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Achondroplasia

Achondroplasia is a hereditary disease, which is based on slowing the growth of bones and cartilage. This causes shorter and abnormally shaped bones, and short stature. “Estimated incidence is at about 1/25,000 live births worldwide” (Bober & Duker, 2013). The age of onset of achondroplasia is prenatal.

The symptoms of this disease vary. Violation of anatomical proportions is noticeable at birth: a child with achondroplasia has a relatively large head, short arms and legs. The forehead is convex. Cerebral part of the skulls is increased. In some cases, there is a possibility of hydrocephalus. There can be a violation of the structure of the facial skeleton, which is caused by abnormal development of bones of the skull base. The eyes of patients with achondroplasia are wide apart and located deep in the orbits. There are extra folds near the inner corners of the eyes. Nose is saddle and flattened with a wide top. Frontal bones protrude noticeably. Upper jaw significantly protrudes forward over the bottom one.

Upper and lower limbs of patients with achondroplasia are uniformly shortened mostly at the expense of the proximal segments (hips and shoulders). Hands of newborn baby reach only the navel. All segments of the limbs are curved. Feet are wide and short. Palms are wide. Fingers II-V are short, almost the same length; I- finger is longer than the others. In the first months of life, there are visible fat pad and skin folds on the extremities. Corpus develops normally. The chest is not changed. The belly is jutting forward, and the pelvis is tilted backwards so buttocks appear stronger than in healthy children.

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Infants with achondroplasia are at higher risk of sudden death during sleep (Trotter & Hall, 2005, p. 777). It is assumed that the cause of death is the compression of the medulla oblongata and the upper part of the spinal cord because of the shape and size of the anomaly foramen. In addition, children with achondroplasia suffer from disordered breathing due to structural features of the face, large tonsils and a small chest.

As children get older, bones become more thicken, bend and lumpy because of the distortion of the epiphyseal bone growth at normal periosteal growth. Because of the increased flexibility of the epiphyseal and metaphyseal cortical bones, valgus and varus deformity of limbs occur. Bending is further aggravated due to excessive traction of well developed muscles and a large mass of normally developing body.

A number of specific strains for achondroplasia rise. Hip bones become bent and twist into the lower divisions. Because of the uneven growth of leg bones, fibula in the upper part extends up and stops articulating with the tibia. Adult patients with achondroplasia suffer from deficient in growth that is caused mainly by shortening the lower extremities. Changes in the head and facial skeleton persist and even become more pronounced. Achondroplasia patients are prone to obesity. Due to the dissolution of the nasal passages, they suffer from otitis media and conductive hearing loss. Due to upper airway obstruction, there can be detected signs of respiratory failure (BSPED, 2011). Frequently, narrowing of the spinal canal is observed. It usually occurs in the lumbar, at least in the cervical or thoracic spine. It can manifest itself by impaired sensitivity, paresthesias and pain in the legs. In severe cases, there may be a violation of the pelvic organs, paresis, and paralysis.

There are two forms of the disease: hereditary and sporadic. Hereditary form involves the transfer of the mutated gene from parents to children. Type of inheritance is autosomal dominant. If both parents have the mutated gene, they will have sick children. Sporadic form means that gene mutation appears occasionally. In this case, heredity is not found. Such mutations can occur under the influence of natural radiation, extreme temperatures, and the formation of chemicals (metabolites that cause mutagenic effect) in the human body.

The cause of this disease is a mutation of the gene FGFR3, which is responsible for the growth of cartilage and ossification (Laederich & Horton, 2010, p. 517). In this case, cartilage growth is inhibited. This results in impaired bone growth in length and its abnormal form. In most cases, the disease is the consequence of a spontaneous mutation (a sudden genetic defect). Factors that contribute to the disease are the presence of the disease in parents, and adult age of parents, especially of father, which contributes to the mutation.

Diagnosis of achondroplasia is based on the following methods: clinical picture, low growth, violation of the proportions of the body that include:

  • Short limbs;
  • Curvature of the legs;
  • Short fingers;
  • Large head and recessed broad nose;
  • X-ray data;
  • Skull that is characterized by violation of the proportions between the front and part of the brain due to the increase of the latter, narrowing of the foramen magnum (the hole through which the brain is connected to the back);
  • Short bones (especially shoulder and hip);
  • Irregular spherical joints;
  • Polymerase chain reaction.

The disease is hereditary, so often symptomatic treatment is used. It consists in using human growth hormone (somatotropin), which slightly increases the rate of bone growth, at least in the first year of life. This hormone is administered continuously in the form of injections each day, preferably before going to bed, to simulate physiological hormone secretion. Surgical treatment is used to correct skeletal deformities. Laminectomy is surgery dissection of the spinal canal, which is carried out in order to relieve pressure on the spinal cord from spinal stenosis (narrowing of the central spinal canal). Osteotomy is surgery that consists in cutting and fixing legs’ bones in the correct anatomical position. It is used in patients with severe curvature of the legs. Also, it is possible significantly increase the length of the limbs.

The most serious complication that can occur is narrowing of the spinal canal with compression of the spinal cord and nerves. This can manifest itself by weakness in the limbs, mobility impairments, decreased sensitivity, violation of the pelvic organs (i.e. incontinence, decreased sexual function in men).

Prevention methods include medical and genetic counseling and prenatal diagnosis that are aimed at detecting fetal abnormalities at the stage of fetal development. From early childhood, achondroplasia patients are treated conservatively complex. Children are appointed with quartz or sun exposure, vitamin B and C, folic acid, fish oil, and a balanced diet. It is important to conduct a general massage and exercise therapy (Trotter & Hall, 2005, p. 780).

The presence of patients in the pedigree is a direct indication for genetic counseling (Trotter & Hall, 2005, p. 772). The geneticist together with specialists of clinical diagnostics specifies the genetic situation in a family, provides a conclusion about the risk of re-birth of a sick child and a need for prenatal diagnosis. In case of detection of a gene in sick parents, it is impossible to prevent the disease as children receive genetic material with the mutated genes that cause the disease.

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