Expanding the clinical and molecular features of trichorhino- phalangeal syndrome with a novel variant

Background: Tricho-rhino-phalangeal syndrome (TRPS) is a rare, autosomal dominant disorder characterized by typical craniofacial features, ectodermal and skeletal findings. TRPS type 1 (TRPS1) is caused by pathogenic variations in the TRPS1 gene, which relates to the vast majority of cases. TRPS type 2 (TRPS2) is a contiguous gene deletion syndrome involving loss of functional copies of the TRPS1, RAD21, and EXT1. Herein, we reported the clinical and genetic spectrum of seven TRPS patients with a novel variant. We also reviewed the musculoskeletal and radiological findings in the literature.

Methods: Seven Turkish patients (three female, four male) from five unrelated families aged between 7 to 48 years were evaluated. The clinical diagnosis was confirmed by either molecular karyotyping or TRPS1 sequencing analysis via next-generation sequencing.

Results: Both TRPS1 and TRPS2 patients had some common distinctive facial features and skeletal findings. All patients had a bulbous nose with hypoplastic alae nasi, brachydactyly, short metacarpals and phalanges in variable stages. Low bone mineral density (BMD) was identified in two TRPS2 family members presenting with bone fracture, and growth hormone deficiency was detected in two patients. Skeletal X-ray imaging revealed cone-shaped epiphysis of the phalanges in all, and multiple exostoses were present in three patients. Cerebral hamartoma, menometrorrhagia and long bone cysts were among the new/rare conditions. Three pathogenic variants in TRPS1 were identified in four patients from three families, including a frameshift (c.2445dup, p.Ser816GlufsTer28), one missense (c.2762G > A), and a novel splice site variant (c.2700+3A > G). We also reported a familial inheritance in TRPS2 which is known to be very rare.

Conclusions: Our study contributes to the clinical and genetic spectrum of patients with TRPS while also providing a review by comparing with previous cohort studies.