ (260±16) μm vs. (291±12) μm, t=5.593, P<0.001] between the LHON patients and carriers. The heteroplasmic levels were 80%±3% in the LHON patients, and 27%±18% in the unaffected members;the difference was significant (t=-8.395, P<0.001). The average degree of heteroplasmy had no difference between male and female members (48%±34% vs. 35%±28%, t=-1.147, P=0.258). The average mutation load was 29%±14% in the second generation members, 36%±29% in the third generation members, and 51%±36% in the fourth generation members;the differences were not statistically significant (F=1.152, P=0.330). The difference in the heteroplasmic levels was not statistically significant between mothers and their offspring (31%±25% vs. 42%±32%, t=1.165, P=0.251). Compared to Cambridge consensus sequence, 41 mutations was found in mtDNA of the proband, of which, 10 were missense mutations, including mutations m.4216T>C and m.3394T>C. According to the phylogenetic tree, the haplotype of the proband was M9a (M9a1a1c1a). Conclusions: In the family with the heteroplasmic m.14484T>C mutation, clinical manifestations of LHON appear in the individuals whose heteroplasmic level is more than 75%, and all of patients show typical chronic optic atrophy on the ophthalmic examination. The carriers with the m.14484T>C mutation also appear anomaly on the electrophysiological and visual function examinations. The heteroplasmic level of m.14484T>C mutation has a tendency to increase during the transmission in the family. The primary mutation m.14484T>C coordinate mutations m.4216T>C and m.3394T>C to increase the penetrance and incidence of abnormal visual function in carriers. (Chin J Ophthalmol, 2018, 54: 526-534).