Fanconi anemia is a rare inherited condition that can affect the thumbs. Some people with the condition may be born with extra, missing, or misshapen thumbs.

While Fanconi anemia does not affect the thumbs in every case, a baby born with missing or extra thumbs may require testing for the condition.

Read on to learn more about how Fanconi anemia can affect the thumbs, how doctors diagnose the condition, what treatments may help, and more.

Fanconi anemia does not always affect the thumbs.

According to Boston Children’s Hospital, around 75% of people with the condition will develop certain physical characteristics. These can include any of the following:

  • missing thumbs
  • extra thumbs
  • misshapen thumbs

The individual may also be born with other physical characteristics, such as a missing forearm. They may also have a short stature or low birth weight.

It is important to note that Fanconi anemia is not the only condition that can cause thumb hypoplasia, or missing thumbs. Other conditions that can cause missing thumbs include:

Polydactyly, or extra thumbs or fingers, can develop with no known cause or due to a genetic condition.

This means that, if a baby is born with missing or extra thumbs, it does not automatically mean that they have Fanconi anemia. However, the doctor may still check for the condition, particularly if they have other signs and symptoms or if there is a known family history.

If a baby is born with thumb irregularities, the doctor may test for Fanconi anemia.

They will likely begin by performing a physical examination and taking a full family medical history. They may then order a chromosome breakage test, the main test for Fanconi anemia. This involves testing the blood cells to see if the cells show chromosome breakage.

The doctor may order other tests, such as blood tests and X-rays.

Doctors may recommend surgery if a baby is born with misshapen or extra thumbs. This can include ablation of the thumb, which involves removing the thumb.

If a doctor recommends surgery, they can provide more information about what the treatment involves, as well as at what age they recommend it for the child. Polydactyly surgery may not be suitable until at least the age of 6 to 24 months.

The main symptoms of Fanconi anemia include:

  • frequent infections
  • easy bruising
  • extreme tiredness
  • gum or nose bleeding

Other signs and symptoms that occur in around 75% of cases include:

  • missing or incompletely developed forearm
  • short stature
  • low birth weight
  • light brown birthmarks, known as café au lait spots
  • small head or eyes
  • problems affecting the:
    • kidneys
    • gastrointestinal tract
    • heart
    • central nervous system
    • genitals

While certain signs and symptoms, such as missing or extra thumbs, are apparent from birth, some people do not develop any symptoms until later in life.

Fanconi anemia can cause misshapen, missing, or extra thumbs. These thumb irregularities can occur in about 75% of cases.

Doctors may order a chromosome breakage test to test for Fanconi anemia if a baby is born with missing or extra thumbs. There are other conditions that can cause thumb hypoplasia and polydactyly, so they may order additional tests to confirm the diagnosis and rule out other possible causes.

Surgery can treat extra or misshapen thumbs. A doctor may recommend a procedure such as ablation to remove the extra thumb, which may be suitable from around the age of 6 to 24 months.