Main clinical features
The KdVS is a multi-system disorder characterized by developmental delay/intellectual disability, neonatal/childhood hypotonia, facial dysmorphism, congenital malformations, and behavioural features.
Prevalence
KdVS is a rare condition. Based on two studies among individuals with unexplained developmental delay (34,616 cases), we estimated the prevalence of the 17q21.31 deletion of 1 in 55 000 individuals (Vulto et al., and Coe et al). The prevalence of the KANSL1 SNV cannot be ascertained with precision yet owing to the limited number of cases identified thus far.More studies are needed to determine an unbiased prevalence of the syndrome.
Inheritance
The KdVS, caused by a microdeletion or a mutation of KANSL1, is inherited in an autosomal dominant manner, but to date almost all cases result from a de novo deletion or KANSL1 mutation. Thus, most affected individuals represent simplex cases, i.e., a single occurrence in a family. The recurrence risk for future pregnancies is low (probably <1%) but greater than that of the general population because of the possibility of germline mosaicism in one of the parents. No individuals with KANSL1-related intellectual disability syndrome have been known to reproduce. Prenatal testing is technically feasible, but the likelihood of recurrence in families who have had an affected child is low.