Exome Sequencing Reveals SLC4A11 Variant Underlying Congenital Hereditary Endothelial Dystrophy (CHED2) Misdiagnosed as Congenital Glaucoma.

Autosomal recessive congenital hereditary endothelial dystrophy (CHED2) may be misdiagnosed as primary congenital glaucoma (PCG) due to similar clinical phenotypes during early infancy. In this study, we identified a family with CHED2, which was previously misdiagnosed as having PCG, and followed up for 9 years. Linkage analysis was first completed in eight PCG-affected families, followed by whole-exome sequencing (WES) in family PKGM3. The following in silico tools were used to predict the pathogenic effects of identified variants: I-Mutant 2.0, SIFT, Polyphen-2, PROVEAN, mutation taster and PhD-SNP. After detecting an SLC4A11 variant in one family, detailed ophthalmic examinations were performed again to confirm the diagnosis. Six out of eight families had CYP1B1 gene variants responsible for PCG. However, in family PKGM3, no variants in the known PCG genes were identified. WES identified a homozygous missense variant c.2024A>C, p.(Glu675Ala) in SLC4A11. Based on the WES findings, the affected individuals underwent detailed ophthalmic examinations and were re-diagnosed with CHED2 leading to secondary glaucoma. Our results expand the genetic spectrum of CHED2. This is the first report from Pakistan of a Glu675Ala variant with CHED2 leading to secondary glaucoma. The p.Glu675Ala variant is likely a founder mutation in the Pakistani population. Our findings suggest that genome-wide neonatal screening is worthwhile to avoid the misdiagnosis of phenotypically similar diseases such as CHED2 and PCG.

Clinical variability of CYP1B1 gene variants in Pakistani primary congenital glaucoma families.

OBJECTIVE: To explore the spectrum of Cytochrome P450 1B1 gene variants and genotype-phenotype correlations in families affected with primary congenital glaucoma. METHODS: The cross-sectional study was performed at the Department of Biotechnology, Lahore College for Women University, Lahore, and the School of Biological Sciences, University of the Punjab, Lahore, Pakistan, from February 2015 to October 2016. Six consanguineous families having individuals affected with primary congenital glaucoma were recruited from different hospitals of the city. Sanger sequencing of coding exon of Cytochrome P450 1B1 gene was performed in order to identify the variants segregating with the disorder. RESULTS: All six families had multiple individuals affected with primary congenital glaucoma. Five out of six families (83%, 5/6) showed CYP1B1 mutations upon Sanger sequencing.All eighteen patients of five families with homozygous Cytochrome P450 1B1 gene variants had different degrees of severity of the phenotypes. Clinical evaluation of the affected members revealed congenital glaucoma with a severe phenotype of corneal oedema, photophobia and corneal scarring. The onset of the phenotype was reported to be congenital but the clinical diagnosis was delayed in four cases since medical help was not sought by the families till much later. CONCLUSIONS: The different degrees of severe phenotypes even in individuals with the same Cytochrome P450 1B1 gene mutation suggested the involvement of modifiers in reducing or increasing the disease severity.

Homozygous p.G61E mutation in a consanguineous Pakistani family with co-existence of juvenile-onset open angle glaucoma and primary congenital glaucoma.

Glaucoma is one of the primary causes of visual impairment and blindness in the world. It is characterized by the damage to the optic nerve head and visual field loss. Variants in CYP1B1 are the most common cause of glaucoma in different world populations. We studied a consanguineous Pakistani family in which three affected individuals had a severe form of glaucoma with members in one generation diagnosed with juvenile-onset open angle glaucoma at 27 years of age, while the members of the next generation were affected with primary congenital glaucoma with onset at birth. Sequencing of CYP1B1 revealed a homozygous transition variant, c.182G>A, p.G61E which co-segregated with the disease phenotype. This variant has been previously reported to cause both recessively and dominantly inherited PCG and JOAG in different populations. However, this reported for the first time in Pakistani PCG and JOAG patients in a homozygous state. This is also the first ever report of a CYP1B1 variant segregating in a consanguineous family with co-existence of JOAG and PCG in two subsequent generations. This observation of different phenotypes due to an identical mutation suggests that primary congenital glaucoma and juvenile-onset open angle glaucoma can both be caused by homozygosity for the same mutation. It also indicates the reduced penetrance of the variant in those affected due to p.G61E mutation and further implies that modifiers have a role in controlling the time of onset of the disorder.