We report on a girl with a de novo monosomy Xpter-->Xp22.3 and trisomy 3pter-->3p23, normal development and stature, mildly affected phenotype, and learning disabilities with a low normal level of intelligence. Late replication studies using BudR demonstrated that the entire der(X) was inactive in 30% of cells. In 62% of cells the inactivation did not spread to the autosomal segment in the der(X). The normal X was inactivated in 8% of cells. Quantitative X-inactivation studies using the human androgen receptor locus assay (HAR) on peripheral leukocytes and buccal epithelial cells showed extreme skewing of methylation (90.4% of the paternal allele). The correlation of cytogenetic and molecular data suggest that the mild phenotype of the proposita is most likely due to preferential inactivation of the entire der(X), which seems to be of paternal origin.

Two rare cases of 6p partial deletion (6p23-rpter) are described. Both patients are at or past the adolescent stage, with severe mental retardation and severe to moderate developmental retardation. Physical dysmorphic features that stand out are: short forehead, borderline microcephaly, low-set malformed ears, hyperplastic nares, dental anomalies and short terminal phalanges. The diversity of the phenotypic features has considerable variations in patients with ring of 6, apparently reflecting the relative loss of p and q arms. A case of a larger terminal deletion and a report of an interstitial deletion is also reviewed.

No abstract