Autosomal recessive inherited disorder mainly characterized by short limb short stature, fine, sparse hair, impaired immunity, and anemia. Mapped to RNAase RMRP gene at 9p21-p12. RMRP is a ribonucleoprotein present in the nucleus and mitochondria. RNase RMRP has 2 functions, cleavage of RNA in mitochondrial DNA synthesis and nucleolar cleaving of preribosomal RNA (pre-rRNA). RMRP also plays a role in ribosomal RNA production and may have a role in nuclear DNA replication. RMRP is required for cell growth.
Why it is of interest to PWS:
Skin - hypopigmentation.
Hair - grows slowly and breaks easily, although hair appears normal in some. Hair of scalp, eyebrows, and eyelashes at birth is light in color, fine, sparse, and lacks a central pigmented core, so has a smaller diameter.
Anemia in more than 80%. Although usually mild and self-limited, some (9%) have severe anemia, and in half of these it is permanent.
Head size at birth is within normal reference range, hands are short and pudgy, and skin forms redundant folds around the neck and extremities.
Defective cellular immunity leading to increased susceptibility to infections from opportunistic microorganisms, principally life-threatening varicella (chicken pox) infections and common pathogens observed in T-cell immunodeficiency such as candida species, Pneumocystis carinii, and cytomegalovirus (CMV). In those with more severe impaired cellular immunity, susceptibility to malignancies, especially leukemia and lymphoma, is also increased. Those with predominant B-cell immunodeficiency have increased bacterial sinopulmonary infections.
