Neural tube defects (NTD) are common findings in the 13q deletion syndrome, but the relationship between the 13q- syndrome and NTDs is poorly understood. We present a child with a 13q deletion and lumbosacral myelomeningocele. This was a boy with microcephaly, telecanthus, minor facial anomalies, and ambiguous genitalia. Cytogenetic and fluorescence in situ hybridization analysis showed a de novo 46,XY,del(13)(q33.2-->qter) with no visible translocation. By using microsatellite markers, the deletion breakpoint was mapped to a 350-kb region between D13S274 and D13S1311 and was paternal in origin. An analysis of 13q deletions with NTDs, including the present case, suggests that a deletion in 13q33-34 is sufficient to cause an NTD. The deletions associated with NTDs are distal to and nonoverlapping with the previously defined critical region in 13q32 for the major malformation syndrome [Brown et al., 1999: Am J Hum Genet 57: 859-866]. Our analysis also suggests that one or more genes in 13q33-34 produces NTDs by haploinsufficiency.

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).

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.

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.