OOA (Old Order Amish)

Inheritance: autosomal dominant
Genes: HOXD13

SPD1
Syndactyly type II

Fusion of fingers and toes
Extra toes and fingers
Syndactyly
Polydactyly

Synpolydactyly 1

Clinical Characteristics

General description (for patients):

Fusion and webbing of the 3rd and 4th fingers, and the same for the 4th and 5th toes is commonly seen in this disorder.  Extra fingers and toes are also common but no other skull or bone malformations are associated.  X-rays of the hands and feet may be needed to show the extra digits.  The digit deformities in the hands may cause apparent contractions thereby resulting in the only disability in this disorder, which is slight.  Inheritance occurs directly from one generation to the next (autosomal dominant pattern) with males slightly more frequently affected.

Medical description: 

Many forms of syndactyly occur but usually in association with other cranial or skeletal malformations.  Synpolydactyly 1 is an exception as it involves only the digits.  The 3rd and 4th fingers are encased in a single, webbed cutaneous cover throughout their length, often resulting in limited extension. Likewise, the 4th and 5th toes are webbed.  Within the webs are often partial or complete digits although X-rays may be needed to determine the extent of the polydactyly.  No other systemic malformations are present.

Genetics:

This is an autosomal dominant disorder with a slight excess in males. Occasionally a skipped generation occurs and more severely affected presumptive homozygous individuals have been reported as well.  Evidence suggests that SPD1 is caused by a mutation in the HOXD13 gene on chromosome 2 (2q31-q32).  So far, this condition has been reported only among the Amish of Holmes County, Ohio.

Treatment:

No treatment is necessary. 

Prognosis:

Normal lifespan and function.

Ancillary treatments and support:

Extra wide shoes may be required.

Specialists and speciality centers:

Podiatrist, orthopedist.

References:

Cross, H.E., Lerberg, D.B., and McKusick, V.A.:  Type II syndactyly.  Am . J. Hum. Genet. 20: 368-380, 1968.  PubMed ID: 4298538

Akarsu, A.N., Akhan, O., Sayli, B.S., Sayli, U., Baskaya, G., and Sarfarazi, M.:  A large Turkish kindred with syndactyly type II (syndpolydactyly). 2. Homozygous phenotype?  J. Med. Genet. 32: 435-441, 1995.  PubMed ID: 7666394

Camera, G, Camera, A., Pozzolo, S., Costa, M., and Mantero, R.:  Synpolydactyly (type II syndactyly) with aplasia/hypoplasia of the middle phalanges of the toes: report on a family with eight affected members in four generations.  Am. J. Med. Genet. 55: 244-246, 1995.  PubMed ID: 7717427

Resources:

Synpolydactyly, Geneva Foundation