A mother and daughter with a novel phenotype of hand and foot abnormalities and severe pectus excavatum

The Developmental Phenotype of the Great Toe in Fibrodysplasia Ossificans Progressiva

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder in which extensive heterotopic ossification (HO) begins to form during early childhood and progresses throughout life. Although HO does not occur during embryonic development, children who carry the ACVR1^R206H mutation that causes most cases of FOP characteristically exhibit malformation of their great toes at birth, indicating that the mutation acts during embryonic development to alter skeletal formation. Despite the high prevalence of the great toe malformation in the FOP population, it has received relatively little attention due to its clinically benign nature. In this study, we examined radiographs from a cohort of 41 FOP patients ranging from 2 months to 48 years of age to provide a detailed analysis of the developmental features, progression, and variability of the great toe malformation of FOP, which include absent skeletal structures, malformed epiphyses, ectopic ossification centers, malformed first metatarsals and phalangeal fusion.

Radiography of Chitayat syndrome in an infant male

Chitayat syndrome is a rare genetic syndrome characterised by bilateral hyperphalangism, bronchomalacia, hallux valgus, and other facial dysmorphism including large anterior fontanelle, hypertelorism, and anteverted nostrils. Since the initial discovery, only few cases of Chitayat syndrome have been reported in the literature. Previous literatures showed the genetic link between 5 case reports, showing that a unique link of recurrent c.266A>G p.(Tyr89Cys) variant in the ERF gene may be the contributory genetic cause of Chitayat syndrome. However, it still remains as an unfamiliar genetic syndrome. In this case report, we aim to discuss a rare case of Chitayat syndrome and demonstrate the radiological findings associated.

Chitayat syndrome: hyperphalangism, characteristic facies, hallux valgus and bronchomalacia results from a recurrent c.266A>G p.(Tyr89Cys) variant in the ERF gene

BACKGROUND

In 1993, Chitayat et al., reported a newborn with hyperphalangism, facial anomalies, and bronchomalacia. We identified three additional families with similar findings. Features include bilateral accessory phalanx resulting in shortened index fingers; hallux valgus; distinctive face; respiratory compromise.

OBJECTIVES

To identify the genetic aetiology of Chitayat syndrome and identify a unifying cause for this specific form of hyperphalangism.

METHODS

Through ongoing collaboration, we had collected patients with strikingly-similar phenotype. Trio-based exome sequencing was first performed in Patient 2 through Deciphering Developmental Disorders study. Proband-only exome sequencing had previously been independently performed in Patient 4. Following identification of a candidate gene variant in Patient 2, the same variant was subsequently confirmed from exome data in Patient 4. Sanger sequencing was used to validate this variant in Patients 1, 3; confirm paternal inheritance in Patient 5.

RESULTS

A recurrent, novel variant NM_006494.2:c.266A>G p.(Tyr89Cys) in ERF was identified in five affected individuals: de novo (patient 1, 2 and 3) and inherited from an affected father (patient 4 and 5). p.Tyr89Cys is an aromatic polar neutral to polar neutral amino acid substitution, at a highly conserved position and lies within the functionally important ETS-domain of the protein. The recurrent ERF c.266A>C p.(Tyr89Cys) variant causes Chitayat syndrome.

DISCUSSION

ERF variants have previously been associated with complex craniosynostosis. In contrast, none of the patients with the c.266A>G p.(Tyr89Cys) variant have craniosynostosis.

CONCLUSIONS

We report the molecular aetiology of Chitayat syndrome and discuss potential mechanisms for this distinctive phenotype associated with the p.Tyr89Cys substitution in ERF.