Comprehensive analysis of clinical spectrum and genotype associations in Chinese and literature reported KBG syndrome.

BACKGROUND

Patients with KBG Syndrome due to ANKRD11 mutations and 16q24.3 microdeletions including ANKRD11 were identified. Classical and most frequent phenotypes include various degrees of intelligence disability (ID), short stature (SS), delayed bone age, macrodontia, distinctive facial features and skeletal anomalies. The variable expressivity of KBG syndrome makes it challenging to establish genotype-phenotype correlations, which also affects further studies for this novel syndrome. We aim to report three unrelated patients with KBG syndrome caused by ANKRD11 gene pathological variants and to evaluate potential associations among ANKRD11 gene variant types, the 16q24.3 microdeletion, and the clinical spectrum of KBG syndrome.

METHODS

The genetic etiology of three unreported KBG patients was identified by whole exome sequencing and confirmed via Sanger sequencing. Literature review was conducted to summarize the phenotype-genotype relationship based on three unreported Chinese cases and 186 reported cases.

RESULTS

Two pathological variants (c.7407dupC, p.P2530Rfs*61; c.G3046A, p.D1016N) and one reported variant (c.6792dupC, p. P2271Pfs*8) were detected in our patients. Compared with the 16q24.3 microdeletion, patients harboring ANKRD11 gene mutations showed significantly higher frequency of malformations including macrodontia, long philtrum, abnormal eyebrows, widely spaced eyes, anteverted nares, eyelid ptosis, brachydactyly, brachycephaly (P<0.05), and significantly lower risk of congenital heart diseases and frontal bossing (P<0.05). The intellectual disability (ID) was significantly milder among patients carrying truncating variants located between repression domain 1 (RD1) and activation domain (AD) than those carrying mutations disrupting repression domain 2 (RD2) alone and disrupting all functional domain (RD1, AD or RD2) (P<0.05).

CONCLUSIONS

Novel pathological variants harbored in the ANKRD11 gene contribute to the KBG syndrome variant spectrum. ANKRD11 gene variants disrupting RD1 and RD2 or RD2 alone are more likely to have more severe ID, which warrants different intervention strategies for KBG syndrome.