Joubert Syndrome 27

A number sign (#) is used with this entry because of evidence that Joubert syndrome-27 (JBTS27) is caused by homozygous or compound heterozygous mutation in the B9D1 gene (614144) on chromosome 17p11.

For a phenotypic description and a discussion of genetic heterogeneity of Joubert syndrome, see 213300.

Clinical Features

Romani et al. (2014) reported 2 unrelated children, a 9-year-old boy (COR363) and a 7-year-old girl (COR346), with a relatively mild form of Joubert syndrome. Both had developmental delay, oculomotor abnormalities such as nystagmus or oculomotor apraxia, unspecified dysmorphic features, hypotonia and/or ataxia, and the molar tooth sign on brain imaging. In their table 1, only patient COR363 was noted to have intellectual disability; however, the text suggested that both patients had intellectual disability. Other organ systems were not involved.

Inheritance

The transmission pattern of JBTS27 in the families reported by Romani et al. (2014) was consistent with autosomal recessive inheritance.

Molecular Genetics

In 2 unrelated children with JBTS27, Romani et al. (2014) identified biallelic mutations in the B9D1 gene (614144.0003-614144.0005). The mutations segregated with the disorder in the families and were not found in public databases. Functional studies of the variants and studies of patient cells were not performed. The patients were part of a group of 260 JBTS patients who were screened for mutations in ciliopathy genes.