From a spina bifida clinic we have identified two patients with a syndrome of myelomeningocele and Waardenburg syndrome type 3 (WS3). The patients each possess a single, de novo, interstitial deletion of chromosome 2 (2q35-36.2), including the PAX3 gene. Deletion of PAX3 was confirmed by fluorescence in situ hybridization (FISH). Analysis with PAX3 and flanking microsatellites shows that the deleted interval of chromosome 2 is of paternal origin and is at least 2 and 6 cM in the two patients. Interstitial deletions in this region result in the Waardenburg syndrome (WS1), but have not been associated with neural tube defects (NTDs). Although other etiologies have not been formally excluded, these patients raise the possibility of a digenic etiology of their NTDs via a genetic interaction of the deleted PAX3 gene with a second unidentified locus.

An infant with delayed development and multiple congenital anomalies was found to possess a duplication of 14q23 leads to qter. This imbalance arose through segregation of a maternal 14/X translocation, observed in only 28% of the mother's cells. Although the X-chromosome-derived portion of the translocation was late replicating in the proposita, the autosomal segment was not inactivated, leading to functional trisomy for distal 14q. Phenotypic comparison to cases with similar duplications does not allow the clinical description of a partial trisomy syndrome.

The Prader‐Willi Syndrome (PWS) has frequently been associated with chromosomal anomalies involving the region 15q11‐q12. The first case of this syndrome associated with a de novo translocation involving chromosomes 11 and 15 is reported. The breakpoints were identified as 11q25 and 15q11 or q12 [45, XX, t(11;15)(q25;q11–12)], resulting in the deletion of 15pter+ 15q11‐q12. Previously reported cases of PWS associated with translocations are reviewed in relation to the “deletion hypothesis.”

Two members of a large family had a similar multiple congenital anomalies mental retardation (MCA/MR) syndrome and an identical aberration of chromosome 16. Their mothers, who are first cousins, had a different abnormality of one chromosome 16, which appeared to be an acrocentric. We interpret these findings as an insertion of a segment of 16p into 16q. following a three-break rearrangement and meiotic crossing over. The two abnormal children have a duplication of 16p11 leads to p13. The clinical manifestations of these patients differ from those of previously reported cases of dup(16p).

Cytogenetic evaluation of cultured amniotic fluid cells showed mosaicism of three karyotypes: 46,XY; 46,XY [t(13;17)(q13;q25]; and 46, XY [t(11;12)(p11;q13)]. Reanalysis of cells from the four original culture flasks harvested individually revealed that both translocations derived from the same flask. Repeat amniocentesis, as well as peripheral blood obtained postnatally from a phenotypically normal male infant, demonstrated only normal chromosomes (46,XY). This observation represents a case of pseudomosaicism containing two different reciprocal translocations.