Short answers, pulled from the story.
Polydactyly is a birth anomaly that results in the presence of extra fingers or toes. This condition affects the hands more frequently than the feet and can range from a small nubbin of soft tissue to a fully functional independent digit.
Polydactyly occurs within the first four weeks of gestation due to a complex error in limb bud formation. Diagnosis can be made as early as nine weeks via prenatal ultrasound.
At least 39 distinct genetic mutations are linked to polydactyly including mutations in Hoxa or Hoxd clusters and the SHH gene. A cis-acting mutation approximately 1 megabase upstream of the SHH gene creates an ectopic expression zone in preaxial polydactyly.
Medical professionals divide polydactyly into three major types based on the location of the extra digit: ulnar, radial, and central. Ulnar or postaxial polydactyly affects the little finger side while radial or preaxial polydactyly involves the thumb side.
Treatment often involves intricate reconstructive surgery performed around two years of age. Simple ligation may be used for infants with Type B ulnar polydactyly while complex cases require surgical excision or reconstruction.
Henry II the Pious High Duke of Poland had six toes on his left foot and Jiang Qing the fourth wife of Mao Zedong reportedly had six toes on her right foot. Antonio Alfonseca earned the nickname El Pulpo for his extra digits and the Hungarian poet Endre Ady believed his six fingers were a sign of his selection.