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   Table of Contents      
ORIGINAL ARTICLE
Year : 2016  |  Volume : 64  |  Issue : 11  |  Page : 813-817

A previously unidentified deletion in G protein-coupled receptor 143 causing X-linked congenital nystagmus in a Chinese family


1 Department of Ophthalmology, Peking University Third Hospital, Key Laboratory of Vision Loss and Restoration, Ministry of Education, Beijing 100191, P. R. China
2 Department of ophthalmology, The Municipal Hospital of Zaozhuang, Shandong 277100, P. R. China

Date of Submission08-May-2016
Date of Acceptance16-Oct-2016
Date of Web Publication13-Dec-2016

Correspondence Address:
Juan Bu
Department of Ophthalmology, Peking University Third Hospital, Key Laboratory of Vision Loss and Restoration, Ministry of Education, Beijing 100191
P. R. China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0301-4738.195593

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  Abstract 

Background: Congenital nystagmus (CN) is characterized by conjugated, spontaneous, and involuntary ocular oscillations. It is an inherited disease and the most common inheritance pattern is X-linked CN. In this study, our aim is to identify the disease-causing mutation in a large sixth-generation Chinese family with X-linked CN. Methods: It has been reported that mutations in four-point-one, ezrin, radixin, moesin domain-containing 7 gene (FRMD7) and G protein-coupled receptor 143 gene (GPR143) account for the majority patients of X-linked nystagmus. We collected 8 ml blood samples from members of a large sixth-generation pedigree with X-linked CN and 100 normal controls. FRMD7 and GPR143 were scanned by polymerase chain reaction (PCR)-based DNA sequencing assays, and multiplex PCR assays were applied to detect deletions. Results: We identified a previously unreported deletion covering 7 exons in GPR143 in a Chinese family. The heterozygous deletion from exon 3 to exon 9 of GPR143 was detected in all affected males in the family, while it was not detected in other unaffected relatives or 100 normal controls. Conclusions: This is the first report of molecular characterization in GPR143 gene in the CN family. Our results expand the spectrum of GPR143 mutations causing CN and further confirm the role of GPR143 in the pathogenesis of CN.

Keywords: Four-point-one, ezrin, radixin, moesin domain-containing 7 gene, G protein-coupled receptor 143 gene, X-linked congenital nystagmus


How to cite this article:
Liu J, Jia Y, Wang L, Bu J. A previously unidentified deletion in G protein-coupled receptor 143 causing X-linked congenital nystagmus in a Chinese family. Indian J Ophthalmol 2016;64:813-7

How to cite this URL:
Liu J, Jia Y, Wang L, Bu J. A previously unidentified deletion in G protein-coupled receptor 143 causing X-linked congenital nystagmus in a Chinese family. Indian J Ophthalmol [serial online] 2016 [cited 2017 Jul 23];64:813-7. Available from: http://www.ijo.in/text.asp?2016/64/11/813/195593

Congenital nystagmus (CN) is characterized by conjugated, spontaneous, and involuntary ocular oscillations. It is an inherited disease and the most common inheritance pattern is X-linked CN. Four-point-one, ezrin, radixin, moesin domain-containing 7 (FRMD7) and G protein-coupled receptor 143 (GPR143) have been identified as the disease-causing genes for X-linked CN.[1],[2] The FRMD7 gene comprises 12 exons and encodes a protein with 714 amino acids. The GPR143 gene consists of 9 exons and encodes a protein with 404 amino acids.

Numerous mutations in FRMD7 gene have been reported since it was first identified in 2006.[3],[4],[5],[6],[7],[8] Mutations in FRMD7 gene are the major causes of Chinese familial X-linked CN and account for approximately 47% of Chinese patients with the disorder.[9]

GPR143 gene is also known as the ocular albinism type 1 (OA1) gene, as mutations in GPR143 also cause OA1.[10] Most patients with OA1 show nystagmus and poor visual acuity. Several reports confirmed the pathogenicity of GPR143 gene in CN family.[2],[11],[12],[13],[14]

In this study, we analyzed the variants in FRMD7 and GPR143 genes in a sixth-generation, nonconsanguineous CN Chinese family. We identified a deletion covering 3-9 exons of GPR143 gene resulting in a truncated protein of 120 residues. Our results expand the spectrum of GPR143 mutations causing CN. This is the first report of molecular characterization in the GPR143 gene in the CN family.


  Methods Top


A sixth-generation Han family from Hebei Province in China including six male patients participated in this study [Figure 1]. The patients underwent complete physical and ophthalmic examinations. The Institutional Review Board approved the project, and investigators followed the principles of the Declaration of Helsinki. Informed consent was obtained from each person. One hundred normal male controls mainly from the north of China were also analyzed.
Figure 1: The pedigree of family. Squares and circles indicate males and females, the darkened symbols represent affected members, dot-marked symbols represent females who carried the mutation, and the patient above the arrow is the proband

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Blood specimens (8 ml) of each family member available were collected in ethylenediaminetetraacetic acid, and genomic DNA was extracted from peripheral blood cells according to a standard protocol (Roche Diagnostics Corporation, Indianapolis, IN, USA). In brief, all the exons and exon-intron boundaries of FRMD7 and GPR143 genes were amplified using the standard polymerase chain reaction (PCR) buffer system with primers listed in [Table 1] and [Table 2]. PCR reactions were performed in a 10 μL volume, containing 1.5 mM MgCl2, 0.4 mM of each primer, 200 μM dNTPs, 1 U Taq DNA polymerase, and 10-20 ng template DNA. Amplification was performed with an initial denaturation for 3 min at 95°C, followed by 30 cycles of denaturation at 95°C for 1 min, annealing at 55°C for 1 min, extension at 72°C for 1 min, and a final extension at 72°C for 3 min. PCR products were purified using a PCR product purification kit (QIAquick; Qiagen, Valencia, CA, USA). The purified PCR products were sequenced using the BigDye Terminator Cycle Sequencing v3.1 kit (Applied Biosystems, Foster City, CA, USA). Briefly, about 10 ng of template DNA was added in each reaction using a temperature program which included 25 cycles of denaturation at 95°C for 30 s, annealing at 50°C for 15 s, and extension at 60°C for 4 min. All samples were analyzed in an ABI Prism 310 Genetic Analyzer (Applied Biosystems, Foster City, CA, USA). The FRMD7 and GPR143 cDNA reference sequence with GenBank accession was used (National Center for Biotechnical Information, Bethesda, Md; available at: http://www.ncbi.nlm.nih.gov).
Table 1: Primers used to amplify the exons of four - point - one, ezrin, radixin, moesin domain - containing 7


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Table 2: Primers used to amplify the exons of G protein - coupled receptor 143


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  Results Top


This sixth-generation pedigree showed a high possibility of an X-linked recessive inheritance pattern [Figure 1]. All patients in this family had various reduced visual acuity with a similar pattern of nystagmus. The type of nystagmus in the family appeared to be jerk nystagmus that manifests as early as at birth. They all had reduced vision, amblyopia, and astigmatism at a different degree. There were normal pigmentation of skin and hair in all patients. Moreover, no retinal pathological changes, optic nerve lesions, any typical sign of OA1, and hypopigmentation of the iris and fundus were detected [Figure 2], [Figure 3], [Figure 4] and [Table 3].
Figure 2: The iris of proband (VI1) in family, (a) right eye, (b) left eye

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Figure 3: Photographs of fundus from proband (VI1) in family, (a) right eye, (b) left eye

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Figure 4: Photographs of OCT from proband (VI1) in family, (a) right eye, (b) left eye

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Table 3: Summary of clinical features of some affected males and carriers


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We sequenced 12 coding exons of FRMD7, 9 coding exons of GPR143, and the adjacent intronic regions of these two genes in the patients. After a complete analysis of the coding sequence of FRMD7 and GPR143, there was no mutation in FRMD7 and no PCR products for the DNA fragments spanning exon 3 to exon 9 of GPR143, suggesting a large deletion in this region [Figure 5].
Figure 5: The polymerase chain reaction results of GPR143 gene. M: marker; E1-E9: exon1-Exon9; C: Represents carrier member; P: Represents affected member

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The mutation was detected in all patients but not found in other unaffected members or in the 100 normal controls. It was predicted to result in a premature stop codon emerged in exon 2, resulting in a truncated protein of only 120 amino acids.


  Discussion Top


Bassi et al. cloned GPR143 gene for OA1 on chromosome Xp22.3.[15] Schiaffino et al. detected various mutations in GPR143 in one-third of X-linked ocular albinism.[10] Sometimes, OA1 can be ignored or misdiagnosed, the ocular disorders should be eliminated before the diagnosis of congenital motor nystagmus is made. X-linked OA1 is characterized by decreased ocular pigmentation, foveal hypoplasia, nystagmus, photodysphoria, and reduced visual acuity. All patients in this family had various reduced visual acuity with nystagmus but there were no retinal pathological changes, optic nerve lesions, or any typical sign of OA1.

We have characterized nystagmus in a sixth-generation Chinese family with a X-linked recessive inheritance pattern. No mutation was identified in the FRMD7 gene and a novel large deletion in exon 3 to exon 9 of the GPR143 gene. All the affected males were hemizygous for the mutation and female carriers were heterozygous for the mutation whereas other normal members of the family had no mutation. These results strongly suggested that the 3-9 exons deletion of GPR143 gene causes the disease in the family.

Until now, more than 100 mutations of GPR143 have been determined, including frameshift deletion and nonsense mutations. Most mutations were reported to cause ocular albinism, but some mutations were reported to cause CN without classical phenotype of ocular albinism.[12],[13]

The human GPR143 gene consists of 9 exons which encode a 439-kDa protein of 404 amino acids with homology to seven transmembrane segments, a GPR. The GPR has been shown to participate in the most common signal transduction system at the plasma membrane. Thus, it suggests that GPR143 mediates signal transduction system and operates at the internal membranes in mammalian cells.[16] Giordano used siRNA inactivation of GPR143 and combined morphological and biochemical methods to investigate melanosomal ultrastructure, melanosomal protein localization, and expression in human pigmented melanocytic cells. The functional loss of GPR143 may lead to decreased pigmentation and causes formation of enlarged aberrant premelanosomes harboring disorganized fibrillar structures and displays proteins of mature melanosomes and lysosomes at their membrane.[17]

We revealed the 7-exons deletion of GPR143 in a Chinese pedigree. The presence of the deletion in all patients and its absence in unaffected members and other 100 unrelated controls indicate that the identified deletion causes CN. The deletion in GPR143 is predicted to result in a truncated protein of 120 amino acid residues, in which the C-terminus of GPR143 protein was deleted.


  Conclusions Top


Our results expand the spectrum of GPR143 mutations causing CN and also confirm the role of GPR143 in the pathogenesis of CN.

Acknowledgments

We are grateful to the patients and their family members for their cooperation in this study. This study was supported by the National Natural Science Foundation (No. 81250039, No. 81300789) and the Beijing Natural Science Foundation (No. 7102160) to L. J. W. The study was approved by the Ethics Committee of the Peking University Third Hospital and conformed to the Declaration of Helsinki.

Financial support and sponsorship

This study was supported by the National Natural Science Foundation (No. 81300789).

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Du W, Bu J, Dong J, Jia Y, Li J, Liang C, et al. A novel frame-shift mutation in FRMD7 causes X-linked idiopathic congenital nystagmus in a Chinese family. Mol Vis 2011;17:2765-8.  Back to cited text no. 1
    
2.
Hu J, Liang D, Xue J, Liu J, Wu L. A novel GPR143 splicing mutation in a Chinese family with X-linked congenital nystagmus. Mol Vis 2011;17:715-22.  Back to cited text no. 2
    
3.
Self JE, Ennis S, Collins A, Shawkat F, Harris CM, Mackey DA, et al. Fine mapping of the X-linked recessive congenital idiopathic nystagmus locus at Xq24-q26.3. Mol Vis 2006;12:1211-6.  Back to cited text no. 3
    
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Zhang B, Liu Z, Zhao G, Xie X, Yin X, Hu Z, et al. Novel mutations of the FRMD7 gene in X-linked congenital motor nystagmus. Mol Vis 2007;13:1674-9.  Back to cited text no. 4
    
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Li N, Wang L, Cui L, Zhang L, Dai S, Li H, et al. Five novel mutations of the FRMD7 gene in Chinese families with X-linked infantile nystagmus. Mol Vis 2008;14:733-8.  Back to cited text no. 5
    
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Fingert JH, Roos B, Eyestone ME, Pham JD, Mellot ML, Stone E. Novel intragenic FRMD7 deletion in a pedigree with congenital X-linked nystagmus. Ophthalmic Genet 2010;31:77-80.  Back to cited text no. 6
    
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Li Y, Pu J, Liu Z, Xu S, Jin F, Zhu L, et al. Identification of a novel FRMD7 splice variant and functional analysis of two FRMD7 transcripts during human NT2 cell differentiation. Mol Vis 2011;17:2986-96.  Back to cited text no. 7
    
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Radhakrishna U, Ratnamala U, Deutsch S, Bartoloni L, Kuracha MR, Singh R, et al. Novel homozygous, heterozygous and hemizygous FRMD7 gene mutations segregated in the same consanguineous family with congenital X-linked nystagmus. Eur J Hum Genet 2012;20:1032-6.  Back to cited text no. 8
    
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He X, Gu F, Wang Z, Wang C, Tong Y, Wang Y, et al. A novel frameshift mutation in FRMD7 causing X-linked idiopathic congenital nystagmus. Genet Test 2008;12:607-13.  Back to cited text no. 9
    
10.
Schiaffino MV, Bassi MT, Galli L, Renieri A, Bruttini M, De Nigris F, et al. Analysis of the OA1 gene reveals mutations in only one-third of patients with X-linked ocular albinism. Hum Mol Genet 1995;4:2319-25.  Back to cited text no. 10
    
11.
Peng Y, Meng Y, Wang Z, Qin M, Li X, Dian Y, et al. A novel GPR143 duplication mutation in a Chinese family with X-linked congenital nystagmus. Mol Vis 2009;15:810-4.  Back to cited text no. 11
    
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Zhou P, Wang Z, Zhang J, Hu L, Kong X. Identification of a novel GPR143 deletion in a Chinese family with X-linked congenital nystagmus. Mol Vis 2008;14:1015-9.  Back to cited text no. 12
    
13.
Liu JY, Ren X, Yang X, Guo T, Yao Q, Li L, et al. Identification of a novel GPR143 mutation in a large Chinese family with congenital nystagmus as the most prominent and consistent manifestation. J Hum Genet 2007;52:565-70.  Back to cited text no. 13
    
14.
Preising M, Op de Laak JP, Lorenz B. Deletion in the OA1 gene in a family with congenital X linked nystagmus. Br J Ophthalmol 2001;85:1098-103.  Back to cited text no. 14
    
15.
Bassi MT, Schiaffino MV, Renieri A, De Nigris F, Galli L, Bruttini M, et al. Cloning of the gene for ocular albinism type 1 from the distal short arm of the X chromosome. Nat Genet 1995;10:13-9.  Back to cited text no. 15
    
16.
Schiaffino MV, d′Addio M, Alloni A, Baschirotto C, Valetti C, Cortese K, et al. Ocular albinism: Evidence for a defect in an intracellular signal transduction system. Nat Genet 1999;23:108-12.  Back to cited text no. 16
    
17.
Giordano F, Bonetti C, Surace EM, Marigo V, Raposo G. The ocular albinism type 1 (OA1) G-protein-coupled receptor functions with MART-1 at early stages of melanogenesis to control melanosome identity and composition. Hum Mol Genet 2009;18:4530-45.  Back to cited text no. 17
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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