Aplasia

What is aplasia?

Aplasia means that something in your body doesn’t develop or work as it should. Many forms of aplasia involve developmental issues present at or before birth. A healthcare provider may notice signs of aplasia, like missing or underdeveloped limbs, in a fetus or newborn. Aplasia may also be diagnosed in childhood or even adulthood if it involves internal tissue like bone marrow.

Aplasia isn’t a single condition. Instead, it’s a medical term to describe any tissue, organ or body part that doesn’t form completely.

How is aplasia different from agenesis, hypoplasia and dysplasia?

Aplasia can be confusing because it’s similar to other medical terms related to developmental problems. Depending on the setting, you may hear these terms used interchangeably:

• Agenesis means that a body part doesn’t form at all. In some medical discussions, aplasia means a basic, primitive organ structure exists. In contrast, agenesis means all parts of an organ are absent.
• Hypoplasia means that a body part is underdeveloped. In some medical discussions, aplasia is a type of in-between development. It involves more development than agenesis (no organ) and less development than hypoplasia (underdeveloped organ).
• Dysplasia means that an organ or body part develops abnormally. Unlike aplasia, dysplasia doesn’t always involve problems with early development where a body part fails to form or starts forming and then stops. Instead, dysplasia usually means abnormal cell or tissue growth. For example, early forms of cancer involve abnormal cell changes called dysplasia that later progress to cancer.

Ask your provider to clarify any confusing terminology so you know what a medical condition means for you or your child.

What are the types of aplasia?

Although all types of aplasia are uncommon, the most well-known diagnoses involve red blood cells, skin, bones and germ cells (sperm and egg). Aplasia can also affect your lung, optic nerve and other organs or body parts.

Pure red cell aplasia (PRCA)

With pure red cell aplasia, your red blood cells don’t develop normally. About every 120 days, your bone marrow makes new red blood cells. During this time, red blood cells mature from their early form, a cell called an erythroblast, into a fully formed red blood cell.

If you have PRCA, your bone marrow may make only a tiny number of erythroblasts or no erythroblasts. As a result, your body doesn’t have enough red blood cells, causing you to have anemia. PRCA is called “pure” because it only affects your red blood cells. Other blood cells — white blood cells and platelets — develop as they should. If all three types of blood cells fail to develop normally, you have a condition called aplastic anemia.

You may be born with PRCA (congenital PRCA), or you can acquire the condition over time. The congenital form of PRCA is called Diamond-Blackfan anemia.

Aplasia cutis congenita

Aplasia cutis congenita involves underdeveloped or missing patches of skin on your infant, especially on their scalp. Sometimes, the tissue and bone underneath their scalp don’t develop entirely either. Skin may also be absent from your infant’s torso, arms or legs.

Aplasia cutis congenita may appear as a hairless part of the scalp with scar tissue underneath. Other times, their underdeveloped skin looks like a thin, hairless membrane.

As the name suggests (“congenita”), it’s a congenital condition, one that’s present from birth.

Radial aplasia

With radial aplasia, the bone in your forearm called your radius doesn’t form. Your forearm contains two long bones, the radius and the ulna. Your ulna extends from your elbow to your wrist, where your pinky finger is located. Your radius extends from your elbow to your wrist, where your thumb is. With radial aplasia, your arm may appear misshapen and bent. Your thumb may be missing or shorter than usual, too.

Radial aplasia is one type of radial ray deficiency, which means a problem related to your radius bone’s development. Radial ray deficiencies range from mild to severe. In some cases, your radius bone forms but is shorter than typical. Other times, your radius doesn’t form at all.

Germ cell aplasia (Sertoli-cell-only syndrome)

Germ cell aplasia involves the absence of germ cells in a person’s testes (testicles). Germ cells are reproductive cells. In people assigned male at birth (AMAB), germ cells eventually become sperm. Without germ cells, it’s impossible to produce sperm, which means that people with germ cell aplasia have infertility.

Germ cell aplasia is also called Sertoli-cell-only syndrome because while germ cells are absent, Sertoli cells are still present in the reproductive system. Sertoli cells normally help germ cells develop into sperm. Without germ cells, though, Sertoli cells don’t have a role to play in sperm production.

Pulmonary aplasia (aplasia of the lung)

Pulmonary aplasia means someone is born with a severely underdeveloped lung. Pulmonary aplasia exists on a spectrum. These problems range from no lung development (agenesis) to mild underdevelopment (hypoplasia).

Pulmonary aplasia exists in-between pulmonary agenesis and pulmonary hypoplasia. With aplasia, a basic lung structure forms, but it’s unable to carry out the work of a fully functioning lung.

Usually, one lung is missing or underdeveloped and the other is normal.

Thymic aplasia

Your thymus is a gland that makes white blood cells called T-cells. T-cells help your body fight infections. With thymic aplasia, your thymus doesn’t form. Being born without a thymus makes you more susceptible to infections.

A missing thymus is a sign of DiGeorge syndrome. DiGeorge syndrome can impact multiple body systems. It can affect the function of your immune system and heart, and it can delay development during childhood.

Optic nerve aplasia

Optic nerve aplasia involves being born without essential parts of one or both eyes, including your optic nerve. Your optic nerve plays a vital role in your vision. It allows your eye to communicate with your brain to process visual information. Thanks to your optic nerve, when your eye sees visual information, like shapes and colors, your brain can translate this information into a visual image that makes sense.

Optic nerve aplasia can cause a range of eye problems, depending on your condition’s severity. Aplasia affecting both eyes can lead to problems with brain development.

How common is aplasia?

Aplasia is rare. The most common types include radial aplasia and pure red cell aplasia, especially the acquired form of PRCA (pure red cell aplasia). Radial aplasia affects approximately 1 out of 30,000 newborns. Radial ray deficiencies (including radial aplasia) are the most common congenital disability involving your arm. The congenital form of PRCA is rare, with an estimated 5 to 7 cases per 1 million births. The acquired form is more common, but we aren’t certain of the exact number of diagnoses.

What causes aplasia?

Most forms of aplasia involve genetic mutations that biological parents pass on to their children. Your genescontain the instructions that determine the type of physical characteristics you’ll have. For example, these instructions determine what organ develops where and how that organ develops. You inherit genes from both biological parents. If there’s a mutation, or an error, in a gene, you may experience developmental issues, like aplasia.

Less often, aplasia appears over time. For instance, acquired PRCA results from other causes and conditions, including infections, autoimmune diseases and some forms of cancer.

In some instances, doctors and scientists don’t know what causes aplasia. These types of aplasia are called idiopathic.

How is aplasia diagnosed?

Some forms of aplasia can be detected during procedures done to follow the progress of a pregnancy, like an ultrasound. Other forms of aplasia are hard to see and are apparent at birth.

With milder forms of aplasia or aplasia related to blood and bone marrow, symptoms may not show up until later in life. Depending on the form of aplasia, you may receive imaging procedures, blood tests, genetic tests, etc., to diagnose your condition.

How is aplasia treated?

Treatment varies depending on your condition. Treatment may include surgery to improve the function of an underdeveloped organ or limb. You may need blood transfusions with severe forms of PRCA. Depending on your condition, you may receive medicine to help with symptom relief or to prevent complications associated with aplasia.

Some forms of aplasia, like germ cell aplasia, can’t be treated.

Is aplasia reversible?

Your outlook depends on your type of aplasia and its causes. For example, acquired PRCA (pure red cell aplasia) may be reversible depending on what’s preventing your body from making red blood cells. Treating the underlying condition interfering with red blood cell production can sometimes cure aplasia.

Aplasia that you’re born with isn’t reversible. In these instances, a healthcare provider may recommend surgery, medication or specialized procedures that can improve the function of a limb or organ, or help you manage symptoms.

A note from Cleveland Clinic

“Aplasia” can mean different things depending on what part of your body is affected, your symptoms, how mild or severe your condition is, etc. Don’t get tripped up by the terminology. If you hear your or your child’s condition described as “aplasia,” “agenesis” or any other related term, ask what these words mean and what to expect over time. Ask a healthcare provider if treatments are available or necessary. If so, discuss what treatment may help. Ask how developmental issues may (or may not) affect everyday life.