Gonioscopy-Assisted Transluminal Trabeculotomy for Myocilin Juvenile Glaucoma

Prevalence of MYOC mutations in a cohort of juvenile open-angle glaucoma (JOAG) patients from Sub-Saharan Africa

PURPOSE

Determine the prevalence and the role of myocilin (MYOC) gene mutations in a sub-Saharan population of juvenile open-angle glaucoma (JOAG) patients DESIGN: Prospective case-control PARTICIPANTS: 45 JOAG patients and 41 normal control subjects from the ophthalmology clinics of the University College Hospital Ibadan, Nigeria.

METHODS

DNA was tested for MYOC coding sequence mutations using Sanger sequencing. Identified mutations were evaluated for pathogenicity by 1) ClinGen scoring 2) assessing prevalence in large public databases of patients with African ancestry (gnomAD and 1000 Genomes); and 3) Mutation analysis algorithms (PolyPhen, SIFT, Blosum62, MutationTaster, CADD, and AlphaMissense). The prevalence of variants was compared between JOAG patients and normal controls from Ibadan using a mutation burden analysis using SKAT-O.

MAIN OUTCOME MEASURES

Sanger DNA sequencing data indicating the presence or absence of glaucoma-causing mutations in the MYOC gene.

RESULTS

A total of 10 instances of 4 MYOC variants were detected. A p.Pro370Leu variant, which has been previously categorized by the ClinGen as Pathogenic, was detected in three (6.7%) of 45 JOAG probands. A p.Arg470Cys MYOC variant, previously categorized a Variant of Unknown Significance, was identified in one (2.2%) of 45 JOAG probands. A p.Glu352Lys variant, previously categorized as Benign, was detected in 2 (4.4%) of JOAG probands. Both the p.Pro370Leu and p.Arg470Cys variants were absent from control subjects and large public databases, while p.Glu352Lys was present at a frequency >1%, which is inconsistent with pathogenicity. Finally, synonymous missense variant, p.Glu396Glu, was also detected. Five of six mutation analysis algorithms supported the pathogenicity of the p.Pro370Leu and p.Arg470Cys variants, while slightly fewer (4 of 6) suggested that p.Glu352Lys is pathogenic.

CONCLUSIONS

MYOC mutations are the most common known cause of JOAG in populations of European ancestry. Our case-control study estimated the prevalence of pathogenic MYOC mutations to be 8.9% in an African population from Nigeria. MYOC mutations are the most common known cause of JOAG in sub-Saharan Africa, however, they account for a minority of cases.

Gonioscopy-Assisted Transluminal Trabeculotomy for Myocilin-Associated Juvenile Open-Angle Glaucoma: A Case Series of 8 Eyes Over 2.2 to 4.1 Years

OBJECTIVE

Mutations within the myocilin (MYOC) gene are the first known single-gene cause of both primary open-angle glaucoma and juvenile open-angle glaucoma (JOAG). Subsequent studies have shown these mutations cause trabecular meshwork dysfunction, resulting in markedly elevated intraocular pressures (IOPs) at young ages. Angle-based procedures, like gonioscopy-assisted transluminal trabeculotomy (GATT), bypass the trabecular meshwork, and as such, are hypothesized to be particularly effective in this angle-based disease. The purpose of this case series is to evaluate the efficacy of GATT for MYOC-associated JOAG.

DESIGN

A retrospective chart review was performed evaluating patients under the age of 18 years with known MYOC-associated JOAG who underwent GATT. A total of 8 eyes of 4 children are included.

PARTICIPANTS

All participants had a strong family history of MYOC glaucoma.

METHODS

All patients underwent a thorough clinical evaluation, including visual acuity, slit lamp examination, optic nerve fundoscopy, and IOP measurements by Goldmann applanation. Most patients also underwent 24-2 Swedish Interactive Thresholding algorithm (SITA) standard Humphrey visual fields and fundus photography, and all patients had retinal nerve fiber layer OCT.

MAIN OUTCOME MEASURES

Main outcome measures include IOP and number of medications. Additional measures include visual acuity, optic nerve photos, visual field testing, and OCT.

RESULTS

Following 360° GATT, all 8 eyes of 4 children had a mean drop in IOP of 26 mmHg (68%), and all were able to stop glaucoma medications entirely. Our patients were followed up between 2.2 and 4.1 years with no evidence of decreasing efficacy or glaucomatous progression. All patients maintain 20/20 visual acuity or better in both eyes, and glaucoma has stabilized on all available ancillary testing (OCT, Humphrey visual field, and optic nerve photos). One patient (patient 4) had a notable reversal of cupping.

CONCLUSIONS

In MYOC-associated JOAG, the pathology is concentrated at the trabecular meshwork (TM), lending itself well to angle-based surgeries, especially GATT. Gonioscopy-assisted transluminal trabeculotomy is particularly effective in children with MYOC JOAG, allowing them to avoid, or at least delay, the need for more invasive surgeries like trabeculectomy and tube shunt surgeries with over 4 years of follow-up. To date, this is the first genetically directed glaucoma surgery available.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

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