Identification and Characterization of an Xq26–q27 Duplication in a Family with Spina Bifida and Panhypopituitarism Suggests the Involvement of Two Distinct Genes Frans A. Hol,* ,1 Marga T. Schepens,* Sylvia E. C. van Beersum,* Elena Redolfi ,² Maurizio Affer,² Paolo Vezzoni,² Ben C. J. Hamel,* Pamela S. Karnes,‡ Edwin C. M. Mariman,* and Ileana Zucchi ² * Department of Human Genetics, University Hospital Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands; ² CNR, Istituto di Tecnologie Biomediche Avanzate, Via F.lli Cervi 93, 20090 Segrate MI2, Milan, Italy; and ‡Mayo Clinic, Rochester, Minnesota Received February 1, 2000; accepted July 11, 2000 We investigated a family with a duplication, dup(X)q26 – q27, that was present in two brothers, their mother, and their maternal grandmother. The brothers carrying the duplication displayed spina bi- fida and panhypopituitarism, whereas a third healthy brother inherited the normal X chromosome. Prefer- ential inactivation of the X chromosome containing the duplication was evident in healthy carrier fe- males. We determined the boundaries of the Xq26 – q27 duplication. Via interphase FISH analysis we nar- rowed down each of the two breakpoint regions to 300-kb intervals. The proximal breakpoint is located in Xq26.1 between DXS1114 and HPRT and is con- tained in YAC yWXD599, while the distal breakpoint is located in Xq27.3 between DXS369 and DXS1200 and contained in YAC yWXD758. The duplication com- prises about 13 Mb. Evidence from the literature points to a predisposing gene for spina bifida in Xq27. We hypothesize that the spina bifida in the two broth- ers may be due to interruption of a critical gene in the Xq27 breakpoint region. Several candidate genes were mapped to the Xq27 critical region but none was shown to be disrupted by the duplication event. Re- cently, M. Lagerstro ¨ m-Ferme ´r et al. (1997, Am. J. Hum. Genet. 60, 910 –916) reported on a family with X-linked recessive panhypopituitarism associated with a dupli- cation in Xq26; however, no details were reported on the extent of the duplication. Our study corroborates their hypothesis that X-linked recessive panhypopitu- itarism is likely to be caused by a gene encoding a dosage-sensitive protein involved in pituitary devel- opment. We place the putative gene between DXS1114 and DXS1200, corresponding to the interval defined by the duplication in the present family. © 2000 Academic Press INTRODUCTION Neural tube defects (NTDs) are relatively common birth defects, involving inappropriate formation of the brain or spinal cord, with an average incidence of about 1–2 per 1000 births. Spina bifida and anencephaly are the best-recognized examples of NTDs. The underlying etiology is considered to be multifactorial, meaning that both adverse environmental influences and inher- ited predispositions are implicated. Evidence support- ing the involvement of a genetic component comes from the description of a growing number of NTD genes in the mouse, occasional monogenic human NTD syn- dromes, and familial clustering (Mariman and Hamel, 1992; Harris and Juriloff, 1997; Ross et al., 1998). As yet, very little is known about the genetic factors in- volved in human NTD etiology. The existence of NTD families with an apparent X-linked recessive pattern of inheritance argues for the presence of predisposing genes on the X chromosome (Toriello et al., 1980; Bara- itser and Burn, 1984; Toriello, 1984; Jensson et al., 1988). In fact, several lines of evidence point to Xq27 as the location of one of these genes. Fryns et al. (1996) reported a de novo X/autosomal translocation, t(X;22) (q27;q12.1), associated with lumbosacral spina bifida and myeloschizis, while others reported briefly on a U.S. family in which an Xq26 – q27 duplication is asso- ciated with spina bifida (Goerss et al., 1993). Moreover, this part of the human X chromosome is homologous to an X chromosomal region in the mouse that was re- cently shown to carry a deletion encompassing the Zic3 gene in Bent tail, an established mouse model for X- linked NTD (Klootwijk et al., 2000). X-linked recessive panhypopituitarism (MIM 312000; http://www3.ncbi.nlm.nih.gov/omim/) is a rare but well-defined genetic condition characterized by hy- popituitarism, variable combinations of hypothyroid- ism, delayed pubertal development, and short stature due to growth hormone deficiency (Phelan et al., 1971; 1 To whom correspondence should be addressed. Telephone: +31.24.3614017. Fax: +31.24.3540488. E-mail: f.hol@antrg. azn.nl. Genomics 69, 174 –181 (2000) doi:10.1006/geno.2000.6327, available online at http://www.idealibrary.com on 174 0888-7543/00 $35.00 Copyright © 2000 by Academic Press All rights of reproduction in any form reserved.