Mutational analysis of HOXD13 and HOXA13 genes in the triphalangeal thumb-brachyectrodactyly syndrome

The Hox genes and their roles in oncogenesis

Hox genes, a highly conserved subgroup of the homeobox superfamily, have crucial roles in development, regulating numerous processes including apoptosis, receptor signalling, differentiation, motility and angiogenesis. Aberrations in Hox gene expression have been reported in abnormal development and malignancy, indicating that altered expression of Hox genes could be important for both oncogenesis and tumour suppression, depending on context. Therefore, Hox gene expression could be important in diagnosis and therapy.

Triphalangeal thumb in association with split hand/foot: A phenotypic marker for SHFM3?

BACKGROUND

At least five distinct loci have been implicated in split hand foot malformation (SHFM). Establishing genotype/phenotype correlations at the chromosomal level may elucidate responsible developmental genes and improve patient management. In our analysis of previously published genetically mapped SHFM cases, preaxial hand involvement was a significant discriminating variable, most commonly seen at the SHFM3 locus (OMIM 600095) at 10q24. Of the 47 SHFM3 patients analyzed, 15 (31.9%) had triphalangeal thumb (TPT), a limb finding not reported at any other locus.

METHODS

The association of TPT/split foot, in particular, prompted us to review the literature for similar cases.

RESULTS

We ascertained a number of unmapped familial and sporadic cases with TPT/split foot, including a group of patients with triphalangeal thumb-brachyectrodactyly syndrome. Certain trends were similar in both SHFM3 and these unmapped literature cases. With respect to gender, 7/12 (58%) of mapped SHFM3 cases with TPT/split foot were male whereas 5/12 (42%) were female, compared with 22/50 (44%) males and 28/50 (56%) females among unmapped cases (P=0.3715). Individuals in both groups usually had bilateral involvement, with 67 and 60% showing bilateral TPT among mapped and literature cases, respectively (P=0.6714). Bilateral involvement of the feet was even more striking (83% of SHFM3 patients and 96% of literature cases; P=0.0808).

CONCLUSIONS

Patients with TPT/split foot may in fact represent SHFM3 cases and should be evaluated for genomic rearrangements at 10q24. TPT may be identified only by radiographic analysis, emphasizing the importance of imaging these patients and their family members.

Split hand malformation, hypospadias, microphthalmia, distinctive face and short stature in two brothers suggest a new syndrome

Split hand/foot malformation (SHFM) is a genetically heterogeneous limb malformation that may be isolated or associated with other malformations. More than 50 recognizable entities with SHFM have been described and at least 5 mapped genetic loci have been implicated. Two brothers with intrauterine growth retardation, short stature, distinctive face, microphthalmia, genital anomalies, and SHFM are described. Molecular analyses of TP63, HOXA13, and HOXD13 genes were normal. We propose this pattern to be a newly recognized SHFM syndrome.

The digits of the wing of birds are 1, 2, and 3. a review

Fossil evidence documenting the evolutionary transition from theropod dinosaurs to birds indicates unambiguously that the digits of the wing of birds are digits 1, 2, and 3. However, some embryological evidence suggests that these digits are 2, 3, and 4. This apparent lack of correspondence has been described as the greatest challenge to the widely accepted theropod-bird link (Zhou 2004. Naturwissenschaften 91:455-471). Here we review the pertinent literature regarding the debate on the origin of birds and wing digital identity and the evidence in favor of a 1, 2, 3 identity of the wing digits. Recent molecular evidence shows that the expression of Hoxd12 and Hoxd13 in the developing wing supports the theropod-bird link. In the chicken foot and in the mouse hand and foot, digit 1 is the only digit to combine the expression of Hoxd13 with the absence of expression of Hoxd12. The same is observed in the anterior digit of the wing, suggesting it is a digit 1, as expected for a theropod. Nevertheless, Galis et al. (2005. J Exp Zool (Mol Dev Evol) in press), argue that Hoxd12 and Hoxd13 expression patterns in mutant limbs do not allow distinguishing the most anterior digit in the bird wing from digit 2. They also argue that constraints to the evolution of limb development support the 2, 3, 4 identity of the wing digits. However, the case put forward by Galis et al. is biased and flawed with regard to interpretation of mutant limbs, developmental mechanisms, stages observed, and the description of the evolutionary variation of limb development. Importantly, Galis et al. do not present evidence from wild-type limbs that counters the conclusions of Vargas and Fallon (2005. J Exp Zool (Mol Dev Evol) 304B(1):85-89), and fail to provide molecular evidence to specifically support the hypothesis that the wing digits are 2, 3, and 4. The expression of Hoxd12 and Hoxd13 in the developing wing is consistent with the hypothesis that birds are living dinosaurs; this view can lead to a greater understanding of the actual limits to the evolutionary variation of limb development.