Causes And Types Of Dwarfism

Dwarfism is a rare medical condition of short stature that may be caused by a genetic mutation or medical condition affecting bone growth. The condition goes by many names, including 'person of short stature,' 'little person,' and 'LP,' which are preferred over 'dwarf.' Many cases of dwarfism have an unknown cause when a gene spontaneously mutates, but the condition often runs in families.

It's a common misconception that dwarfism is just about height, but the condition comes from a genetic or medical condition. Most individuals with the condition are no more than four feet ten inches tall but short stature can be caused by other medical issues, such as malnutrition, not related to dwarfism. The following are common types and causes of the condition.

Genetics

There are more than two hundred conditions that can cause dwarfism, but the most common types, skeletal dwarfisms in which there is abnormal bone growth, are genetic. Several types of dwarfism are related to genetics such as diastrophic dysplasia and spondyloepiphyseal dysplasias (SED).

Skeletal dysplasia dwarfism is caused by a genetic mutation that is inherited or occurs spontaneously. Some forms of dwarfism are inherited recessively, which means a child must get two copies of the mutated gene to be affected by the condition. Other types can be inherited in a dominant manner, meaning a child needs only one mutated gene from either parent or spontaneously to develop dwarfism.

Growth Hormone Deficiency

Growth hormone deficiency (GHD) is also known as pituitary dwarfism, and it happens when the body does not produce enough growth hormone. In some cases, pituitary dwarfism is associated with other hormonal deficiencies such as vasopressin, which controls water levels; gonadotropins, which control sex hormone production; and thyrotropins, which control thyroid hormone production.

Children who have GHD have an abnormally short stature but normal body proportions. The condition is also characterized by delayed or absent sexual development at puberty. Some individuals develop other symptoms of hormone deficiency such as excessive thirst, headaches, and facial abnormalities. Sometimes the cause of GHD is unknown, but it can be the result of genetic defects, a severe brain injury, or being born with no pituitary gland. For some patients, GHD is present at birth, though it can also be acquired later in life, such as the case with a brain injury.

Achondroplasia

This form of dwarfism known as ACH is a genetic disorder and the most common type of short-limbed dwarfism. The word achondroplasia means 'without cartilage formation,' and it refers to the bone growth that prevents cartilage from changing, especially in the long arm and leg bones. Individuals who have this condition have a torso of normal length but short arms and legs, a prominent forehead, specific facial features, and a large head or macrocephaly.

Achondroplasia can be hereditary, but a spontaneous genetic mutation usually causes it. Most patients with ACH are born to parents of normal height. Someone who has achondroplasia has a fifty percent chance with each pregnancy of having a child with ACH with a partner who does not have the condition. When both parents have achondroplasia, the possibility of having a child with the condition is fifty percent, and the chance of having a child of normal stature is twenty-five percent. When a child inherits the mutation from both parents, the condition is fatal. The disorder affects about one in every fifteen thousand to forty thousand births.

Spondyloepiphyseal Dysplasias

Spondyloepiphyseal dysplasia is an inherited bone growth disorder that causes dwarfism and sometimes hearing and vision problems. The condition is congenital, or present at birth, with short stature, a very short trunk, and shortened limbs although the feet and hands are usually average-sized. This form of dwarfism presents with a normal spinal column length relative to the femur and curvature of the spine that progresses during childhood. There are other skeletal changes characteristic of this type of dwarfism such as flattened vertebrae, a downward or inward-turning foot, and a deformity of the hip joint that causes the upper bones of the leg to turn inward.

Many individuals with spondyloepiphyseal dysplasia have severe nearsightedness and sometimes other vision problems such as detached retinas. About twenty-five percent of patients also have hearing loss. Spondyloepiphyseal dysplasia is inherited in a dominant pattern, which means just one copy of the mutated COL2A1 gene is enough to cause the disorder.

Diastrophic Dysplasia

Also known as diastrophic dwarfism (DTD), diastrophic dysplasia is a congenital condition that affects bone development and cartilage. Individuals with DTD are born with short stature and very short legs and arms. The condition is also characterized by scoliosis, or a progressive spinal curvature and a clubfoot with upward-turning toes. About half of individuals with diastrophic dwarfism are born with a cleft palate, and many have swollen ears at birth that can develop in thickened ears.

Diastrophic dwarfism is a recessively inherited disorder. For a child to have DTD, they must inherit a copy of the mutated gene from each parent. Individuals with diastrophic dwarfism usually have children unaffected by the disorder. About one out of every 100,000 births is affected by diastrophic dwarfism.