AB097. Clinical and molecular characterization of patients with 6p25 deletion syndrome

Objective: Chromosomal imbalances and rearrangements have been implicated in the etiology of intellectual disability and congenital anomalies. Many of these imbalances are caused by submicroscopic deletions or duplications not detected through conventional cytogenetic analysis. The advances in technology for detecting copy number changes, most notably chromosomal microarray analysis (CMA) has allowed the detection of these submicroscopic deletions or duplications. Submicroscopic 6p25 deletion is now recognized as a clinically identifiable syndrome. Clinical features in this syndrome include intellectual disability, developmental delay, hypotonia, sensorineural hearing loss, midface hypoplasia, ocular anomalies, cardiac defects and varying central nervous system anomalies. The aim of this report is to describe the phenotypic range of individuals with 6p25 deletion syndrome in the South East Asian population.

Methods: We reviewed the records of patients who are follow up in the Genetics clinic at KK Women’s and Children’s Hospital (KKH) and have CMA carried out using the Agilent 4×400 K and 4×180 K CGH+SNP catalogue array at KK Research Centre and DNA Diagnostic & Research Laboratory, respectively.

Results: We provide detailed molecular cytogenetic descriptions and clinical presentation of four unrelated patients with submicroscopic 6p25 deletion syndrome. Patient 1 has 5.1 Mb deletion (chr6: 224,712-5,352,662 hg19), while Patient 2 has 2 Mb deletion (chr6: 381,537-2,408,671 hg19). Patient 3 has 1.2 Mb deletion (chr6:1,486,461-2,692,219 hg19) and Patient 4 has 4.1 Mb deletion (chr6: 206,749-4,320,368 hg19). All of these patients have congenital heart defects, developmental delay, dysmorphic features and additional phenotypic abnormalities: Patient 1 has sensorineural hearing loss, hernia, bilateral undescended testes and buried penis, while Patient 2 has mild intellectual disability, bilateral mixed hearing loss, microphthalmia and submucous cleft palate. Patient 3 has congenital glaucoma, corneal clouding, hydrocephalus and ventriculomegaly, while Patient 4 has congenital glaucoma, micropenis, hearing loss and hypotonia.

Conclusions: Our result supports the notion that the genes responsible for the physical phenotype reside in the 6p25.1 region. Our results also reiterate the benefits of CMA in identifying these submicroscopic copy number variants, establishing new phenotype-genotype correlation in known syndromes and refining previously established ones.

Keywords: 6p25 deletion syndrome; chromosomal microarray analysis (CMA); developmental delay; KK Women’s and Children’s Hospital (KKH)