Pentasomy X: report of patient and studies of X-inactivation.

A five-year-old girl presented with mental retardation (MR), microcephaly, short stature, ptosis, malocclusion, abnormal elbows, fifth finger clinodactyly, joint hyperextensibility in hands and feet, renal hypoplasia, nonobstructive ureteral stasis, pyelonephritis, and renal failure. Five X chromosomes (49,XXXXX) were found in all peripheral blood lymphocytes and skin fibroblasts examined. Xa RBC typing, utilizing serial dilutions of antiserum, gave agglutination at a higher titer than in either Xg(a+) positive parent; the patient's serum IgM was also elevated. These immunological findings imply a lack of dosage compensation and incomplete inactivation of some X-linked loci.