EP263: A pathogenic deletion at 13q32.1q33.1 presenting with bilateral sensorineural hearing loss and pigmentation anomalies, mimicking Waardenburg syndrome

Abstract

13q deletion syndrome is caused by structural and functional monosomy of the long arm of chromosome 13. Individuals with partial deletions of 13q have a wide spectrum of clinical phenotypes, including mild to severe intellectual disability, growth retardation, craniofacial dysmorphism, hand and foot anomalies, brain, cardiac and renal defects. Previous reports suggest that deletions including the 13q32 band are associated with severe congenital malformations. The ZIC2 gene maps to this critical distal region at 13q32.2 and has been considered a possible candidate for brain malformations, such as holoprosencephaly and Dandy-Walker malformation. We present an individual with a 7.9 Mb deletion on chromosome 13, encompassing almost all of band q32, with a relatively mild phenotype. An 11-month-old term male was seen in the medical genetic clinic regarding concerns for possible Waardenburg Syndrome. He presented with bilateral sensorineural hearing loss at 9 months of age and was noted to have multiple hypopigmented lesions on both his feet and chest. Prenatal and post- natal course was unremarkable with normal growth and development. Physical examination revealed mild dysmorphic features such as borderline, low set and posteriorly rotated ears with folded upper helixes and a broad nasal bridge. Hypopigmented lesions consistent with leukoderma was noted over the anterior chest wall, abdominal wall and medial aspect of his right thigh. Family history was positive for a maternal cousin with similar hypopigmented lesions and maternal great, great grandmother with early premature graying of hair. There was no family history of congenital hearing loss or birth defects. A chromosomal microarray (CMA) was performed and revealed a 7.9 megabase pathogenic deletion at chromosome 13q32.1q33.1, involving 65 genes. This deletion encompasses the ZIC2 gene which is associated with holoprosencephaly. This was an unexpected finding and further imaging studies to evaluate for cardiac, renal and brain malformations have been planned. Deletions of 13q are rare and additional cases are needed to better understand the genotype-phenotype correlation. We present an atypical case of a 13q deletion syndrome associated with mild dysmorphism, bilateral sensorineural hearing loss and leukoderma. There have been suggestions that distal deletions are associated with a more severe clinical phenotype and proximal deletions causes less severe major anomalies. This case broadens the clinical spectrum of 13q deletion syndrome as hearing loss is an uncommon finding and dermatological involvement has not been previously reported. There have been one prior report indicating that the loss of Zic2 function results in impaired inner ear development in mice and may be a candidate gene that contributes to the genetics of hearing loss in humans. Additionally, although the region deleted on the long arm of chromosome 13 involves the ZIC2 gene, this patient appears to be growing and developing normally. These findings suggest regions outside of band 13q32 likely contribute to the severe congenital malformations previously associated with distal 13q deletions.