Definition:

Antley-Bixler syndrome (ABS) is a rare craniosynostosis syndrome characterized by radiohumeral synostosis. There is a wide spectrum of anomalies seen in ABS. Other features include midface hypoplasia, choanal stenosis or atresia, and multiple joint contractures. Two genetically distinctive forms have been observed. Type 1 ABS involves mutations in the FGFR2 gene without impairment of steroidogenesis. Type 1 ABS patients are with the most severe skeletal abnormalities but normal genitalia. Type 2 ABS involves mutations in the gene encoding cytochrome P450 oxidoreductase (POR), an enzyme which plays a direct role in steroidogenesis. Type 2 ABS is an autosomal recessive disorder, and it is associated with abnormal genitalia in both sexes due to impaired steroidogenesis. Mortality has been reported to be as high as 80% in the neonatal period, primarily due to airway compromise, and prognosis improves with increasing age.