Because there is an association between polydactyly and several syndromes, children with a congenital upper extremity deformity should be examined by a geneticist for other congenital anomalies. This should also be done if a syndrome is suspected, or if more than two or three generations of the family are affected. Research has shown that the majority of congenital anomalies occur during the 4-week embryologic period of rapid limb development. Polydactyly has been associated with 39 genetic mutations. More specific loci and genetic mechanisms responsible for disorders of duplications will be defined with time, as molecular research continues. Polydactyly can be divided into three major types, which are discussed below. Ulnar or postaxial polydactyly
This is the most common situation, in which the extra digit is on the ulnar side of the hand, thus the side of the little finger. This can also be called postaxial polydactyly. It can manifest itself very subtly, for instance only as a nubbin on the ulnar side of the little finger, or very distinctly, as a fully developed finger. Most commonly, the extra finger is rudimentary, consisting of an end phalanx with a nail, and connected to the hand with a small skin pedicle. Mostly one neurovascular bundle can be identified, with no tendons present in the extra digit. In case of a fully developed extra finger, the duplication usually presents itself at the level of the metacarpophalangeal joint. A triplication of the little finger is very rare. Ulnar polydactyly occurs ten times more often in African populations.
Renpennings syndrome is a neurodevelopmental disorder recognised in males that causes intellectual disability, mild growth retardation with examples in the testes and head, and a somewhat short stature. The condition only affects males, starting at birth. Presentation
People with Renpennings typically begin learning language at an ordinary pace, but by the age of 3–4 they experience a regression in mental and physical development, such as mild low muscle tone resulting in elongated faces and rapid loss in the normal growth of the head (microcephaly). Small testes and short stature are also known to commonly occur. Genetics
It is associated with mutations in the PQBP1 gene. The gene product is a polyglutamine-binding protein involved in transcription and pre-mRNA splicing. The gene itself is located on the short arm of the X chromosome (Xp11.23). The most common mutations causing this condition occur in exon 4. Diagnosis
This diagnosis may be suspected on clinical grounds but should be confirmed by sequencing the PQBP1 gene. Treatment
There is no specific or curative treatment for this condition at present. Management is supportive

Epidemiology
This condition normally only occurs in males but a case in a female has been reported. History
This condition was first characterized in 1962. and later described by Hans Renpenning in 1963 after he documented these traits on many children in one family alone. See also
Lujan-Fryns syndrome
Fragile x syndrome

References


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