Achondrogenesis type 2

December 31, 2014

Synonyms

Overview

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.

Infants with achondrogenesis type 2, which is sometimes called the Langer-Saldino type, have short arms and legs, a narrow chest with short ribs, and underdeveloped lungs. This condition is also associated with a lack of ossification in the spine and pelvis. Distinctive facial features include a prominent forehead, a small chin, and, in some cases, an opening in the roof of the mouth (a cleft palate). The abdomen is enlarged, and affected infants often have a condition called hydrops fetalis, in which excess fluid builds up in the body before birth.

Symptoms

Narrow chest
Abnormally small or short bones in the arms and/or legs
Thin ribs
Underdeveloped lungs
Small chin and cleft palate
Bone formation is abnormal in the spine and pelvis
Abnormal accumulation of fluid may occur (hydrops fetalis)
Abdomen may be enlarged
Abnormality of bone mineral density
Anteverted nares
Aplasia/Hypoplasia of the lungs
Frontal bossing
Hydrops fetalis
Long philtrum
Macrocephaly
Malar flattening
Micromelia
Narrow chest
Short Neck, Nose, Stature, Thorax
Skeletal dysplasia
Thickened nuchal skin fold

Causes

Three forms of achondrogenesis, type 1A, type 1B and type 2, are distinguished by signs and symptoms, pattern of inheritance, and the results of imaging studies such as x-rays (radiology), tissue analysis (histology), and genetic testing.

Type 2 achondrogenesis is inherited in an autosomal dominant pattern and is caused by new (de novo) mutations in the COL2A1 gene.

This is an autosomal dominant disorder because only one copy of the altered gene is necessary to cause the condition. The disorder is not passed on to the next generation, however, because affected individuals do not live long enough to have children.

Diagnosis

Ultrasound examination at 12 weeks gestation revealed severe generalised subcutaneous oedema in a pregnancy at risk for achondrogenesis type II. Transvaginal scanning confirmed the oedema and suggested abnormal limb development. The prenatal diagnosis was confirmed by X-ray examination after transvaginal termination.

Prognosis

This disorder is fatal at birth or soon after. Type 1 is considered more severe, partly because infants with type 1 are more likely to be stillborn and generally succumb to the disorder earlier than infants with type 2 achondrogenesis.

Treatment

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.