Hand and finger malformations represent a challenging area of clinical genetics from the standpoint of understanding the classification as well as in understanding the genetic etiologies, which are often due to single-gene mutations. The majority of familial types however are not yet associated with specific genes. In addition, there is terrific variation in expression between affected family members.
Another challenge in studying hand anomalies is that the literature will often refer to certain malformation types (e.g., brachydactyly type E) without defining what this type is. If the reader is not familiar with a visual image of the malformation, then learning may be hindered. Accordingly, the purpose of these diagrams is to present images of the common polydactyly, syndactyly, and brachydactly malformations that have been described.
The Hand Syndactylies: Common Types
Polydactylies, Classification for thumb (preaxial) and little finger (postaxial) types.
These diagrams illustrate the main types of polydactyly. These malformations are usually observed in otherwise normal children, and often have an autosomal dominant pattern of inheritance.
Brachydactyly Classification Types
Diagramed below is the classification system used to describe hand anomalies associated with shortening of the fingers. Most are autosomal dominant. For some, genes have been identified but genetic heterogeneity is present in all, as well as variable expression. Darkened areas show the main bone findings. For some types, such as in A5 and B, there is an absence of bones (middle phalanges) so that no “dark” areas are indicated.
Thumb Hypoplasia Classification
These tables and images were adapted from a 2004 paper addressing radial ray digit defects and thumb hypoplasias. See the table below the images for explanation of this classification system.
Explanation of above classification: