<unk>  has an autosomal dominant pattern of inheritance.<unk>  is a monogenic disorder. The disorder is inherited and controlled by a single pair of genes. A single copy of the mutant gene on an autosome causes HCS. HCS is an autosomal dominant disorder, only one parent with the defective gene is needed to pass the disorder to the offspring. Mutations within the last coding exon of NOTCH2 that remove the PEST domain and escape the nonsense-mediated mRNA decay have been shown to be the main cause of<unk> . The NOTCH2 gene plays a very important role in skeletogenesis. Mutations of NOTCH2 that seem to cause HCS occur in the last coding exon of the gene (exon 34). These mutations remove PEST domains, which mediate proteosomal destruction of the protein. These PEST domains are removed due to the premature stop codon in the amino acid sequence. All HCS alleles are observed to have premature protein destruction before the PEST sequence is fully translated. The result is a mature NOTCH2 gene with a partially completed PEST sequence. In some cases, no PEST sequence at all is seen. This leads to the no proteosomal destruction of the protein. The NOTCH2 gene is ubiquitously expressed in all embryonic tissue. When researching HCS in mice, the homozygous deletion of NOTCH2 leads to death. This observation is important because it explains how the HCS phenotype is not isolated to only one system of the body. NOTCH2 is also shown to regulate RANK-L osteoclastogenesis, which is the production of functional osteoclasts. Osteoclasts are the component that breaks bone down. This is why bone loss is observed in HCS patients, due to the overactivation of RANK-L.
Hajdu–Cheney syndrome
Cleidocranial dysostosis
MEDNIK syndrome
ATR-16 syndrome
Aarskog–Scott syndrome
Treacher Collins syndrome
GRACILE syndrome
Heimler syndrome