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Polydactyly

Dr. Ayush PandeyMBBS,PG Diploma

October 06, 2020

October 06, 2020

Polydactyly
Polydactyly

In 2019, scientists at the University of Freiburg and Imperial College of Science, Technology and Medicine, London, studied a mother (52) and son (17) with six fingers on each hand. The scientists, who published their findings in Nature Communications, wanted to know if these extra fingers served an important purpose or if they were—as per popular belief—vestigial or without a modern-day purpose.

For their study, the researchers gave the mother and son some tasks like folding napkins and tying shoelaces. As a control, they gave the same tasks to people with five fingers. Interestingly, they found that the mother and son could do things like tying shoelaces, texting and playing videogames with one hand compared with five-fingered folk who needed both hands to accomplish these tasks.

From this, the researchers surmised that supernumerary or extra fingers aren’t necessarily vestigial and that the brain and central nervous system are fully capable of adapting to life with an extra digit. Many people who are born with an extra digit have it removed surgically. This research also showed that this surgery may not be required in some cases. And in people who have a fully developed extra digit, it could be quite useful in fact.

The condition of being born with extra fingers and/or toes is called polydactyly. It can be of different kinds, depending on where the supernumerary (extra) digits (fingers/thumbs/toes) are on the hands and/or feet. The different types of polydactyly are ulnar, central and preaxial (more on these later). Read on to know all about polydactyly, types of polydactyly, causes of polydactyly, diagnosis of polydactyly and treatment of polydactyly.

Types of polydactyly

Polydactyly is also called polydactylism, hyperdactyly or hexadactyly. People born with this condition could have extra fingers on one or both hands and/or extra toes on one or both feet. Depending on where the extra digits are located, polydactyly can be:

Extra fingers

  • Preaxial or radial, to the side of or attached to the thumb. This can be further divided into four subtypes, including a triphalangeal thumb (where the thumb has three  phalanges instead of two), triphalangeal digit
  • Mesoaxial or central, with extra digits around the middle three fingers (ring to index); but most often near the index finger
  • Postaxial or ulnar, extra digit at the fifth or little finger. This can be further divided into type A, where the extra little finger is well developed, and type B where it is little more than a bump

Extra toes

  • Tibial, next to the big toe
  • Central, around any of the middle three toes
  • Fibular, next to the little toe

Polydactyly can also be divided based on cause: it can be non-syndromic, meaning there’s no associated syndrome or health condition. Research has shown the involvement of at least six genes in the expression of isolated or non-syndromic polydactyly.

Polydactyly can also be syndromic. Some of the syndromes in which polydactyly is seen are trisomy 13, Bardet-Biedl syndrome and VACTERL (vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, and limb abnormalities).

Polysyndactyly is a combination of syndactyly (fused digits) and polydactyly (extra fingers and/or toes). In this condition, the extra digits are fused with other fingers or toes.

Symptoms of polydactyly

An extra finger or toe is the most prominent symptom of polydactyly. This extra digit could be as small and soft as a bump (nubbin), a finger that broadens to end in two tips or it could be fully developed and functional digit as in the case of the mother and son mentioned earlier in this article.

Polydactyly is more common among boys than girls. It is also seen in hands more commonly than in the feet. According to research, Asians are more likely to have an extra thumb while African Americans are more likely to have an extra little finger.

Causes of polydactyly

Polydactyly is a fairly common congenital anatomical abnormality, in which a person is born with six or more fingers and/or six or more toes. It affects one in 700-1,000 live births.

The condition is hereditary and researchers have identified multiple genes and locations on these genes that are responsible for polydactyly. Polydactyly is an external structural problem that occurs during the “anterior-posterior patterning of developing limb” (the formation of fingers and toes in the womb).

(Congenital anatomical abnormality is a birth defect in which something about the anatomy or body of the child is unusual. Conditions like cup ear, extra nipples, natal teeth and polydactyly are described as minor external congenital abnormalities by the US Centers for Disease Control and Prevention—this is in comparison to congenital problems or birth defetects like spina bifida and congenital heart disease which require urgent and sustained medical interventions.)

While non-syndromic polydactyly is not associated with other conditions, syndromic polydactyly may occur in

  • Trisomy 13: Trisomy 13 is a chromosomal disorder. Where polydactyly is seen with trisomy 13, it is usually postaxial polydactyly (near the little finger).
  • Bardet-Biedl syndrome is often accompanied by postaxial polydactyly in the hands and feet. Researchers have identified 20 genes that are involved in this syndrome.
  • Carpenter syndrome: Children with this syndrome often have acrocephaly or pointed head and cloverleaf skull (severe craniosynostosis, or early fusion of skull bones). The extra digit tends to be next to the little finger or the first/second toe
  • McKusick-Kaufman syndrome: Children with this syndrome have heart defects, genital issues and extra fingers/toes
  • Short rib polydactyly syndrome: Children with this syndrome have a small torso (thorax) as well as extra digits (fingers and/or toes)
  • VACTERL: Polydactyly is one of the possible features of VACTERL or vertebral defects, anal atresia, cardiac defects, tracheo-oesophageal fistula, renal anomalies, and limb abnormalities.

Some other syndromes associated with polydactyly are:

  • Asphyxiating thoracic dysplasia
  • Smith-Lemli-Opitz syndrome
  • Fetal valproate syndrome
  • Hydrolethalus syndrome
  • Joubert syndrome
  • Juberg-Hayward syndrome
  • Lhermitte duclos disease
  • Meckel Gruber syndrome
  • Pallister-Hall syndrome

Polydactyly precautions

Of course, polydactyly is not always to the person’s benefit. In November 2014, Devendra Suthar, a carpenter from Gujarat with seven fingers on each hand and seven toes on each foot, entered the Guinness Book of Records as the person with the most digits in the world. In his interview to Guinness Book, he confessed that while the extra fingers and toes didn’t trouble him, he had to be extra careful while sawing!

While polydactyly does not normally cause problems, if you have an extra digit, it is important to take note of a few things:

  • Keep the digit (and nail) clean. If you also have overlap or fusion in the extra digit, ask your healthcare provider the best way to clean the area and trim the nail.
  • Polydactyly in feet may require special shoes. Remember that wearing tight shoes is a risk factor for infections, corn, bunions and even knee injuries.
  • One more thing that parents should be mindful of is this: if your child is born with an extra finger or toe in either or both hands and feet, you must get it checked by a doctor. In many cases, polydactyly is simply passed down in the family and is nothing to worry about. In case the extra digit is part of a syndrome, getting a checkup will help the doctor diagnose the condition and start treating it early.
  • Different people can have different amounts of strength and flexibility in the extra digit. It might help some children and even grown-ups with extra digits to work with a specialist, to get the maximum use out of the supernumerary finger(s) and/or toe(s).
  • Immediately after polydactyly surgery, it is important to take care of the area and get it properly bandaged by a medical professional to avoid infections and other problems.
  • Those who get polydactyly surgery as children may need follow-up surgery as they grow older. So follow-on visits with a doctor for this would be a good idea.

Diagnosis of polydactyly

Finger buds start appearing in foetuses from the ninth week of pregnancy. While it is possible for specialists to spot some problems at this stage through transvaginal sonography, a clearer picture can emerge in an ultrasound between the 17th week of pregnancy and the 34th week of pregnancy. Whichever stage the doctor detects the problem at, he/she may recommend further tests to check for any anomalies in the heart and for syndromes like trisomy 13, Meckel-Gruber syndrome, Diamond-Blackfan anaemia and Fanconi anaemia.

It is also possible for grown-ups to get gene testing before they plan a pregnancy, to know if they could pass down a polydactyly gene (among other things) to their child. DNA testing can also be done on the foetus, though this isn’t common.

After a child is born, a physical examination can reveal the presence of extra digits. Imaging technologies like X-rays can tell the doctor about the nature of the extra digit. For example, in the mother-son duo studied by the Imperial College researchers, the extra digit didn’t have the usual tendons but more bone in its place.

Polydactyly treatment

In many cases, there’s no treatment necessary for polydactyly. Where treatment is recommended, it is individualised to the patient’s needs as polydactyly can manifest in many different ways in different people.

Where the extra digit is very small or attached by a tiny bit of skin with no involvement of bones or tendons, the doctor may perform an outpatient procedure called suture ligature in which he/she would use a suture or vascular clip to cut off blood supply to the extra digit which would then fall off on its own (autoamputation) in roughly 10-20 days. It is also possible for a trained medical professional to excise or cut the extra digit, depending on the complexity of the extra digit. 

Both suture ligation and excision should only be performed by a trained medical professional, after checking the X-rays to understand the anatomy of the extra digit(s). Doctors also check for “good stability, motion and appearance” in the dominant digit before removing the supernumerary one. A possible side effect of suture ligature for postaxial polydactyly—neuroma formation—can be quite painful.

Where the digit is more developed, with the involvement of tendons, bone and ligaments, surgery may be done to remove the extra digit(s). Such a surgery typically requires reconstruction of many parts of the hand or foot and not just the removal of the extra finger or toe. Some of the reconstruction procedures used are arthroplasty, corrective osteotomy and tendon realignment.

In the case of extra toes, doctors may suggest surgery (where it is needed) before the age of one. This is done to avoid or reduce any impact of the extra digit on the child’s development and walking. Indeed, doctors recommend any surgical intervention for polydactyly be done in early life. That said, people who have such surgery as infants may need follow-up surgery as they grow up.



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