The investigatoris will carefully select cartilage-hair hypoplasia patients unexposed to varicella (VZV) and immunize patients in a controlled manner with VZV vaccine. Patients will be selected on the basis of disease severity and the degree of immunodeficiency (including CD4+ T-cell counts). Any potential complication of VZV immunization, such as rash, will be discussed with the patients/caregivers beforehand and acyclovir will be used to treat any VZV related symptoms, consistent with the current practices. The investigators will verify the development of immune response to vaccination by testing for VZV antibodies and cell-mediated immunity.

Inclusion Criteria:

• genetically confirmed cartilage-hair hypoplasia diagnosis
• age >12 months
• no history of chickenpox
• informed concent of the patient/caregiver.

Exclusion Criteria:

• positive serum IgG for varicella zoster virus
• low CD4+ cell counts (<15% or <200 cells/mm3)
• clinical or laboratory signs of severe immunodeficiency
• ongoing intravenous or subcutaneous immunoglobulin treatment