Myths of Human Genetics

Marden, P.M., Smith, D.W., and McDonald, M.J. 1964. Congenital anomalies in the newborn infant, including minor variations: a study of 4,412 babies by surface examination for anomalies and buccal smear for sex chromatin. Journal of Pediatrics 64: 357-371.

Camptodactyly

The leaflet is aimed at providing parents and carers with information about a condition called Camptodactyly. Camptodactyly is an abnormal bending of the middle joint of a finger. While it is most common in the little finger, it can be present in other fingers

What causes this condition?

Camptodactyly can be caused by a number of different abnormal structures in your child’s finger:

• tight skin
• contracted tendons and ligaments
• abnormal muscles
• irregularly shaped bones

How common is camptodactyly

Camptodactyly affects about 1 percent of children. It occurs more often in girls than boys.

What are the signs and symptoms of camptodactyly

Camptodactyly means that your child has a bent finger that cannot completely straighten.
It may be present from infancy or start in teenage years, and as the child grows it may become worse

If the case is mild, your child won’t have any symptoms. The finger (probably the little one) will be slightly curved, but it won’t affect hand function in any way. If your child has a more severe case, it could slightly affect their hand function.

There are three types of camptodactyly:

• Type I – infant onset.
• Type II – adolescent onset, more common in girls than boys.
• Type III – associated with other birth conditions.

This leaflet only gives general information. You must always discuss the individual treatment of your child with the appropriate member of staff. Do not rely on this leaflet alone for information about your child’s treatment.

What treatment(s) are available?

• Splinting: The first course of treatment is a programme of stretching and splinting of the finger(s) which is undertaken with the assistance of an Occupational Therapist.
• Physiotherapy and splinting: This works very well with best results gained from early treatment. Treatment starts at Alder Hey and may be continued at a local hospital for further appointments. Treatment will depend on how bent, and how much the finger can be straightened with pressure. The splints will be monitored and adjusted throughout the treatment plan. Often the splints need only be worn during sleep but sometimes splints may need be worn 8-20 hours each day.
• Surgery: If your child’s finger curvature increases rapidly, or if it progresses to the point where it interferes with hand function, your child’s doctor may recommend surgery. Surgery depends upon the abnormality of the finger. Surgery often has limited success and can result in difficulty bending the finger after the operation. There is no single operative procedure recommended for children.

What’s my child’s long-term outlook?

While surgery is usually successful in partially correcting the curvature, your child will likely have some remaining deformity. There is a risk camptodactyly will return and surgery may be needed again in the future.

What are the side effects of my child getting or not getting treatment?

Mild finger flexion abnormalities (bent fingers) rarely cause pain or functional problems with the hand. If your child has a more severe case of camptodactyly it could slightly affect their hand function.

What are the next steps?

The Congenital Hand Service can usually arrange an appointment for assessment and splinting when it is most convenient for you and your child. Patients who may require surgical opinion will need medical review by the Consultant Hand Surgeon.

Does anything increase the risk of someone getting camptodactyly i.e., family history?

Whilst most cases are random, some patients will have a family history of similar bent fingers.

Further information or support?

If you need any further information or advice please contact our Plastic Surgery Specialist Nurse Maria Kelly

This information can be made available in other languages and formats if requested.

Bent little finger: The myth

Some people’s little fingers bend in towards the ring fingers (B), while in other people they are straight (S). The myth is that little fingers can be clearly divided into two categories, bent and straight, and that the trait is controlled by one gene with two alleles, with the allele for B being dominant. Neither part of the myth is true.

The reality

Bent little finger as a character

The technical name for a little finger that bends in towards the ring finger is clinodactyly. When the little finger bends in towards the palm and can’t be straightened out, it is known as streblomicrodactyly, streblodactyly or camptodactyly.

Little fingers range from perfectly straight to bending inwards at a sharp angle. It is not clear whether fingers fall into two discrete categories or there is a continuous range of pinky angle. Hersh et al. (1953) said that bent little fingers bend inward at an angle of 15 to 30 degrees. They found that only 4 out of a sample of 4,304 people had what they considered to be bent little fingers. Marden et al. (1964) identified about 1% of healthy newborns as having bent little fingers.

Family studies

Hersh et al. (1953) identified 51 families in which one or more children had bent little fingers. In 47 of the families, one parent had bent little fingers and the other had straight. Hersh et al. (1953) concluded that bent little finger was caused by a single dominant allele, but the four families in which both parents of a B child were S are inconsistent with this.

Dutta (1965) found two extended families with bent little fingers. Six children of S x S parents were all S, while 22 out of 34 children of B x S parents were B. This fits the model of bent little finger being caused by a single dominant allele, but the number of families is very small. Leung and Kao (2003) found one more extended family in which bent little fingers were common; they concluded that it fit the model of B caused by a dominant allele, but the data also fit a model in which it is recessive.

Conclusion

If only extremely bent little fingers are considered, as done by Hersh et al. (1953), then the bent little finger trait is too rare to be useful for illustrating basic genetics in classrooms. If fingers with a more moderate bend are counted, then there is no clear dividing line between bent and straight, plus no evidence that the trait is genetic. In either case, you should not use bent little finger to demonstrate basic genetics.

References

Dutta, P. 1965. Inheritance of radially curved little finger. Acta Genetica et Statistica Medica 15: 70-76.

Hersh, A.H., F. DeMarinis, and R.M. Stecher. 1953. On the inheritance and development of clinodactyly. American Journal of Human Genetics 5: 257-268.

Leung, A.K.C, and Kao, C.P. 2003. Familial clinodactyly of the fifth finger. Journal of the National Medical Association 95: 1198-1200.

Marden, P.M., Smith, D.W., and McDonald, M.J. 1964. Congenital anomalies in the newborn infant, including minor variations: a study of 4,412 babies by surface examination for anomalies and buccal smear for sex chromatin. Journal of Pediatrics 64: 357-371.

This page was last revised December 8, 2011. Its address is http://udel.edu/~mcdonald/mythbentpinkie.html. It may be cited as pp. 20-21 in: McDonald, J.H. 2011. Myths of Human Genetics. Sparky House Publishing, Baltimore, Maryland.

©2011 by John H. McDonald. You can probably do what you want with this content; see the permissions page for details.