Microdeletion and microduplication of 1p36.11p35.3 involving AHDC1 contribute to neurodevelopmental disorder

Abstract

Xia-Gibbs syndrome is a rare genetic condition characterized by intellectual disability, growth retardation, delayed psychomotor development with absent or poor expressive language, distinctive facial features, hypotonia, laryngomalacia and obstructive sleep apnea. At present, Xia-Gibbs syndrome has been reported to be mainly caused by truncating mutations in AHDC1 gene located on chromosome 1p36.11. However, the evidence supporting AHDC1 deletion as a cause of this syndrome is still limited. Here we report an 8-year-old boy carrying a de novo 575 Kb microdeletion at 1p36.11 including AHDC1 gene. The boy is characterized by intellectual disability, developmental delay, short stature, expressive language delay, facial dysmorphism, obstructive sleep apnea and multiple congenital anomalies, which are mostly consistent with the characteristics of Xia-Gibbs syndrome. Therefore, we provide further supporting evidence that AHDC1 deletion causes Xia-Gibbs syndrome through a haploinsufficiency mechanism. Currently, clinical consequences of AHDC1 gene duplication has never been reported. Here, we identify a de novo 480 Kb duplication at 1p36.11p35.3 spanning the entire AHDC1 gene in a 2-year-8-month boy, who displays similar clinical features with that of Xia-Gibbs syndrome, in particular, expressive language delay, hypotonia, laryngomalacia and obstructive sleep apnea, as well as mirrored phenotypes such as overgrowth and advanced bone age. WES test excludes to the degree possible other known genetic causes. This case suggests that AHDC1 gene duplication may be clinical significance.

Keywords: AHDC1 deletion; AHDC1 duplication; Haploinsufficiency; Truncating mutations; Xia-Gibbs syndrome.