Deletion mapping of DNA markers to a region of chromosome 5 that cosegregates with schizophrenia

Abstract

Two independent lines of evidence support the localization of a schizophrenia susceptibility locus to the proximal long arm of chromosome 5. A partial trisomy of chromosome 5 (5q11.2-q13.3) cosegregates with the disorder in a Canadian family of Chinese descent, and DNA markers from proximal 5q cosegregate with schizophrenia (plus related disorders) in families of British and Icelandic descent. We constructed a human:hamster hybrid cell line (HHW 1064) whose only human complement is a chromosome 5 that is missing the trisomic region associated with schizophrenia. In combination with a "matched" cell hybrid (HHW 105) containing an intact chromosome 5, we physically mapped DNA markers relative to the trisomy. "Schizophrenia-linked" DNA markers p105-153Ra (D5S39) and p105-599Ha (D5S76) map within the trisomy and proximal to the 5q11.2 breakpoint, respectively. The hybrid cell lines HHW 105 and HHW 1064 together provide a means to identify and generate syntenic DNA markers to further investigate the location of a schizophrenia locus.

FIG. 1

Trypsin–Giemsa-banded metaphase chromosome preparation from hybrid HHW 1064. The Chinese hamster ovary (CHO) line UCW56 was fused to lymphoblastoid cells from an individual with the chromosomal rearrangement dir ins (46, XX, inv ins)(1;5)(q32.3; q13.3–q11.2). Hybrids that contained a human chromosome 5 under selective pressure (growth at 39°C) were isolated as described previously (4). Metaphase chromosome preparations were stained with trypsin–Giemsa (G-banded), photographed, and then destained and restained by the alkaline–Giemsa (G-11) procedure to unequivocally identify human chromosome 5 (4). The only human chromosome present in HHW 1064, the deleted chromosome 5 del (5) (5pter–5q11.2::5q13.3–5qter), is indicated by an arrow.

FIG. 2

Deletion mapping of chromosome 5 DNA markers to the trisomic region associated with schizophrenia. DNA markers were radiolabeled and hybridized to Southern blots as described previously (6). DNA samples were restriction digested with either HindIII or EcoRI, separated electrophoretically, and transferred to nylon membranes for hybridization. Each blot contained the following lanes of digested DNA: Hu, human lymphoblast DNA: Ha, Chinese hamster ovary DNA: 5, hybrid cell line HHW 105 containing a normal human chromosome 5 (4); 5⁻, hybrid cell line HHW 1064, containing a human chromosome 5 missing 5q11.2–q13.3. Radiolabeled bacteriophage λ DNA digested with EcoRI is the size marker. (A) D5S21 (pJO110HC), HindIII digest; (B) D5S39 (p105-153Ra), HindIII digest.

FIG. 3

Map of the trisomic region. The trisomic region is indicated to the left of chromosome 5. Seven markers mapped within the trisomic region (loci indicated in bold type) and five markers mapped outside the region of chromosome 5. The male recombination fractions for some of the markers are listed to the right. Markers listed within parentheses may be reversed in order, and markers listed in brackets are of unknown genetic order. *Male recombinant fractions as reported in Ref. (8); **male recombinant fraction between D5S78 and D5S71 as reported in Ref. (15).