What is Arachnodactyly?

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  • Written By: Emma Lloyd
  • Edited By: C. Wilborn
  • Last Modified Date: 04 November 2019
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Arachnodactyly is a medical condition which causes deformity of the fingers. This condition is also known as achromachia and as spider fingers, because it causes the fingers to grow disproportionately long and slender in comparison to the rest of the hand. Arachnodactyly can be a congenital condition, meaning that a child is born with this finger deformity, or may develop after birth during childhood or adulthood. In the latter case, the disease is referred to as congenital contractural arachnodactyly.

The main symptom of this condition is simply the appearance of the fingers. They are very long and slender, and may also be slightly curved. In some people, the fingers may be unusually flexible, allowing the fingers to be bent backward up to 180 degrees. Arachnodactyly is generally an indication of an underlying disease which is causing the fingers to grow abnormally.

Many people have fingers which are long and slender; this physical characteristic does not always indicate that someone has arachnodactyly. Although this is a normal physical characteristic in most cases, consulting a doctor is still important, particularly if the condition develops during childhood or adulthood. This is because arachnodactyly usually signifies the presence of a more serious medical condition.


There are several distinct conditions which may cause a child to be born with arachnodactyly, or to develop this physical characteristic in the first few years of life. One of these is Marfan syndrome, a genetically-inherited disorder which causes a defect in connective tissue. Children born with Marfan syndrome are usually tall for their age, with long limbs and digits. These children are at risk of developing heart and lung defects.

A related condition called Beals syndrome, Beals-Hecht syndrome, or congenital contractural arachnodactyly, is also a genetic disorder which causes defects in connective tissue. Children with this condition have similar physical characteristics to those with Marfan syndrome, with long, slender digits. In addition, children with Beals syndrome are limited in movement, as their defective connective tissue prevents straightening of many joints, including the fingers and toes, ankles, knees, hips, and elbows.

Children may also develop arachnodactyly if they are born with homocystinuria, or cystathionine beta synthase deficiency. This genetically-inherited condition affects the metabolism of an amino acid called methionine. Children with homocystinuria are unable to metabolize methionine, causing this amino acid to build up to toxic levels. Identifying physical characteristics include long, thin limbs and fingers, knock-knees, high arches, and vision problems. If not diagnosed and treated early, homocystinuria may cause intellectual disability and cardiovascular problems.

The medical conditions that produce arachnodactyly as a symptom tend to be serious in nature. If left untreated, any of the above conditions may cause severe physical or mental harm. For this reason, a child who develops arachnodactyly should be examined by a health care provider to determine the underlying cause of the condition.


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Post 2

This is way off the mark. There is a lot more to this condition than just the appearance of the fingers. It affects the toes, arms and knees. It affects every muscle in the body including the heart. Do some research. I am 62 years old and I was born with it.

Post 1

Is arachnodactyly painful? Do people with this defect have full use of their fingers and hands (not including the other conditions mentioned in the article) or is their use limited? If there is limited use or it's painful what kind of treatment can they be given?

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