This is a rare dysmorphology syndrome that can include Hypothalamic hamartoma (HH), extra digits and other deformities of the hands and feet (postaxial polydactyly and syndactyly), abnormalities of the larynx (bifid epiglottis), imperforate anus, abnormal facial features, and others. Pallister-Hall syndrome is known to be associated with a genetic mutation in the GLI3 gene, which acts as a transcription factor (a regulator protein for turning on and off gene expression). This is a genomic (or genome-wide) mutation, which is to say, a mutation present in every cell in the body

Knowing that Pallister-Hall syndrome is due to a mutation in GLI3, researchers have recently examined the possibility that a somatic (tumor-only) mutation of GLI3 was present in the sporadic HH cases. Using tissue removed at surgery, it was discovered that up to 25% of patients have a somatic mutation of GLI3 in HH tissue. Accordingly, it appears likely that some patients have HH due to a mutation in this gene. It is possible that improved genotyping technology will identify a larger number of GLI3 mutations. It is also likely that other, as yet unidentified mutations in other genes can be responsible. At this time, mutation analysis of GLI3 is not recommended for routine clinical care of patients with HH.