Yanhua Qi

Autosomal-Dominant Cerulean Cataract in a Chinese Family Associated with Gene Conversion Mutation in Beta-B2-Crystallin

Aims: Our purpose was to identify the genetic defect in a Chinese cerulean cataract family. Methods: After obtaining informed consent, genomic DNA was extracted from leukocytes. Genotyping and 2-point linkage analysis were carried out using the MLINK component of the LINKAGE program package version 5.10. Mutational analysis of the candidate gene was performed by bidirectional sequencing. The structure homology modeling of the mutant protein was based on Swiss-Model Serve, and its structure was displayed and compared with native β-B2-crystallin using the RasMol software. Results: The disease locus was mapped within a 4.05-cM interval on 22q11.22–22q12.1. By sequencing, a cytosine to thymine transition (NM_000496.2:c.463C>T) was detected in exon 6 of CRYBB2, which resulted in the insertion of a premature stop codon (p.Q155X). In addition, there existed another transition (NM_000496.2:c.471C>T) in the same exon, which does not change the amino acid sequence. Neither NM_000496.2:c.463C>T nor NM_000496.2:c.471C>T were found in 171 normal Chinese controls. The homology modeling showed that the second structure of the mutant protein was different from that of native human β-B2-crystallin. Conclusions: This is the first report of congenital cerulean cataract associated with a mutation in CRYBB2 in a Chinese family. This finding further strengthens the association between CRYBB2 and cerulean cataracts. Two transitions, NM_000496.2:c.463C>T and NM_000496.2:c.471C>T, in CRYBB2 are identical to the sequence of CRYBB2P1, which has over 97% homology to CRYBB2. This supports the possibility of gene conversion between CRYBB2 and CRYBB2P1 as a mechanism responsible for congenital cataract.

Mutational Screening of EFNA5 in Chinese Age-Related Cataract Patients

Background/Aim: In the past few years, Ephrin-A5 (EFNA5) had been identified to be associated with lens development, but so far no sequence variation in EFNA5 has been reported in humans. Therefore, we conduct this study to investigate the EFNA5 genetic variations in Chinese age-related cataract (ARC) patients. Methods: Sequencing of EFNA5 was performed in 140 sporadic ARC patients and 142 random unrelated healthy subjects. Genomic DNA was extracted from peripheral blood leukocytes. All exons of EFNA5 were sequenced after being amplified by polymerase chain reaction. The functional consequences of the variations were analyzed using PolyPhen2. Results: Three single nucleotide polymorphisms in EFNA5, c.668C>T (rs201008479), c.102C>T (rs199980747) and c.-27C>G (rs200187971), were found in the patients, and none of them presented in the normal controls. Using PolyPhen2, c.668C>T in EFNA5 is predicted to be possibly damaging. Conclusions: The genetic variations c.668C>T (rs201008479), c.102C>T (rs199980747) and c.-27C>G (rs200187971) may present an additional genetic risk factor for ARC in the Chinese population. This study shows the first cases of these genetic variations in EFNA5 in human beings.

Threshold Suprachoroidal-Transretinal Stimulation Current Required by Different-Size Electrodes in Rabbit Eyes

Aims: To evaluate the threshold currents required by different-size electrodes under various stimulus parameters by suprachoroidal-transretinal stimulation (STS) in rabbit eyes. Methods: An electrode array with 4 differently sized electrode contacts (50, 150, 350 and 500 µm in diameter) was implanted into the suprachoroidal space of the rabbit eyes. The electrically evoked potential was recorded extradurally on the visual cortex, and the threshold was measured for each size electrode by a biphasic current pulse at the pulse durations of 0.25, 0.5, 0.75 and 1.0 ms. Stimuli were applied at 1, 2 and 4 Hz. Results: The current thresholds with the 50-µm electrode were 80 ± 21.2 and 41.4 ± 6.5 µA for 0.25- and 1.0-ms pulses, respectively. That obviously exceeded the limits for safe stimulation with platinum. Compared to 350- and 500-µm electrodes, a lower threshold can be obtained by the 150-µm electrode just at 1 Hz. And the most significant change in the threshold as the stimulus frequency increased to 4 Hz was obtained by the 150-µm electrode with short-duration pulse (0.25 ms). Conclusion: The large surface electrode with long-duration pulses may be preferable for the STS prosthesis. And stimuli with low frequency are suggested to be the safer choice.