Hitchhiker's thumb, also known as ''distal hyperextensibility of the thumb'' is the condition of having a thumb that has a distal phalange that bends backwards in an angle of 90°, it is thought to be inherited in an

autosomal recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...

manner, however, it presents on genetic disorders that are inherited in an

autosomal dominant In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...

manner. This condition is benign (when isolated) and does not cause pain or affect the thumb with the trait negatively. If a person has the genes for this condition, it might present bilaterally, unilaterally, or on none of the thumbs.

Signs and symptoms

Symptoms vary among people with hitchhiker's thumbs, those who have it as an isolated trait aren't affected by any symptoms, however, this trait is sometimes a symptom of other conditions, such as a

hypermobility spectrum disorder Hypermobility spectrum disorder (HSD), related to earlier diagnoses such as hypermobility syndrome (HMS), and joint hypermobility syndrome (JHS) is a heritable connective tissue disorder that affects joints and ligaments. Different forms and sub ...

. The signs of this trait are having a thumb with a distal phalange that is able to bend backwards beyond the normal range of motion. Some people with hitchhiker's thumb also have a Z-shaped deformity, named after the appearance of this deformity, which is that of the letter Z.

Causes

The exact cause of isolated hitchhiker's thumb is not known, it is thought to be inherited in an

manner. However, this trait is often a symptom of an underlying condition, such as *

Diastrophic dysplasia Diastrophic dysplasia is an autosomal recessive dysplasia which affects cartilage and bone development. ("Diastrophism" is a general word referring to a twisting.) Diastrophic dysplasia is due to mutations in the ''SLC26A2'' gene. Affected indivi ...

Hypermobility spectrum disorder Hypermobility spectrum disorder (HSD), related to earlier diagnoses such as hypermobility syndrome (HMS), and joint hypermobility syndrome (JHS) is a heritable connective tissue disorder that affects joints and ligaments. Different forms and sub ...

Rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and hands are involv ...

Diagnosis

The trait does not generally need a medical diagnosis, however, it can help with the diagnosis of an individual who is suspected of having a certain condition.

Treatment

It is not associated with any condition, and does not need treatment.

Incidence

Hitchhiker's thumbs affect 24-36% of the U.S. population.

References