An extra digit: Not a sign of good or evil, but an autosomal dominant trait!

By Shilpa Nangali

In childhood days, we heard stories of popular superstition that extra digits in a hand are a sign of great good or evil. It is said that an extra finger on the right hand is supposed to bring good luck, ill-fortune if on the left. Six fingers on both hands indicate that its possessor will be famous or infamous in some way, like Gath, the Philistine giant mentioned in the Bible. Polydactyly reminds me of Antonio Alfonseca, a Major League Baseball pitcher, who has an extra digit on each hand and foot. Hrithik Roshan, an award-winning Bollywood actor is also born with a supernumerary thumb on his right hand. However, an extra thumb on his right hand doesn’t bother me when he has so much talent on the other side. Most people think it brings good luck. I believe that no one is born lucky; luck is what happens when preparation meets opportunity. And, it solely depends on us how we create opportunities for ourselves!

Moving away from superstitions and blind beliefs about polydactyly, let’s now know about the genetics of this condition. Poldactyly, which is a congenital abnormality, is the presence of more than the normal number of fingers or toes. This condition is usually inherited as an autosomal dominant characteristic and can usually be corrected by surgery. If recommended, the surgery is usually done while the child is about 1 year of age. These extra digits are sometimes called supernumerary, in a reference to the fact that they exceed the number of conventional digits. Polydactyly is not life threatening or harmful, although it may be associated with a more serious genetic condition which does require treatment. In some parts of the world, people choose to remove these excess digits to avoid comment or social isolation.

These extra digits can take a number of different forms. The most common is a stub of tissue without any joints, typically located next to the little finger or toe. In some cases, however, the extra digit has bones and articulated joints, and it can even be used. This can cause x-rays to look quite unusual and sometimes a bit confusing. Some people have polydactyl thumbs, meaning that they have two thumbs on the same hand, typically right next to each other.

Usually, African Americans, more than other ethnic groups, can inherit a sixth finger. Extra digits may be poorly developed and attached by a small stalk (generally on the little finger side of the hand). Or, they may be well-formed and may even function. Poorly formed digits are usually removed. Simply tying a tight string around the stalk can cause it to fall off in time if there are no bones in the digit. Larger digits may need surgery to be removed. The doctor should ask the parents whether there was polydactyly at birth, because a person may not know they have it.

Causes and symptoms: Polydactyly is due to errors in the process of fetal development. There will be an error in the genes which determine the shape of the hand or foot. Most often these errors are due to genetic defects. Polydactyly occurs in the womb as a detour on the road to developing just one thumb and four fingers on the hand. In the womb, the new hand starts out in the shape of a paddle, then splits into separate fingers. Sometimes the fingers do not split apart enough, and webbed fingers result, which is called as ‘syndactyly’. Sometimes a extra split forms and extra fingers resulting in polydactyly. Polydactyly can occur by itself as an isolated condition or in conjunction with other symptoms as one aspect of a multi-symptom disease. There are several forms of isolated polydactyly, which is caused by an autosomal dominant gene. This means that since the gene is autosomal (not sex-linked), males and females are equally likely to inherit the trait. Since the gene is dominant, children who have only one parent with the trait have a 50 percent chance of inheriting it. However, people in the same family carrying the same gene can have different degrees of polydactyly. In other instances, the condition may be part of a larger genetic condition such as aneuploidy, an odd number of chromosomes which can lead to serious birth defects.

Polydactyly is also possible outcome of a large number of rare inherited and developmental disorders. This can be present in more than 100 different disorders where it is a minor feature compared to other characteristics of these diseases. In some isolated cases of polydactyly, it is not possible to determine the cause. Some of these cases might nevertheless be due to genetic defects; sometimes there is too little information to demonstrate a genetic cause. Some cases might be due external factors like exposure to toxins or womb anomalies.

Also, if a person is suffering from any of the following disease/syndrome, then he/she can have polydactyly.

• Asphyxiating thoracic dystrophy
• Carpenter syndrome
• Ellis-van Creveld syndrome (chondroectodermal dysplasia)
• Familial polydactyly
• Laurence-Moon-Biedl syndrome
• Rubinstein-Taybi syndrome
• Smith-Lemli-Opitz syndrome
• Trisomy 13

Types: Polydactyly is one of the most common variations on the basic growth pattern of the hand. There are several forms of polydactyly, ranging from a small extra bump on the side of the hand, a finger which widens to end in two fingertips, an extra finger which dangles by a thin cord from the hand, a hand which looks normal except that it has a thumb and five fingers, and an infinite number of other variations. Usually, when a digit has duplicated, each half is somewhat smaller than usual, and it is common for the joints to angle to the sides, often in mirror image zig zag directions.

The following are the types of polydactyly:

(1) Polydactyly with cleft lip/palate and psycho motor retardation (Varadi-Papp Syndrome)
(2) Polydactyly tiopia syndrome
(3)Polydactyly post axial dental and vertebral
(4)Polydactyly post axial with median cleft of upper lip
(5)Polydactyly post axial
(6)Polydactyly preaxial type 1
(7)Polydactyly syndrome middle ray duplication
(8)Polydactyly visceral anomalies cleft lip palate

Prognosis: The prognosis for isolated polydactyly is excellent. When polydactyly is part of a syndrome or group of medical conditions, the prognosis depends on the syndrome. Some of these syndromes can be quite serious.

Diagnosis: Polydactyly and syndactyly can be diagnosed by external observation, X-ray, fetal sonogram, chromosome studies, enzyme tests or metabolic studies. During pregnancy, this condition may be diagnosed with ultrasound or a more advanced test called embryofetoscopy during the first three months (trimester).

Treatment: Polydactyly can be corrected by surgical removal of the extra digit or partial digit. The only treatment for polydactyly is surgery. Since the condition is not harmful, most surgery is cosmetic, although in some cases the extra digits may interfere with normal life. Some people choose to retain their polydactyly, and other than trouble finding gloves that fit, the condition is usually not an issue. However, in some areas birth defects are treated with serious superstition; deformities are treated as curses and they are associated with Satan and evil doings. In these cases, surgery is a good choice, because it will allow the patient a much happier life. Surgery for polydactyly is usually best done in the first few years of life so that the look, feel and function of the corrected hand is the most natural for the child. A hand therapist can help with some problems before and after surgery, tailored to the individual problem and the temperament of the child, but some children proceed through their surgery and recovery without needing therapy.

One should not forget that proper home care is also needed after surgery. For example, you will need to check the surgical area to make sure that it is healing correctly and to change the dressing.

I have read in few research articles that the surgery for polydactyly is sometimes fairly complicated, as there may be variations in all of the structures of the digit which is kept - twisted bones, crooked joints, missing or extra tendons, nerves, and blood vessels. Abnormalities in the fingers which are kept may be more obvious after surgery than before, but with careful planning, a hand surgery specialist will attempt to anticipate and correct these problems at the time of surgery. After surgery, it is usual to protect the hand in a large bandage for weeks to months, depending on what is done. Surgery done in childhood may need to be adjusted for growth with "touch up" surgery when the child is older.

Success of the treatment: The goals of surgery are to improve the appearance of the hand and to prevent progressive deformity from developing as the child grows. Surgery is generally successful in both of these areas, largely correcting the appearance and social stigmata of congenitalism. In many cases, surgery results in a greatly improved but not perfectly normal appearance, and in some situations a normal appearance can not be expected. For example, each of the duplicated thumbs in the above diagram is likely to be smaller than a normal thumb, and no amount of surgery will allow a smaller thumb to "catch up" and perfectly match a normal size thumb on the opposite hand.

I think generally what people notice about another person's hand is not the appearance of an individual finger or thumb, but the way a person uses his hand. Hiding one's hand actually draws attention to it, and if surgery allows the person to use their hand in a natural, unselfconscious way, many small details, such as a somewhat small thumb, will go unnoticed. People are less likely to be satisfied with surgery for polydactyly if surgery is delayed past early childhood.

Sources: WiseGeek.com, Wikipedia.org, NLM.NIH.gov, ChildrensHospital.org, HMC.PSU.edu, AccessExcellence.org, Eatonhand.com, UMM.edu, Healthatoz.com, WrongDiagnosis.com, BBC.co.uk, SkinAtlas.com, Britannica.com, Healthcentral.com, Bhejacry.com, UNP.co.in, BWTorrents.com, Answers.com and Unexplained-mysteries.com.