Accessory nail of the fifth toe

The trait can be observed on either one or both feet where there is a separation of the toenail on the corner of smallest toe. The smaller sixth toenail separates from the main toenail on the outermost side of the foot, and protrudes outwards from the corner. The additional nail can be cut with a nail clipper.

The cause is poorly understood due to a lack of research, but genome-wide scans indicate that it is a heritable trait, and could be autosomal dominant.^[1] However, the wide variance in the size and structure of the accessory nail indicates that the trait may not follow a Mendelian pattern of inheritance, and may instead be a complex trait affected by multiple genes with minor genetic effects.^[2]

Most people do not seek out treatment because the accessory nail typically does not cause pain or other symptoms that interfere with everyday activities.^[1] For those who do choose treatment, an option is surgical or chemical matricectomy (complete removal or destruction of the nail matrix).^[1][3][4]

Stereotypically endemic to Han Chinese,^[3] it is observed in people from all ethnicities and races.

Chinese mythology has it that during the time of the Yellow Emperor, there were two types of people living in China: those who were the descendants of the Yellow Emperor, and those who were nomadic Qiang people. The Henan people, led by Yin Wang, attacked the Qiang and abducted a Qiang woman, who later tried to escape. Yin Wang stabbed her in the abdomen as she tried to escape, so she gave birth to two children with a scar on the small toe of the foot. The children were taken back by Yin Wang for adoption, and their descendants were born with double nails on their small toes.^[5]

• Congenital malformations of the dermatoglyphs
• Dominance (genetics)
• Epicanthic fold
• List of skin conditions
• Mongolian spot