Achondrogenesis is a group of severe disorders that affect cartilage and bone development. These conditions are characterized by a small body, short limbs, and other skeletal abnormalities. As a result of serious health problems, infants with achondrogenesis usually die before birth, are stillborn, or die soon after birth from respiratory failure. However, some infants have lived for a short time with intensive medical support.
Researchers have described at least three forms of achondrogenesis, designated as type 1A, type 1B, and type 2. The types are distinguished by their signs and symptoms, inheritance pattern, and genetic cause. However, types 1A and 1B are often hard to tell apart without genetic testing.
Achondrogenesis type 1B, also known as the Parenti-Fraccaro type, is characterized by extremely short limbs, a narrow chest, and a prominent, rounded abdomen. The fingers and toes are short and the feet may turn inward and upward (clubfeet). Affected infants frequently have a soft out-pouching around the belly-button (an umbilical hernia) or near the groin (an inguinal hernia).
- Short trunk and limbs
- Narrow chest
- Prominent abdomen
- Protrusion around the belly-button (umbilical hernia), or near the groin (inguinal hernia)
- Short fingers and toes with feet turned inward
- Face may be flat
- Palate may be cleft
- Hydrops fetalis
- Neck is usually short
- Soft tissue of the neck may be abnormally thickened
- Abnormality of bone mineral density
- Anteverted nares
- Aplasia/Hypoplasia of the lungs
- Brachydactyly syndrome
- Frontal bossing
- Long philtrum
- Malar flattening
- Narrow chest
- Short Neck, Nose, Thorax, Stature, Toe
- Skeletal dysplasia
- Thickened nuchal skin fold
Achondrogenesis type 1B is a rare genetic disorder; its incidence is unknown. Achondrogenesis, type 1B is the most severe condition in a spectrum of skeletal disorders caused by mutations in the SLC26A2 gene. This gene provides instructions for making a protein that is essential for the normal development of cartilage and for its conversion to bone. Mutations in the SLC26A2 gene disrupt the structure of developing cartilage, preventing bones from forming properly and resulting in the skeletal problems characteristic of achondrogenesis, type 1B.
Achondrogenesis, type 1B is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder are carriers of one copy of the altered gene but do not show signs and symptoms of the disorder.
Achondrogenesis is diagnosed by physical features, X-ray (radiographic) findings and examination of tissue samples under a microscope (histology). Biochemical tests and molecular genetic tests can be used to confirm the diagnosis.
Prenatal diagnosis of achondrogenesis by ultrasound is possible after 14-15 weeks gestation. Prenatal diagnosis by chorionic villus sampling (10-12 weeks gestation) or amniocentesis (15-18 weeks gestation) is possible if the specific gene mutations have been identified in a family member.
Treatment of achondrogenesis is symptomatic and supportive and involves palliative care, in which physicians attempt to reduce or minimize pain, stress and specific symptoms associated with the disorder. Genetic counseling is recommended for families with an affected child. Psychosocial support for the entire family is essential as well.
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