Use of the term "Antley-Bixler syndrome": minimizing confusion.

To the Editor: We read with great interest the publication by Huang et al. (2005), which made a number of significant contributions to our understanding of the biochemistry and molecular genetics of a newly described, highly variable, autosomal recessive condition referred to as “cytochrome P450 oxidoreductase (POR [MIM 124015]) deficiency.” We agree with the authors that what has been termed “Antley-Bixler syndrome” (ABS [MIM 207410]) in the scientific literature is genetically heterogeneous with at least two distinct disorders, (1) ABS without disordered steroidogenesis, which appears to be a variant of the autosomal dominant fibroblast growth factor receptor (FGFR)–related craniosynostosis syndromes, and (2) ABS with disordered steroidogenesis, which appears to be caused by severe mutations in POR. However, we disagree with the authors’ proposition “that the term ‘ABS’ be reserved for those patients with the skeletal dysmorphologic findings initially reported by Antley and Bixler (1975) but who have normal genitalia and normal steroidogenesis, and that patients with the skeletal dysmorphologic phenotype plus evidence of disordered steroidogenesis be referred to as having ‘POR deficiency’” (Huang et al. 2005, p. 745). Although the female patient first described by Antley and Bixler did not have ambiguous genitalia or any reported steroid anomalies, there are a number of reasons why these facts do not provide sufficient justification to reserve the term “ABS” for patients with FGFR mutations. These include: 1. To our knowledge, the patient described by Antley and Bixler (1975) has not had molecular testing for mutations in FGFR2 or POR. Therefore, POR deficiency cannot be ruled out for this patient. 2. Steroid abnormalities associated with POR deficiency and ABS are not always recognized without the use of urinary steroid profiling (Shackleton et al. 2004). In fact, Huang et al. (2005) found POR mutations in both alleles of two female patients with ABS who were initially believed not to have steroid abnormalities when first reported by Reardon et al. (2000). 3. The presence of ambiguous genitalia is not necessary for making a diagnosis of POR deficiency. This is illustrated by the two females with ABS and normal genitalia who are reported by Huang et al. (2005) to have mutations in POR. In addition, we have published a family with classic ABS in which a male child had ambiguous genitalia but his sister did not (Cragun et al. 2004). Both children had evidence of abnormal steroid metabolism, and mutations in POR have subsequently been confirmed. Because of similarities with respect to phenotype, molecular findings, and pattern of inheritance, patients with FGFR mutations should be grouped with those with the other autosomal dominant FGFR-related craniosynostosis syndromes. This proposal is supported by others who have questioned the diagnosis of ABS for a patient who has FGFR2 mutations (Gorlin 1999; Gripp et al. 1999). Even Huang et al. (2005) admit that the diagnosis of ABS was reconsidered in some of the patients they report with FGFR mutations. Clarifying which individuals represent classic ABS has been difficult because few pictures of patients with ABS and known POR or FGFR mutations have been published, and the clinical descriptions of these patients often lack detail. However, some subtle features—including a pear-shaped or bulbous nose, low-set and dysplastic ears, arachnodactyly, and/or rockerbottom feet—are often present in patients with ABS who are known or suspected to have POR deficiency; these features are not described in patients with known FGFR mutations. Interestingly, the patient reported by Antley and Bixler (1975) had a bulbous nose, low-set dysplastic ears, and arachnodactyly. In addition, that patient also had significant camptodactyly, which is described in patients who likely have POR deficiency more commonly than in those with FGFR mutations. Compared with cases of ABS that are suspected or known to be caused by POR deficiency, patients with FGFR mutations generally have more-severe proptosis and facial dysmorphism that is more similar to that of patients with Pfeiffer syndrome or Crouzon syndrome (two FGFR-related craniosynostosis syndromes). On the basis of this evidence, the authors’ conclusion—that “aside from the genital anomalies attributable to disordered steroidogenesis, no morphologic feature distinguished patients with POR mutations from those with FGFR mutations” (Huang et al. 2005, p. 736)—may not be warranted. Continuing to use the term “ABS” for patients with FGFR mutations will only contribute to the confusion that is already present in the literature. The concern is that this confusion may interfere with proper patient management and counseling, both of which depend on the ability of clinicians and researchers to clearly recognize, understand, and convey to patients the differences between POR deficiency and FGFR-related craniosynostosis syndromes. Use of the term “ABS” to describe patients with POR deficiency who are at the more severe end of the phenotypic spectrum can be clinically useful in distinguishing them from patients with POR deficiency who have mild or no skeletal defects (Arlt et al. 2004; Fluck et al. 2004; Fukami et al. 2004). We believe it would be better to reserve the use of the term “ABS” for patients with POR deficiency and clinically significant craniosynostosis and/or radiohumoral synostosis.