In some fetuses, this process does not occur completely between all fingers or toes and some residual webbing remains. Genetics
Five types of syndactyly have been identified in humans. The corresponding loci associated with these types and their common phenotypical expression are as follows:

type I:  2q34-q36; webbing occurs between middle and ring fingers and/or second and third toes. type II:  2q31; also involves long and ring fingers, but has a sixth finger merged in between. type III:  6q21-q23; small finger is merged into the ring finger. type IV:  7q36; involves all fingers and/or toes. type V:  2q31-q32; similar to type I, but the metacarpals and metatarsals may also be fused. Management
Syndactyly of the border digits (thumb/index finger or ring/small fingers) is treated at early age to prevent the larger digit from curving towards the smaller digit with growth. Typically, syndactyly of these digits is treated at six months of age. The treatment of syndactyly of the other digits is elective and is more commonly performed when the digits have grown, at 18–24 months of age. Techniques
Because the circumference of the conjoined fingers is smaller than the circumference of the two separated fingers, there is not enough skin to cover both digits once they are separated at the time of surgery. Therefore, the surgeon must bring new skin into the area at the time of surgery. This is most commonly done with a skin graft (from groin or anterior elbow).
Genotype I has been divided into five subclades, A through E.In late 2016, a large outbreak began in Minas Gerais state of Brazil that was characterized as a sylvan or jungle epizootic. It began as an outbreak in brown howler monkeys, which serve as a sentinel species for yellow fever, that then spread to men working in the jungle. No cases had been transmitted between humans by the A. aegypti mosquito, which can sustain urban outbreaks that can spread rapidly. In April 2017, the sylvan outbreak continued moving toward the Brazilian coast, where most people were unvaccinated. By the end of May the outbreak appeared to be declining after more than 3,000 suspected cases, 758 confirmed and 264 deaths confirmed to be yellow fever. The Health Ministry launched a vaccination campaign and was concerned about spread during the Carnival season in February and March. The CDC issued a Level 2 alert (practice enhanced precautions. )A Bayesian analysis of genotypes I and II has shown that genotype I accounts for virtually all the current infections in Brazil, Colombia, Venezuela, and Trinidad and Tobago, while genotype II accounted for all cases in Peru. Genotype I originated in the northern Brazilian region around 1908 (95% highest posterior density interval [HPD]: 1870–1936). Genotype II originated in Peru in 1920 (95% HPD: 1867–1958). The estimated rate of mutation for both genotypes was about 5 × 10−4 substitutions/site/year, similar to that of other RNA viruses.