BMJ Open Ophth: first published as 10.1136/bmjophth-2018-000180 on 17 November 2018. Downloaded from Original articles Ophthalmic phenotype of TCIRG1 gene mutations in Chinese infantile malignant osteopetrosis Wenhong Cao,1,2 Wenbin Wei,2 Qian Wu1 To cite: Cao W, Wei W, Wu Q. ABSTRACT Key messages Ophthalmic phenotype of Objective To evaluate the ophthalmic phenotypes TCIRG1 gene mutations associated with T-cell immune regulator 1 (TCIRG1) What is already known about this subject? in Chinese infantile mutations in Chinese patients with infantile malignant malignant osteopetrosis. T-cell immune regulator 1 (TCIRG1) is one of the osteopetrosis (IMO). ► BMJ Open Ophthalmology main genes that are responsible for the majority of Methods and analysis 27 Chinese TCIRG1-related 2018;3:e000180. doi:10.1136/ infantile malignant osteopetrosis (IMO) cases, which osteoporosis infants were enrolled using direct DNA bmjophth-2018-000180 are characterised by neonatal and infantile onset, a sequencing of PCR-amplified exons. 12 cases had systemic sclerosis of bones, vulnerability to fracture, frameshift mutation (the frameshift mutation group, group progressive anaemia, infection, hepatosplenomega- Received 30 May 2018 F), and 15 cases had point mutation (the point mutation ly and cranial nerve dysfunction, including poor gaze Revised 25 September 2018 group, group P). The clinical features of the two groups qualities, optic atrophy and optic canal stenosis. Accepted 26 September 2018 were compared, including age at onset, gaze qualities, To our knowledge, there is no study on the ophthal- optic atrophy, optic canal stenosis and waveforms of Flash ► mic phenotypes of TCIRG1 mutations in patients visual-evoked potential (FVEP). with IMO. Results The clinical signs, except age at onset and FVEP, showed statistically significant differences between the What are the new findings? two groups. The mean age at onset was 1.8 months in ► We found that by comparing frameshift and point group F and 4.3 months in group P; 22 eyes (92%) with mutation cases in 27 Chinese patients with TCIRG1- frameshift mutation and 16 (53%) with point mutation had IMO, severity of the ocular manifestations was relat- poor gaze qualities, such as nystagmus and/or strabismus; ed to the type of gene mutation, and the frameshift optic atrophy was found in 16 eyes (67%) in group F and mutation in TCIRG1 led to more serious phenotypes. 6 (20%) in group P; the average optic canal diameter was 1.45 mm in the frameshift mutation cases, 1.87 mm in How might these results change the focus of other cases; FVEP indicated that the waveforms in 10 eyes research or clinical practice? (42%) were not elicited in group F, yet five eyes (17%) in ► Future studies should assess the correlation of group P. TCIRG1 gene mutation and the mechanism of ocular http://bmjophth.bmj.com/ Conclusion In Chinese TCIRG1-related patients of IMO, sign occurrence. the optic canal stenosis and optic atrophy were more ► This may encourage better understanding of the © Author(s) (or their serious in cases with frameshift mutations. However, no mechanism of ocular sign occurrence and more tar- employer(s)) 2018. Re-use differences in the conduction block of optic nerve were geted treatment of IMO. permitted under CC BY-NC. No found between the two groups. commercial re-use. See rights and permissions. Published by 2 BMJ. and severity contribute to a high mortality. 1 Department of Ophthalmology, INTRODUCTION It is inherited as an autosomal recessive trait, on October 2, 2021 by guest. Protected copyright. Beijing Children’s Hospital, To date, more than 10 osteopetrosis-causing with an incidence of 1 in 250 000 births in National Center for Children’s genes have been identified.1 The inheri- North America, particularly high incidence Health, National Key Discipline tance patterns include autosomal dominant, reported in Costa Rica (3.4:100 000).3 of Pediatrics, Capital Medical autosomal intermediate, autosomal reces- Currently, T-cell immune regulator 1 University, Beijing, China 4 2Beijing Tongren Eye Center, sive and X linked. The disease severity also (TCIRG1, Gene ID: 10312, MIM 604592) is Beijing Key Laboratory of varies from malignant, intermediate, to mild one of the main genes that are responsible for Ophthalmology and Visual manifestations. Infantile malignant osteope- more than 50% of IMO cases.5 6 It has been Science, Beijing Key Laboratory trosis (IMO) is an extremely rare congenital reported that homozygous mutations in the of Intraocular Tumor Diagnosis disease caused by bone marrow failure genes encoding the a3 subunit of VATPase and Treatment, Beijing Tongren Hospital, Capital Medical resulting from osteoclast dysfunction. This (TCIRG1) produce severe malignant osteo- University, Beijing, China disorder is characterised by neonatal and petrosis phenotypes in both humans and infantile onset, a systemic sclerosis of bones, mice.4 Mutations in TCIRG1 associated with Correspondence to vulnerability to fracture, progressive anaemia, general clinical features have been reported 7 8 Dr Wenbin Wei; weiwenbintr@ infection, hepatosplenomegaly and cranial in previous studies. In this study, we present 163. com nerve dysfunction. The rapid progression a more detailed investigation of the relation Cao W, et al. BMJ Open Ophth 2018;3:e000180. doi:10.1136/bmjophth-2018-000180 1 BMJ Open Ophth: first published as 10.1136/bmjophth-2018-000180 on 17 November 2018. Downloaded from Open access between the ophthalmic phenotype of Chinese patients than 2 mm. The optic canal diameter was measured inde- with IMO and the genotype of TCIRG1 mutation. pendently by two radiologists and reviewed by the third radiologist. Children were in the supine position with a SUBJECTS AND METHODS cushion under their heads. Axial scanning was used, and The study was conducted in accordance with the Declara- the reconstruction was multiplanar reconstruction. The tion of Helsinki with approval from the Ethics Committee scanning parameters were as follows: tube volt 80 kV; of Beijing Children’s Hospital. Written informed consent pitch 1.375; depth 1 mm; interlamellar spacing 1 mm; was obtained from all the parents of each child as well as and a 256×256 matrix. The average radiation dose in their own participation in the study. this study was 1.09±0.02 mGy, which is much lower than the American College of Radiology CT accredited CT TCIRG1 gene mutation analysis Dosimetry Index reference level of 75 mGy. A low-dose Blood samples were collected from patients (families) CT protocol for children was followed for the purpose of with IMO at Beijing Children’s Hospital, Capital Medical this study. University. Twenty-seven patients with TCIRG1-related FVEP was examined using a visual electrophysiology osteopetrosis were included in the study by gene detec- system (Roland, Germany). The standard FVEP protocol tion. We performed mutation analysis of the TCIRG1 recommended by the International Standard EEG 10–20 gene using direct DNA sequencing of PCR-amplified System (International Society for Clinical Electrophys- exons (the mutation nomenclature conforms to www. iology of Vision) was followed: the examination was hgvs.org/ mutnomen). The TCIRG1 gene was amplified performed in a darkroom; the electrodes including the from genomic DNA (genomic sequence AF033033) in active electrode, reference electrode and ground elec- the conditions previously described.6 Prediction of the trode were placed; the eyes were stimulated by a mini protein domains was based on the potential topological handheld stimulator separately and repeated twice per domains reported in UniProt database (Q13488; www. eye, with more than 70 superposition times. The exci- uniprot. org) and refined by homology with the yeast tation frequency was set at 30 Hz. subunit a (Vph1p).9 The putative structural consequences of mutations were estimated in silico by sequence analysis Statistical analysis and multiple sequence alignment information. Patients Statistical analyses were performed using SPSS V.13.0. with other gene-related osteopetrosis were excluded. In two groups, gaze qualities, optic atrophy and FVEP 2 None of these Chinese probands were the offspring of a waveform were respectively compared by Pearson χ , age consanguineous marriage. Of the 27 patients with IMO, at onset by Mann-Whitney U test and optic canal diam- 12 had a frameshift mutation (the frameshift mutation eter by Student’s t-test. Alpha correct p values for five group, group F) while 15 had a point mutation (the point comparisons (0.05/5=0.01) were considered as statisti- mutation group, group P). cally significant. Clinical examination RESULTS http://bmjophth.bmj.com/ A clinical diagnosis of osteopetrosis was made on the All cases in group F and group P had ocular symptoms basis of the following criteria at presentation (which has and signs of IMO such as loss of vision, optic canal been described by the previous study10 11 : early symptom stenosis, with/without nystagmus, strabismus, or optic onset (before 2 years of age), high bone mineral density, atrophy. The clinical and genetic data of the 27 patients bone marrow failure with consequent pancytopenia, with TCIRG1 mutations were summarised in table 1. hepatosplenomegaly and cranial nerve palsies by the The male:female ratio was 7:5 in the frameshift muta- haematology specialists. The ophthalmological features tion group and 9:6 in the point mutation group. The at the onset of IMO were ascertained in all 27 cases by mean age at onset was 1.8 months in group F and 4.3 on October 2, 2021 by guest. Protected copyright. examining the clinical records at Beijing Children’s months in group P, but there was no significant differ- Hospital. We compared the group F with the group P in ence in these two groups (table 2; Mann-Whitney U test, terms of sex, age at diagnosis of IMO and appearance of p=0.028<0.05). eye (eg, gaze properties including nystagmus, strabismus, Significant differences in the clinical findings were optic atrophy, optic canal diameter and waveform of found between the two groups (table 2).