Related gene: EXTL3
Inheritance pattern: Autosomal recessive
Individuals with this condition can present with severe T cell defects that may mimic severe combined immunodeficiency (SCID) at birth. Additionally, they present with significant bone deformities, such as early fused cranial bones (craniosynostosis) with a small cervical canal, short stature, and abnormally shaped digits. While very rare, all described patients have had neurological complications, including developmental delay. Liver and kidney cysts have been described in several affected individuals. It is inherited in an autosomal recessive pattern. Ig replacement therapy and prophylactic medication against infections are indicated. Many have died early in life, but prolonged survival, with spontaneous improvement of the lymphocyte count, has been reported in others.