A Novel Compound Heterozygous Variant in the ABHD12 Gene Cause PHARC Syndrome in a Chinese Family: The Proband Presenting New Genotype and Phenotype.

Abstract

Background: PHARC syndrome, a rare autosomal recessive neurodegenerative disorder caused by mutations in the ABHD12 gene, is characterized by demyelinating polyneuropathy, hearing loss, ataxia, retinitis pigmentosa (RP), and early-onset cataracts. If patients are first diagnosed in the ophthalmology department, they are easily misdiagnosed as having RP or Usher syndrome. This study aimed to identify the genetic etiology and determine the clinical diagnosis of a Chinese family with suspected PHARC syndrome.

Method: Comprehensive ophthalmic examinations and systemic evaluations were conducted to confirm the phenotype. The genotype was identified through Whole Exome Sequencing (WES), and the current literature was reviewed understand better manifestations of PHARC syndrome related to pathogenic variants.

Results: The principal symptoms of the proband comprised profound sensorineural hearing loss since childhood, severe visual impairment, congenital cataracts, cone-rod dystrophy, and ataxia. WES revealed that the proband carried a compound heterozygous variant in the ABHD12 gene: M1, a known nonsense variation c.477G > A (p.Trp159Ter); and M2, a novel copy number variant with a deletion of approximately 18.10 Kbp in chromosome 20p11.21 (seq[GRCh38]del(20) (p11.21)chr20:g. 25302218_25320318del), covering exons 4-12 of the ABHD12 gene. The literature review indicated that there were 65 patients with PHARC from 30 different families. All clinical information of the described patients with PHARC syndrome and all known mutations associated with the disease to date were compiled.

Conclusion: This study expands the spectrum of pathogenic variants and phenotype for PHARC syndrome and suggests genetic testing is necessary for a definitive diagnosis of PHARC syndrome.