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Huang N, Wang Q, Bernard RB, Chen CY, Hu JM, Wang JK, Chan KS, Johnson MD, Lin CY. SPINT2 mutations in the Kunitz domain 2 found in SCSD patients inactivate HAI-2 as prostasin inhibitor via abnormal protein folding and N-glycosylation. Hum Mol Genet 2024; 33:752-767. [PMID: 38271183 PMCID: PMC11031362 DOI: 10.1093/hmg/ddae005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2023] [Revised: 11/30/2023] [Accepted: 01/05/2024] [Indexed: 01/27/2024] Open
Abstract
Mutations in the Kunitz-type serine protease inhibitor HAI-2, encoded by SPINT2, are responsible for the pathogenesis of syndromic congenital sodium diarrhea (SCSD), an intractable secretory diarrhea of infancy. Some of the mutations cause defects in the functionally required Kunitz domain 1 and/or subcellular targeting signals. Almost all SCSD patients, however, harbor SPINT2 missense mutations that affect the functionally less important Kunitz domain 2. How theses single amino acid substitutions inactivate HAI-2 was, here, investigated by the doxycycline-inducible expression of three of these mutants in HAI-2-knockout Caco-2 human colorectal adenocarcinoma cells. Examining protein expressed from these HAI-2 mutants reveals that roughly 50% of the protein is synthesized as disulfide-linked oligomers that lose protease inhibitory activity due to the distortion of the Kunitz domains by disarrayed disulfide bonding. Although the remaining protein is synthesized as monomers, its glycosylation status suggests that the HAI-2 monomer remains in the immature, lightly glycosylated form, and is not converted to the heavily glycosylated mature form. Heavily glycosylated HAI-2 possesses full anti-protease activity and appropriate subcellular targeting signals, including the one embedded in the complex-type N-glycan. As predicted, these HAI-2 mutants cannot suppress the excessive prostasin proteolysis caused by HAI-2 deletion. The oligomerization and glycosylation defects have also been observed in a colorectal adenocarcinoma line that harbors one of these SPINT2 missense mutations. Our study reveals that the abnormal protein folding and N-glycosylation can cause widespread HAI-2 inactivation in SCSD patents.
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Affiliation(s)
- Nanxi Huang
- Lombardi Comprehensive Cancer Center, Department of Oncology, Georgetown University, 3970 Reservoir Road NW W422 New Research Building, Washington DC 20057, United States
| | - Qiaochu Wang
- Lombardi Comprehensive Cancer Center, Department of Oncology, Georgetown University, 3970 Reservoir Road NW W422 New Research Building, Washington DC 20057, United States
| | - Robert B Bernard
- Lombardi Comprehensive Cancer Center, Department of Oncology, Georgetown University, 3970 Reservoir Road NW W422 New Research Building, Washington DC 20057, United States
| | - Chao-Yang Chen
- School of Medicine, National Defense Medical Center, No. 161, sec. 6, Minquan E. Road, Neihu Dist. Taipei City 11490, Taiwan, ROC
- Division of Colorectal Surgery, Department of Surgery, Tri-Service General Hospital, No. 325, Sec. 2, Chenggon Road, Neihu Dist. Taipei City 114202, Taiwan, ROC
| | - Je-Ming Hu
- School of Medicine, National Defense Medical Center, No. 161, sec. 6, Minquan E. Road, Neihu Dist. Taipei City 11490, Taiwan, ROC
- Division of Colorectal Surgery, Department of Surgery, Tri-Service General Hospital, No. 325, Sec. 2, Chenggon Road, Neihu Dist. Taipei City 114202, Taiwan, ROC
- Graduate Institute of Medical Sciences, National Defense Medical Center, No. 161, sec. 6, Minquan E. Neihu Dist. Taipei City 11490, Taiwan, ROC
| | - Jehng-Kang Wang
- Department of Biochemistry, National Defense Medical Center, No. 161, sec. 6, Minquan E. Road, Taipei City, 11490, Taiwan, ROC
| | - Khee-Siang Chan
- Department of Intensive Care Medicine, Chi Mei Medical Center, No. 901, Zhonghua Road, Yongkang Dist., Tainan City, 71004, Taiwan, ROC
| | - Michael D Johnson
- Lombardi Comprehensive Cancer Center, Department of Oncology, Georgetown University, 3970 Reservoir Road NW W422 New Research Building, Washington DC 20057, United States
| | - Chen-Yong Lin
- Lombardi Comprehensive Cancer Center, Department of Oncology, Georgetown University, 3970 Reservoir Road NW W422 New Research Building, Washington DC 20057, United States
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Huang N, Wang Q, Chen CY, Hu JM, Wang JK, Chang PY, Johnson MD, Lin CY. N-glycosylation on Asn-57 is required for the correct HAI-2 protein folding and protease inhibitory activity. Glycobiology 2023; 33:203-214. [PMID: 36637420 PMCID: PMC10114645 DOI: 10.1093/glycob/cwad002] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Revised: 12/13/2022] [Accepted: 01/02/2023] [Indexed: 01/14/2023] Open
Abstract
Hepatocyte growth factor activator inhibitor (HAI)-2 is an integral membrane Kunitz-type serine protease inhibitor that regulates the proteolysis of matriptase and prostasin in a cell-type selective manner. The cell-type selective nature of HAI-2 function depends largely on whether the inhibitor and potential target enzymes are targeted to locations in close proximity. The N-glycan moiety of HAI-2 can function as a subcellular targeting signal. HAI-2 is synthesized with 1 of 2 different N-glycan modifications: one of oligomannose-type, which largely remains in the endoplasmic reticulum/GA, and another of complex-type, which is targeted toward the apical surface in vesicle-like structures, and could function as an inhibitor of matriptase and prostasin. HAI-2 contains 2 putative N-glycosylation sites, Asn-57 and Asn-94, point mutations of which were generated and characterized in this study. The protein expression profile of the HAI-2 mutants indicates that Asn-57, and not Asn-94, is responsible for the N-glycosylation of both HAI-2 species, suggesting that the form with oligomannose-type N-glycan is the precursor of the form with complex-type N-glycan. Unexpectedly, the vast majority of non-glycosylated HAI-2 is synthesized into multiple disulfide-linked oligomers, which lack protease inhibitory function, likely due to distorted conformations caused by the disarrayed disulfide linkages. Although forced expression of HAI-2 in HAI-2 knockout cells artificially enhances HAI-2 oligomerization, disulfide-linked HAI-2 oligomers can also be observed in unmodified cells. These results suggest that N-glycosylation on Asn-57 is required for folding into a functional HAI-2 with full protease suppressive activity and correct subcellular targeting signal.
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Affiliation(s)
- Nanxi Huang
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC 20057, United States
| | - Qiaochu Wang
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC 20057, United States
| | - Chao-Yang Chen
- School of Medicine, National Defense Medical Center, Taipei 114, Taiwan, ROC
- Division of Colorectal Surgery, Department of Surgery, Tri-Service General Hospital, Taipei 114, Taiwan, ROC
| | - Je-Ming Hu
- School of Medicine, National Defense Medical Center, Taipei 114, Taiwan, ROC
- Division of Colorectal Surgery, Department of Surgery, Tri-Service General Hospital, Taipei 114, Taiwan, ROC
- Graduate Institute of Medical Sciences, National Defense Medical Center, Taipei 114, Taiwan, ROC
| | - Jehng-Kang Wang
- Department of Biochemistry, National Defense Medical Center, Taipei 114, Taiwan, ROC
| | - Ping-Ying Chang
- School of Medicine, National Defense Medical Center, Taipei 114, Taiwan, ROC
- Division of Hematology/Oncology, Department of internal medicine, Tri-Service General Hospital, Taipei 114, Taiwan, ROC
| | - Michael D Johnson
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC 20057, United States
| | - Chen-Yong Lin
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC 20057, United States
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Zhang XX, Chen X, Zhou W, Mavratsas VC, Xiao YY, Tan XR, Zheng SJ, Zhang XX. A novel SPINT2 missense mutation causes syndromic congenital sodium diarrhea. World J Pediatr 2022; 18:861-865. [PMID: 36123503 DOI: 10.1007/s12519-022-00613-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2022] [Accepted: 08/19/2022] [Indexed: 11/26/2022]
Affiliation(s)
- Xian-Xu Zhang
- Department of Pediatrics, the Second Xiangya Hospital, Central South University, Changsha, 410011, China
| | - Xi Chen
- Department of Pediatrics, the Second Xiangya Hospital, Central South University, Changsha, 410011, China
| | - Wei Zhou
- Wuhan Primbio Medical Laboratory, Wuhan, 430075, China
| | | | - Yang-Yang Xiao
- Department of Pediatrics, the Second Xiangya Hospital, Central South University, Changsha, 410011, China
| | - Xin-Rui Tan
- Department of Pediatrics, the Second Xiangya Hospital, Central South University, Changsha, 410011, China
| | - Song-Jia Zheng
- Department of Pediatrics, the Second Xiangya Hospital, Central South University, Changsha, 410011, China
| | - Xing-Xing Zhang
- Department of Pediatrics, the Second Xiangya Hospital, Central South University, Changsha, 410011, China.
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The genetics of monogenic intestinal epithelial disorders. Hum Genet 2022; 142:613-654. [PMID: 36422736 PMCID: PMC10182130 DOI: 10.1007/s00439-022-02501-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2022] [Accepted: 10/23/2022] [Indexed: 11/27/2022]
Abstract
Monogenic intestinal epithelial disorders, also known as congenital diarrheas and enteropathies (CoDEs), are a group of rare diseases that result from mutations in genes that primarily affect intestinal epithelial cell function. Patients with CoDE disorders generally present with infantile-onset diarrhea and poor growth, and often require intensive fluid and nutritional management. CoDE disorders can be classified into several categories that relate to broad areas of epithelial function, structure, and development. The advent of accessible and low-cost genetic sequencing has accelerated discovery in the field with over 45 different genes now associated with CoDE disorders. Despite this increasing knowledge in the causal genetics of disease, the underlying cellular pathophysiology remains incompletely understood for many disorders. Consequently, clinical management options for CoDE disorders are currently limited and there is an urgent need for new and disorder-specific therapies. In this review, we provide a general overview of CoDE disorders, including a historical perspective of the field and relationship to other monogenic disorders of the intestine. We describe the genetics, clinical presentation, and known pathophysiology for specific disorders. Lastly, we describe the major challenges relating to CoDE disorders, briefly outline key areas that need further study, and provide a perspective on the future genetic and therapeutic landscape.
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Impaired Intestinal Sodium Transport in Inflammatory Bowel Disease: From the Passenger to the Driver's Seat. Cell Mol Gastroenterol Hepatol 2021; 12:277-292. [PMID: 33744482 PMCID: PMC8165433 DOI: 10.1016/j.jcmgh.2021.03.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Revised: 03/09/2021] [Accepted: 03/09/2021] [Indexed: 12/22/2022]
Abstract
Although impaired intestinal sodium transport has been described for decades as a ubiquitous feature of inflammatory bowel disease (IBD), whether and how it plays a pivotal role in the ailment has remained uncertain. Our identification of dominant mutations in receptor guanylyl cyclase 2C as a cause of IBD-associated familial diarrhea syndrome brought a shift in the way we envision impaired sodium transport. Is this just a passive collateral effect resulting from intestinal inflammation, or is it a crucial regulator of IBD pathogenesis? This review summarizes the mutational spectrum and underlying mechanisms of monogenic IBD associated with congenital sodium diarrhea. We constructed a model proposing that impaired sodium transport is an upstream pathogenic factor in IBD. The review also synthesized emerging insights from microbiome and animal studies to suggest how sodium malabsorption can serve as a unifying mediator of downstream pathophysiology. Further investigations into the mechanisms underlying salt and water transport in the intestine will provide newer approaches for understanding the ion-microbiome-immune cross-talk that serves as a driver of IBD. Model systems, such as patient-derived enteroids or induced pluripotent stem cell models, are warranted to unravel the role of individual genes regulating sodium transport and to develop more effective epithelial rescue and repair therapies.
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Ernst J, Hiasat J, Alabek ML, Scanga HL, Motley W, Nischal KK. Expansion of the ophthalmic phenotype of SPINT2-related syndromic congenital sodium diarrhea. Am J Med Genet A 2021; 185:1270-1274. [PMID: 33547739 DOI: 10.1002/ajmg.a.62094] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2020] [Revised: 01/08/2021] [Accepted: 01/12/2021] [Indexed: 11/08/2022]
Abstract
A 5-year-old girl presented with treatment-refractory dry eye and recurrent episodes of eye pain. She had been previously diagnosed with syndromic congenital sodium diarrhea (SCSD) caused by a pathogenic variant in SPINT2. Her local pediatric ophthalmologist had made the diagnosis of severe dry eye with corneal erosions, based on which, we arranged an eye exam under anesthesia (EUA) and punctal plug placement. Anterior segment optical coherence tomography (OCT) and corneal photographs were taken during the procedure. There are reports describing similar ophthalmic findings in this syndrome. However, to the best of our knowledge, this is the first case report to document OCT imaging and corneal photographs in a patient with SCSD, which we feel expands the ophthalmic phenotype of this rare genetic disorder.
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Affiliation(s)
- Julia Ernst
- Eye Center, UPMC Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania, USA.,The Division of Pediatric Ophthalmology, Strabismus and Adult Motility, UPMC Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania, USA.,Medical University of Warsaw, Warsaw, Poland
| | - Jamila Hiasat
- Eye Center, UPMC Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania, USA.,The Division of Pediatric Ophthalmology, Strabismus and Adult Motility, UPMC Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Michelle L Alabek
- Eye Center, UPMC Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania, USA.,The Division of Pediatric Ophthalmology, Strabismus and Adult Motility, UPMC Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Hannah L Scanga
- Eye Center, UPMC Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania, USA.,The Division of Pediatric Ophthalmology, Strabismus and Adult Motility, UPMC Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - William Motley
- Division of Pediatric Ophthalmology, Cincinnati Children's Hospital, Cincinnati, Ohio, USA
| | - Ken K Nischal
- Eye Center, UPMC Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania, USA.,The Division of Pediatric Ophthalmology, Strabismus and Adult Motility, UPMC Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania, USA.,School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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Tufting Enteropathy: A Review of Clinical and Histological Presentation, Etiology, Management, and Outcome. Gastroenterol Res Pract 2020; 2020:5608069. [PMID: 33029133 PMCID: PMC7530495 DOI: 10.1155/2020/5608069] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/12/2020] [Revised: 09/04/2020] [Accepted: 09/15/2020] [Indexed: 02/07/2023] Open
Abstract
Congenital tufting enteropathy (CTE), also named intestinal epithelial dysplasia, is a rare, autosomal recessive enteropathy with persistent and life-threatening intractable diarrhea early in life. Intractable diarrhea is present independent of breast or formula feeding. Most CTE patients require total parenteral nutrition (TPN), and in severe cases, small bowel transplantation is needed. In the last decade, we have seen remarkable progress in certain aspects, such as the pathogenesis and diagnostic methods of the disease. Rapidly developing molecular analysis techniques have improved the diagnostic methods for CTE and reduced invasive and expensive procedures. Mutations in the gene encoding human epithelial cell adhesion molecule (EpCAM) were identified in the typical form of CTE, which usually exhibits isolated refractory diarrhea. Moreover, the syndromic form of CTE features anal and choanal atresias as well as ophthalmologic signs, which are associated with mutations in the gene encoding Serine Peptidase Inhibitor Kunitz Type 2 (SPINT2). This article reviews CTE disease based on its clinical and histological presentation, etiology and pathogenesis, and management and outcome.
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Holt-Danborg L, Vodopiutz J, Nonboe AW, De Laffolie J, Skovbjerg S, Wolters VM, Müller T, Hetzer B, Querfurt A, Zimmer KP, Jensen JK, Entenmann A, Heinz-Erian P, Vogel LK, Janecke AR. SPINT2 (HAI-2) missense variants identified in congenital sodium diarrhea/tufting enteropathy affect the ability of HAI-2 to inhibit prostasin but not matriptase. Hum Mol Genet 2020; 28:828-841. [PMID: 30445423 DOI: 10.1093/hmg/ddy394] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2018] [Revised: 11/07/2018] [Accepted: 11/08/2018] [Indexed: 11/13/2022] Open
Abstract
The syndromic form of congenital sodium diarrhea (SCSD) is caused by bi-allelic mutations in SPINT2, which encodes a Kunitz-type serine protease inhibitor (HAI-2). We report three novel SCSD patients, two novel SPINT2 mutations and review published cases. The most common findings in SCSD patients were choanal atresia (20/34) and keratitis of infantile onset (26/34). Characteristic epithelial tufts on intestinal histology were reported in 13/34 patients. Of 13 different SPINT2 variants identified in SCSD, 4 are missense variants and localize to the second Kunitz domain (KD2) of HAI-2. HAI-2 has been implicated in the regulation of the activities of several serine proteases including prostasin and matriptase, which are both important for epithelial barrier formation. No patient with bi-allelic stop mutations was identified, suggesting that at least one SPINT2 allele encoding a protein with residual HAI-2 function is necessary for survival. We show that the SCSD-associated HAI-2 variants p.Phe161Val, p.Tyr163Cys and p.Gly168Ser all display decreased ability to inhibit prostasin-catalyzed cleavage. However, the SCSD-associated HAI-2 variants inhibited matriptase as efficiently as the wild-type HAI-2. Homology modeling indicated limited solvent exposure of the mutated amino acids, suggesting that they induce misfolding of KD2. This suggests that prostasin needs to engage with an exosite motif located on KD2 in addition to the binding loop (Cys47/Arg48) located on the first Kunitz domain in order to inhibit prostasin. In conclusion our data suggests that SCSD is caused by lack of inhibition of prostasin or a similar protease in the secretory pathway or on the plasma membrane.
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Affiliation(s)
- Lasse Holt-Danborg
- Department of Cellular and Molecular Medicine, The Panum Institute, University of Copenhagen, Denmark
| | - Julia Vodopiutz
- Department of Pediatrics and Adolescent Medicine, Medical University of Vienna, Vienna
| | - Annika W Nonboe
- Department of Cellular and Molecular Medicine, The Panum Institute, University of Copenhagen, Denmark
| | - Jan De Laffolie
- Abteilung Allgemeine Pädiatrie und Neonatologie, Zentrum für Kinderheilkunde und Jugendmedizin, Justus-Liebig-Universität, Gießen, Germany
| | - Signe Skovbjerg
- Department of Cellular and Molecular Medicine, The Panum Institute, University of Copenhagen, Denmark
| | - Victorien M Wolters
- Department of Pediatric Gastroenterology, WKZ/ UMC Utrecht, Utrecht, The Netherlands
| | - Thomas Müller
- Department of Pediatrics I, Medical University of Innsbruck, Innsbruck, Austria
| | - Benjamin Hetzer
- Department of Pediatrics I, Medical University of Innsbruck, Innsbruck, Austria
| | - Alexander Querfurt
- Gesundheit Nord gGmbH, Klinikverbund Bremen, Klinik für Kinder und Jugendmedizin, Professor-Hess-Kinderklinik, Klinikum Bremen-Mitte, Bremen, Germany
| | - Klaus-Peter Zimmer
- Abteilung Allgemeine Pädiatrie und Neonatologie, Zentrum für Kinderheilkunde und Jugendmedizin, Justus-Liebig-Universität, Gießen, Germany
| | - Jan K Jensen
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Andreas Entenmann
- Department of Pediatrics I, Medical University of Innsbruck, Innsbruck, Austria
| | - Peter Heinz-Erian
- Department of Pediatrics I, Medical University of Innsbruck, Innsbruck, Austria
| | - Lotte K Vogel
- Department of Cellular and Molecular Medicine, The Panum Institute, University of Copenhagen, Denmark
| | - Andreas R Janecke
- Department of Pediatrics I, Medical University of Innsbruck, Innsbruck, Austria.,Division of Human Genetics, Medical University of Innsbruck, Innsbruck, Austria
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George A, Cogliati T, Brooks BP. Genetics of syndromic ocular coloboma: CHARGE and COACH syndromes. Exp Eye Res 2020; 193:107940. [PMID: 32032630 DOI: 10.1016/j.exer.2020.107940] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Revised: 01/20/2020] [Accepted: 01/22/2020] [Indexed: 02/07/2023]
Abstract
Optic fissure closure defects result in uveal coloboma, a potentially blinding condition affecting between 0.5 and 2.6 per 10,000 births that may cause up to 10% of childhood blindness. Uveal coloboma is on a phenotypic continuum with microphthalmia (small eye) and anophthalmia (primordial/no ocular tissue), the so-called MAC spectrum. This review gives a brief overview of the developmental biology behind coloboma and its clinical presentation/spectrum. Special attention will be given to two prominent, syndromic forms of coloboma, namely, CHARGE (Coloboma, Heart defect, Atresia choanae, Retarded growth and development, Genital hypoplasia, and Ear anomalies/deafness) and COACH (Cerebellar vermis hypoplasia, Oligophrenia, Ataxia, Coloboma, and Hepatic fibrosis) syndromes. Approaches employed to identify genes involved in optic fissure closure in animal models and recent advances in live imaging of zebrafish eye development are also discussed.
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Affiliation(s)
- Aman George
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health. Bethesda, Maryland, 20892, USA
| | - Tiziana Cogliati
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health. Bethesda, Maryland, 20892, USA
| | - Brian P Brooks
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health. Bethesda, Maryland, 20892, USA.
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