Preaxial polydactyly is less frequent than postaxial one (but could be more frequent in Caucasians). When present, one should search for an associated syndrome (particularly if a triphalangeal thumb is present), such as Holt-Oram syndrome (atrial and ventricular septal defects, abnormal thumb - from absent to triphalangeal), short ribs polydactyly syndromes, Carpenter syndrome, trisomy 21, VACTERL association, Fanconi, etc.

Classification

 PPD1: preaxial polydactyly type 1 (thumb polydactyly) (MIM.174400)

• thumb polydactyly involves duplication of one or more of the skeletal components of a biphalangeal thumb. Severity varies from mere broadening of the distal phalanx with slight bifurcation at the tip to full duplication of the thumb including the metacarpals.
   PPD2 at 7q36: preaxial polydactyly type 2 (polydactyly of a triphalangeal thumb) (MIM.174500)
   PPD3: preaxial polydactyly type 3: polydactyly of an index finger (MIM.174600)
   PPD4 at 7p13: preaxial polydactyly type 4: polysyndactyly (MIM.174700) at 7p13: mutation in the GLI3 gene (MIM.165240)

Etiology

 Holt-Oram syndrome (atrial and ventricular septal defects, abnormal thumb - from absent to triphalangeal)
 short ribs polydactyly syndromes
 Carpenter syndrome
 trisomy 21
 VACTERL association
 Fanconi syndrome (Fanconi anemia)

See also

 polydactylies

• postaxial polydactyly

References

 Lettice LA, Hill RE. Preaxial polydactyly: a model for defective long-range regulation in congenital abnormalities. Curr Opin Genet Dev. 2005 Jun;15(3):294-300. PMID: #15917205#