Craniometaphyseal dysplasia leading to hydrocephalus and Chiari I malformation

We describe a case of craniometaphyseal dysplasia (CMD) that was initially misdiagnosed as craniodiaphyseal dysplasia (CDD). CMD and CDD are both rare genetic disorders affecting the craniofacial and tubular bones, due to ANKH and SOST gene mutations, respectively, causing similar defects in the control of bone mineralisation.The patient is male, who has been followed longitudinally from birth to his mid-teens, touching on important milestones concerning misdiagnosis and management of CMD. We discuss relevant investigations, diagnosis of ANKH mutation on genetic testing and neurosurgical management, as the patient successfully underwent foramen magnum decompression for secondary Chiari I malformation. We refer to the patient as 'proband' as he is the first in his family diagnosed with a genetic condition.This study highlights the importance of correct identification of the underlying diagnosis as this can affect management. Surgical intervention can be challenging but can successfully manage life-threatening complications of this condition.