PPIP5K2 and PCSK1 are Candidate Genetic Contributors to Familial Keratoconus

Mariam Lotfy Khaled ,Louise F Porter,Alice Liu,Xiaohui Li,Amy Estes,Xiaowen Lu,Barbara A Mysona,Yelena Bykhovskaya,Hongfang Yu,Chunfang Gu,Ryan P Mcnabb,Mitchell A Watsky,Jing Wang,Anthony N Kuo ,E.j Parker ,Michelle Drewry ,Yaron S Rabinowitz,Jerome I Rotter,Sylvia B Smith,Hongyan Xu,Stephen B Shears,Abdulrahman Al-Muammar,Zhong Chen,Khaled K Abu-Amero,Yutao Liu

doi:10.1038/s41598-019-55866-5

Abstract

Keratoconus (KC) is the most common corneal ectatic disorder affecting >300,000 people in the US. KC normally has its onset in adolescence, progressively worsening through the third to fourth decades of life. KC patients report significant impaired vision-related quality of life. Genetic factors play an important role in KC pathogenesis. To identify novel genes in familial KC patients, we performed whole exome and genome sequencing in a four-generation family. We identified potential variants in the PPIP5K2 and PCSK1 genes. Using in vitro cellular model and in vivo gene-trap mouse model, we found critical evidence to support the role of PPIP5K2 in normal corneal function and KC pathogenesis. The gene-trap mouse showed irregular corneal surfaces and pathological corneal thinning resembling KC. For the first time, we have integrated corneal tomography and pachymetry mapping into characterization of mouse corneal phenotypes which could be widely implemented in basic and translational research for KC diagnosis and therapy in the future.

Highlights

Keratoconus (KC, OMIM 14830) is a bilateral, asymmetric corneal degeneration characterized by localized thinning and protrusion of the thinned cornea, which can lead to high myopia, irregular astigmatism, and cornea scarring[1,2]
In the four-generation multiplex family previously linked to chr5q14.3–21.124,37, we selected ten individuals (KC patients: II5, III4, III5, IV4, IV5, IV10, and IV12; controls: III12, III13, and III14) for whole exome sequencing (WES) sequencing (Fig. 1A, with selected individuals indicated by a black arrow)
We found that PPIP5K2 mRNA showed 5-fold higher expression than PPIP5K1 mRNA in human human corneal epithelial cells (HCEC) and human corneal stromal fibroblast (HCSF) cells (Fig. 3A)

Summary

Introduction

Keratoconus (KC, OMIM 14830) is a bilateral, asymmetric corneal degeneration characterized by localized thinning and protrusion of the thinned cornea, which can lead to high myopia, irregular astigmatism, and cornea scarring[1,2]. Genome-wide linkage analyses have identified a number of genomic loci linked with KC These include 1p36.23–36.21, 2p24, 2q13, 3p14-q13, 5q14.3-q21.1, 5q21.2, 5q32-q33, 8q13.1-q21.11, 9q34, 13q32, 14q11.2, 14q24.3, 15q15.1, 15q22.33–24.2, 16q22.3-q23.1, and 20p13-p12.2, 20q1222. C > T was identified in the linkage region 15q22.32–24.2 in a Northern-Irish family who suffered from KC and congenital cataract through targeted sequencing-capture[18,33,34]. Targeted sequencing has been successful in elucidating the causative genetic mutation(s) in numerous inherited diseases such as neurofibromatosis type 1, Marfan syndrome, dilated cardiomyopathy, congenital disorders of glycosylation, and KC35,36. We have successfully used WES and WGS to identify pathogenic variant(s) in a four-generation KC family with a reported linkage locus chr5q14.3–21.1 with autosomal dominant inheritance[24,37]

Methods

Results

Conclusion