Polydactyly

born with an extra finger or toe. These additional digits can range from fully functional to only soft tissue. Polydactyly might present as an isolated condition, known as non-syndromic polydactyly, or as part of a broader syndrome with accompanying physical or intellectual anomalies, known as syndromic polydactyly. There are three main categories of polydactyly: preaxial, central, and postaxial. The most frequent types are postaxial (ulnar) polydactyly (PAP), characterized by an extra digit near the fifth finger or toe, and preaxial (radial) polydactyly (PPD), where the additional digit is near the thumb or big toe. Central polydactyly, which is rarer, is characterized by an extra digit adjacent to the ring, middle or index finger.

Polydactyly is primarily caused by genetic mutations, with some forms inherited through an autosomal dominant pattern and some forms occurring spontaneously (i.e., de novo mutation). Key genes involved include GLI3; sonic hedgehog gene (SHH); fibroblast growth factor (FGF); homeobox protein aristaless-like 4 (ALX4); homeobox D (5’-HoxD); ZNF141; MIPOL1; IQCE; and PITX1. Polydactyly is also thought to result from disrupted programmed cell death, or apoptosis, during fetal limb development. Preaxial polydactyly, specifically, arises from disturbed ectodermal (i.e., the outermost layer of an embryo) and mesodermal (i.e., the middle layer of an embryo) apoptosis early in embryonic development, linked to abnormal gene expression. Additionally, polydactyly may accompany other syndromes including Diamond-Blackfan anemia, Fanconi anemia, Ellis-van Creveld syndrome, VACTERL association, trisomy 13, and trisomy 21.

The primary sign and symptom of polydactyly is the presence of extra fingers, an extra thumb, or extra toes. These additional digits can range from small pieces of soft tissue that have no bones called nubbins to fully formed and functional digits. In some cases, the extra digit may be connected to the side of the hand or foot with only a narrow stalk of tissue.

Polydactyly is typically diagnosed at birth by observing extra digits on the hands or feet. The diagnosis may also be made prenatally through transvaginal ultrasound as early as nine weeks into pregnancy. Typically upon detection, clinicians may conduct further screening tests including ultrasound evaluations of the heart, kidneys, nervous system, and limbs to check for additional anomalies that accompany the associated syndromes. Maternal serum screening, such as testing for alpha fetoprotein (AFP), hCG, estriol, and inhibin A, can further be performed to screen for genetic syndromes that may cause polydactyly. After birth, radiographic examinations are performed to assess the extra digit's bone structure which can help guide treatment planning.

Treatment for polydactyly varies based on the type of polydactyly, the complexity of the case, and whether the extra digit is functional. If the extra digit is non-functional and has no bone, the extra skin can be tied off shortly after birth, which will cause the skin to naturally fall off. More complex cases involving fully formed digits may require surgery to retain the function of the hand or foot and optimize cosmetic appearance. Some may opt to keep the functional extra toe or finger. A treatment team of pediatricians, orthopedic surgeons, and hand specialists is generally involved since the surgeries may involve bones, ligaments, and tendons. Ideally, surgeries are performed around one year of age to minimize developmental impact, and treatment is tailored to individual needs. The prognosis for isolated polydactyly is generally excellent, with most children maintaining full motion in their fingers and toes post-surgery. Referral to a physical therapist or occupational therapist after surgery can help ease the rehabilitation process. If the polydactyly is determined to be linked to a genetic syndrome, further genetic testing and counseling may be advised.

Polydactyly is a birth anomaly where individuals have extra fingers or toes, typically due to genetic mutations. It can appear isolated or as part of a syndrome and is categorized into preaxial, postaxial, and central polydactyly. It is typically diagnosed at birth or through prenatal ultrasound. Treatment varies from tying off simple excess digits to surgical correction for complex cases, often involving specialist consultation. Surgeries are ideally performed by age 1 to minimize developmental impact. Generally, individuals with isolated polydactyly have an excellent prognosis, retaining or achieving full-digit functionality post-treatment.