What to know about aplasia

Aplasia is a disorder in which there is no development of an organ, limb, or other body part. Aplasia is obvious at birth in most cases. However, certain types of aplasia may sometimes not be apparent until later in life.

In this article, we look at the causes of various forms of aplasia and their symptoms. We also clarify how it varies, such as hypoplasia, atrophy, agenesis, and dysplasia, from similar conditions.

Types of aplasia

aplasia child
Image credit: Jill Lehmann Photography/Getty Images

There are several forms of this condition, as aplasia can impact any organ or tissue. Some examples include:

Pure Red Cell Aplasia Acquired (PRCA)

Red blood cells begin in the bone marrow as cells that are called erythroblasts. These later develop into mature red blood cells.

People with PRCA do not develop erythroblasts. As a result, they may have aplastic anemia, which is a condition in which the blood cells that the body needs are not created by the bone marrow.

Symptoms of PRCA, according to the National Center for Advancing Translational Sciences, include:

This disorder has different causes, including autoimmune diseases, thymomas, cancers, and viral infections. The origin, however, is unclear in some cases.

Aplasia cutis congenita

Aplasia cutis congenita is a rare disease in which newborns have skin that is missing from parts of their bodies. The underlying structures under the skin, such as the bone, may also not be present in some cases.

The scalp is most often affected by this congenital disorder. However, every part of the body may be affected by it. A thin transparent membrane over the top will be present in the affected areas. It is possible to see the internal organs of the baby through the membrane in certain instances.

Aplasia cutis congenita may be due to a mutation of certain genes.

Radial aplasia

The radius is a bone which connects the humerus bone to the wrist in the upper arm. Without the radius bone, individuals with radial aplasia are born.

The forearm is shorter than it needs to be without the radial bone. In addition, toward the thumb side of the forearm, the hand and wrist turn inward.

Although there are many theorie as to what causes radial aplasia, to ascertain the exact cause of this disease, further study is required.

Germ cell aplasia

Within the testes, the seminiferous tubules are where spermatogenesis, or sperm production, takes place. Two cell types are present in the tubules: spermatogenic cells and Sertoli cells.

Spermatogenic cells aid with the spermatogenesis process. The provision of nutrition to the sperm is one of the main functions of Sertoli cells.

Sertoli cells are present in people with germ cell aplasia but have no spermatogenic cells. This form of aplasia can also be referred to by medical professionals as Sertoli Cell-only syndrome or Del Castillo syndrome.

No physical signs are produced by this form of aplasia. Infertility is the principal indication that a person has aplasia of germ cells.

For this reason, before they try to conceive through penile-vaginal intercourse, a person can not know that they are experiencing this disorder.

If a doctor suspects aplasia of germ cells, a biopsy would usually be conducted using tissue from the person’s studies.

Thymic aplasia

In the immune system, the thymus is a gland that plays an significant role. The thymus allows young T cells to mature and specialize, even though it only functions before puberty.

T cells, such as bacteria , viruses, and cancers, recognize and attack dangerous microbes and cells. However, only one form of microbe or cell is fought off by each T cell.

Alongside DiGeorge syndrome, Thymic aplasia occurs. A small segment of a chromosome is absent in people with this genetic disorder. A baby without a thymus is at high risk of contracting life threatening infections.

Aplasia of the lung

A baby can, in rare cases, be born without one of the lungs.

The review of a baby born without a lung is detailed in a 2015 case report. The study authors note that the baby had breathing problems and needed ventilator treatment shortly after birth.

In an antenatal scan, this type of aplasia can be difficult to recognise. The authors of the case study, however, emphasize that the baby was healthy at the time of writing and met all anticipated growth milestones.

Similar conditions

Agenesis, aplasia, and hypoplasia are very similar concepts that all refer to incomplete development at different stages. They all result in organs or tissues being either incomplete or undersized.

Agenesis

The terms agenesis and aplasia can be used by certain individuals interchangeably.

However, to explain the complete absence of an organ and aplasia, researchers have used agenesis to refer to an organ’s inability to grow beyond the earliest stage.

Hypoplasia

Hypoplasia refers to the underdevelopment of body parts or incomplete development.

In certain cases, aplasia-related disorders can also come under the hypoplasia category. An individual with radial aplasia, for example, does not miss the entire radius bone and instead have a shorter than normal radius bone.

Atrophy

Atrophy is another related term. It refers to the partial or complete wasting of a cell, organ, or tissue following normal, matured growth.

Atrophy typically occurs as a decrease in size or characteristics. It varies from hypoplasia, where the decrease in size is due to the failure of a cell, organ, or tissue to reach normal maturity.

Difference between aplasia and dysplasia

Dysplasia is when cells from tissues or organs grow abnormally, according to the National Cancer Institute. Where the organ or tissue does not grow beyond the earliest stage, it is different from aplasia,

In any part of the body, dysplasia can occur and may affect both children and adults.

Before birth, a doctor may diagnose dysplasia in a developing fetus, and when the child develops, it can trigger developmental issues.

Dysplasia usually refers to the irregular development of tissues or cells in adults. These cells can be precancerous and create tumors if they continue to grow.

There are several forms of dysplasia, and there is still no recognition of the causes of each type.

Sometimes, to describe aplasia or dysplasia that affects a particular area of the body, medical professionals may use the same term.

They may, for example, refer to both radial aplasia and radial dysplasia as the hand of the radial club. Sometimes they can also use this term to refer to radius hypoplasia.

Depending on the particular cause, doctors classify the radial club hand into four distinct forms.

This classification may lead to confusion as to whether the words aplasia and dysplasia are sufficient to be used interchangeably.

However, people should not see the two terms as equivalent. Aplasia and dysplasia are distinct, but they may produce similar results in the same region of the body and cause conditions with a common name.

Summary

Aplasia tends to occur when an organ, limb, or body part does not develop during fetal development.

At birth, several forms of aplasia would be noticeable, but others may not become noticeable until later in life.

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