Whole Exome Screening Identifies Novel and Recurrent WISP3 Mutations Causing Progressive Pseudorheumatoid Dysplasia in Jammu and Kashmir-India

Abstract

We report identification and genetic characterization of a rare skeletal disorder that remained unidentified for decades in a village of Jammu and Kashmir, India. The population residing in this region is highly consanguineous and a lack of understanding of the disorder has hindered clinical management and genetic counseling for the many affected individuals in the region. We collected familial information and identified two large extended multiplex pedigrees displaying apparent autosomal recessive inheritance of an uncharacterized skeletal dysplasia. Whole exome sequencing (WES) in members of one pedigree revealed a rare mutation in WISP3:c.156C > A (NP_003871.1:p.Cys52Ter), that perfectly segregated with the disease in the family. To our surprise, Sanger sequencing the WISP3 gene in the second family identified a distinct, novel splice site mutation c.643 + 1G > A, that perfectly segregated with the disease. Combining our next generation sequencing data with careful clinical documentation (familial histories, genetic data, clinical and radiological findings), we have diagnosed the families with Progressive Pseudorheumatoid Dysplasia (PPD). Our results underscore the utility of WES in arriving at definitive diagnoses for rare skeletal dysplasias. This genetic characterization will aid in genetic counseling and management, critically required to curb this rare disorder in the families.

Figure 1. Representative Radiographs of Affected from both Families.

(1a) Radiographs of Affected Sibs of Age 9 years and 26 years and Unaffected of Age 22 years. Panels show (a) Hand (b) Radial and Ulnar joints at Elbow (c) Feet (d) Knee Joint (lateral view) (e) Tibia and Fibula at knee joint (Anterior View) (f) Pelvis. (1b) Radiographs of affected individual of 32 years from 2nd family. Panels show (a) Head and Neck (lateral view) (b) Spine Thoracic region (posterior view) (c) Radial and Ulnar joints at Elbow (d) hand (posterior view) (e) Spine (posterior View) (f) Spine (lateral view) (g) Pelvis (h) Knee Joint (lateral view) (i) Foot (lateral view).

Figure 2. Whole Exome Sequencing and Variant Filtering Strategy adapted to narrow down to most promising causative mutation in Family 1.