Dyssegmental dysplasia Silverman-Handmaker type

Overview

Type of disease: Rare conditions

Dyssegmental dysplasia, Silverman-Handmaker type (DDSH) is a rare genetic condition. DDSH is a form of dwarfism that is more severe than its related dyssegmental dysplasia subtype, Rolland-Desbuquois. Babies with DDSH rarely survive to term or beyond a few days of life due to the severe birth defects.

Babies with DDSH do not have normal cartilage. Cartilage is a connective tissue and has many uses in our body because it is more flexible and softer than bone. It helps form joints (like knees and wrists), the ears and nose, parts of the ribs and spinal column (backbone) and the bronchial tubes (the tubes which help us breathe). Common features of DDSH include a flattened face, short neck, bowed arms and legs, abnormal ears, and shorter than normal length. Babies may be born with an opening in the roof of the mouth (cleft palate). Complications include spinal bones of different sizes and shapes, short ribs, and abnormal bones in the arms and legs.

Only about 30 cases of DDSH have been reported in medical literature. Four have been recent enough to confirm that DDSH is caused by changes in the HSPG2 gene. When the HSPG2 gene is not working correctly, not enough perlecan, a protein needed to make cartilage, is made.

DDSH is inherited in an autosomal recessive manner, meaning two copies of the changed (mutated) gene must be present to have DDSH. The parents of the baby are carriers of DDSH and only have one nonworking copy. Carriers do not usually have any symptoms. DDSH may be detected by an ultrasound during the pregnancy or when the baby is born. Genetic testing can confirm the condition.

There is no cure for DDSH and even with extensive medical intervention, babies cannot survive for long. If your baby has been diagnosed with DDSH, talk to your doctor. Additionally, a genetic counselor may be helpful to explain risks to future pregnancies as well as testing options. Support groups are available for more resources and information.

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