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Sister chromatid exchanges, which may reflect chromosome repair in response to certain types of DNA damage, provide a means of investigating the increased chromosome fragility characteristic of Fanconi's anemia. By a recently developed technique using 33258 Hoechst and 5-bromodeoxyuridine, it was observed that the baseline frequency of sister chromatid exchanges in phytohemagglutinin-stimulated lymphocytes from four males with Fanconi's anemia differed little from that of normal lymphocytes. However, addition of the bifunctional alkylating agent mitomycin C (0.01 or 0.03 mug/ml) to the Fanconi's anemia cells during culture induces less than half of the increase in exchanges found in identically treated normal lymphocytes. This reduced increment in exchanges in accompanied by a partial suppression of mitosis and a marked increase in chromatid breaks and rearrangements. Many of these events occur at sites of incomplete chromatid interchange. The increase in sister chromatid exchanges induced in Fanconi's anemia lymphocytes by the monofunctional alkylating agent ethylmethane sulfonate (0.25 mg/ml) was slightly less than that in normal cells. Lymphocytes from two sets of parents of the patients with Fanconi's anemia exhibited a normal response to alkylating agents, while dermal fibroblasts from two different patients with Fanconi's anemia reacted to mitomycin C with an increase in chromatid breaks, but a nearly normal increment of sister chromatid exchanges. The results suggest that chromosomal breaks and rearrangements in Fanconi's anemia lymphocytes may result from a defect in a form of repair of DNA damage.

Wilms tumor developed in five cousins in a family. Two with bilateral tumors have died, but three with unilateral lesions have survived. None of the patients had associated chromosome defects, aniridia, hemihypertrophy, or other anomalies. The pattern of Wilms tumor in the family is consistent with several postulated mechanisms of inheritance of the neoplasm, and shows that relatives within affected families may be at risk.

The human enzyme, lysosomal acid phosphatase ACP2, is expressed in nan-rodent somatic cell hybrids as a dimeric molecule. The human-rodent heteropolymer, as well as the human and rodent homopolymer, is associated with lysosomes in these cells. The genes specifying lysosomal acid phosphatase ACP(2) and LDH A are syntenic.

The expression of the adenylate kinase isozymes and of phosphopyruvate hydratase was studied in man-mouse and man-hamster hybrid clones. Concordant segregation of the loci coding for AK-2 and PPH was observed in 54 of 55 primary hybrid clones, and these loci were demonstrated to be synthetic with the loci specifying PGM-1 and PGD. The pattern of expression of the four enzymes in discordant clone suggests the gene order 1pter-(PGD, PPH)-AK-2-PGM-1-centromere. In addition, AK-1 was found to be expressed independently of AK-2.

To test the hypothesis that H-Y antigen (present on both somatic and germ cells in normal males but not normal females) is essential for testicular differentiation, we studied four XX males and three XX true hermaphrodites. Blood cells from six subjects and cultured gonadal fibroblasts from a seventh expressed H-Y antigen. Since expression of this antigen requires the presence of a gene normally carried by the Y chromosome, this gene, and perhaps additional Y chromosomal material, should have been present in the genome of these subjects. In one patient this presence is accounted for by a Y-to-X translocation, detectable by chromosome banding. In another a normal Y chromosome was present in a minor population of cells. In the remaining five, no karyotypic abnormality was detectable. Immunologic detection of H-Y antigen is a sensitive test for the presence of the Y chromosome or of its male-determining segment.

Modifications in the techniques for the induction of mammalian somatic cell hybridization by polyethylene glycol (PEG) have led to procedures that are rapid, simple, and effective. The basic improvements, for both monolayer and suspension fusions, are a short exposure to PEG and a rapid dilution of PEG following treatment. There is a marked effect of PEG concentration on cell hybridization, and there seem to be inherent differences between cells in terms of the extent of cell fusion induced by PEG.

Polymorphisms of the proteins encoded by genes that lie within the major histocompatibility complex (MHC) have served as useful markers for organ transplantation and in genetic analysis of a large number of MHC-linked diseases. To extend the range of MHC polymorphic markers, we used a complementary-DNA probe specific for the fourth component of human complement (C4) to identify a new variant within the MHC. Polymorphic variants at the DNA level were detected among subjects with identical phenotypes of the corresponding protein. C4 genomic polymorphisms are inherited with the segment of the short arm of chromosome 6 that carries the HLA-DR and complement loci. The autosomal codominant mode of inheritance of this genetic marker and its utility for evaluation of 21-hydroxylase-deficiency congenital adrenal hyperplasia, one of the many MHC-linked diseases, were established.

The karyotype and paternal social class were determined for 10,348 consecutively born males. No significant difference in paternal social class was associated with the occurrence of the XYY or the XXY karyotype. This argues against the suggestion that socioeconomic factors significantly affect the frequency of the nondisjunctional events leading to these chromosome abnormalities.

The epidemiological data pertaining to the XYY genotype suggest that there is a three- to fourfold overrepresentation of XYY individuals in mental and penal settings and a twentyfold overrepresentation of mental-penal (special security) settings. The reasons behind the risk for behavioral disability are not known at this time. Tallness and ondulocystic acne are reported frequently to be associated with the genotype. Since much of the available information about the XYY sex chromosome complement is biased, more data is required before definitive statements can be made about the personality characteristics or intelligence of the vast majority of XYY men not appearing in social settings oriented towards behavioral deviancy.

HLA, complement, and glyoxalase I alleles were studied in 29 families in which at least one member has classical 21-hydroxylase-deficiency congenital adrenal hyperplasia. A rare complement allele, C4B*31, was found in over 20% of the haplotypes defined in these families and was always part of the complement haplotype BF*F, C2*C, C4A*Q0, C4B*31 (abbreviated FCO,31). The haplotype containing this rare set of complement alleles always carried the rare HLA allele, HLA-Bw47, usually carried HLA-A3, and almost always had the alleles HLA-Cw6, HLA-DR7, and the glyoxalase I (GLO) allele GLO1. Thus over 20% of the haplotypes in the population studied contained all or almost all of the rare extended haplotype HLA-(A3), Bw47, Cw6,DR7, FCO,31, GLO 1. 3 other haplotypes were each found twice in unrelated patients concordant for their disease phenotype and ethnic background. Extended MHC haplotypes may be markers for different genetic mutations causing 21-hydroxylase deficiency.

A number of patients with retinoblastoma have a deletion of chromosome 13. Comparison of the deleted segments from different individuals reveals that all deletions involve chromosome band 13q14. This observation has lead to the hypothesis that in this region is a gene of genes important in the etiology of retinoblastoma. As a first step toward understanding those genes, the authors successfully isolated five DNA fragments from chromosome 13 using recombinant DNA techniques. The DNA fragments from chromosome 13 will be useful in identifying DNA polymorphic sites that are linked to the retinoblastoma locus tentatively assigned to 13q14. Such DNA polymorphisms will be important in the genetic counselling of families with retinoblastoma. These chromosome 13q14 fragments also may be useful in searching for microdeletions of 13q14.

A young woman with features resembling de Lange syndrome had a normal banded karyotype. Similar phenotypes were present in a maternal aunt and uncle. Utilizing high-resolution banding, the propositus was found to have a chromosomal abnormality characterized by dup(4p)del(9p). Using the same banding technique, her mother and two of her siblings were identified as having balanced reciprocal translocations. Chromosome studies with high-resolution banding should be performed in these instances even in the presence of a normal banded karyotype. Determining a chromosomal basis for the phenotype may lead to a significant reproductive risk in individuals with balanced chromosomal rearrangements and may afford them with the opportunity to pursue prenatal diagnosis.

Anthropometric methods were used to examine 18 males 18 to 69 years old with the Fragile-X syndrome. Thirteen of 15 subjects had macroorchidism. The average height of the individuals with the Fragile-X was less than that of published standards. Seventeen of the 18 subjects had absolute or relative macrocephaly, and two-thirds of the subjects were dolichocephalic. For the group as a whole, facial and ear lengths were increased, and facial breadth, hand length, and foot length were decreased. It is suggested that relationships between various measurements of an individual may be more important than any single measurements for conveying the characteristic appearance of an individual with the Fragile-X syndrome.

A C4 DNA polymorphism that can subdivide C4 allotypes and major histocompatibility complex-linked complement gene cluster allele combinations (complotypes) that are not distinguishable by standard electrophoretic means was used to assess further the distribution and linkage association of C4 variants. Segregation of the DNA polymorphism in family studies allowed assignment of particular variants to particular major histocompatibility complex haplotypes. These studies revealed that some complotypes were exclusively correlated with a particular C4 DNA variant, whereas others were not and could be subdivided according to which particular C4 DNA variant was observed. When complotypes that could be subdivided at the DNA level were considered in relation to flanking major histocompatibility complex markers, it was apparent that complotypes associated with major histocompatibility complex "extended haplotypes" had an exclusive correlation with a particular C4 DNA variant. This finding supports the hypothesis that "extended haplotypes" are unique associations of major histocompatibility complex allele combinations and are genetically similar, stably inherited units.

Chinese hamster X mouse hybrid cells segregating mouse chromosomes have been used to assign a gene for triosephosphate isomerase (TPI-1, EC 5.3.1.1, McKusick No. 19045) to mouse chromosome 6, and a gene for Glyoxalase-I (GLO-1, EC 4.4.1.5, McKusick No 13875) to mouse chromosome 17. The genes for TPI-1 and lactate dehydrogenase B are syntenic in man and probably so in the dog. It is therefore likely that they are syntenic also in the mouse. It is of interest then that there is a mouse gene, Ldr-1, on chromosome 6 that regulates the level of LDH B subunits in mouse erythrocytes. The locus for GLO-1 is closely linked to the major histocompatibility complex in man. Since the major histocompatibility complex in the mouse is present on chromosome 17, this locus and the Glo-1 locus are syntenic in the mouse as well. This finding adds to the number of autosomal gene pairs which are syntenic in both mouse and man and reinforces the belief that there is considerable conservation. of linkage groups during evolution.

Two types of alpha-D-mannosidase isozymes are present in human white blood cells, human diploid fibroblasts, and HeLa cells. One of these (the S isozyme) constitutes the major alpha-D-mannosidase of the human cells, has a pH optimum of 4.4, and is associated with lysosomes. The other (the F isozyme) is most active at pH 6, is acid labile, and is located in the soluble portion of the cytoplasm. The expression of human lysosomal alpha-D-mannosidase was examined in man-hamster hybrid clones, and was found to be concordant with that of phosphohexose isomerase in 54 of 55 primary clones. A locus specifying human lysosomal alpha-D-mannosidase has therfore been assigned to chromosome 19.

The fragile-X syndrome, an X-linked form of mental retardation, is estimated to affect one in every 1,000 to 2,000 live-born male infants. Most commonly, fragile-X syndrome has been detected only after patients clearly demonstrate developmental delay, and frequently detection occurs only if the family history is consistent with X-linked mental retardation. Macro-orchidism is a finding commonly associated with the fragile-X syndrome. It has been suggested that the sparsity of reports of macro-orchidism among prepubertal boys with the fragile-X syndrome might be due to lack of careful measurement of the tests rather than to initiation of the enlargement at puberty. A 5-month-old infant with fragile-X syndrome, ascertained through testicular enlargement noted by actual measurement of testicular size as part of his physical examination, is reported.

Esterase D was quantitatively measured in the red blood cells from three patients from three separate kindreds who had abnormalities of chromosome 13. The esterase D activity was proportional to the number of copies of the q14 region of chromosome 13 present. These findings confirm published data localizing the esterase D gene to chromosome band 13q14, a region which is important in the etiology of retinoblastoma. Fifty-one additional retinoblastoma patients not known to have any chromosomal defect also underwent esterase D determination. In none of these patients did the esterase D measurement detect a 13q14 deletion. The normal esterase D levels in this series of 51 retinoblastoma patients suggest that deletion of an esterase D locus is infrequent in retinoblastoma patients. It must be noted that patients who are mosaics, with a 13q14 deletion in only a fraction of all somatic cells, could possibly have normal red blood cell esterase D levels. Further study is necessary to determine if esterase D determination of all retinoblastoma patients is a worthwhile clinical tool.

BrdU-33258 Hoechst techniques have been used to characterize DNA replication patterns in lymphocytes from hunam females with supernumerary or structurally abnormal X chromosomes. Fluorescence analysis permits identification of late replicating X chromosomes in a very high proportion of cells and affords a high resolution method for determining the interchange points of X-X and X-autosome translocations. Asynchrony among terminal replication patterns of multiple late replicating X chromosomes within an individual cell can occasionally be demonstrated. The arms of isochromosomes usually exhibit symmetrical fluorescence patterns, with replication terminating in bands Xq21 and Xq23 (predominant pattern) or in bands Xq25 and Xq27 (alternative pattern) in both arms. In the vast majority of lymphocytes containing a balanced X-13 or X-19 translocation, the normal X is late replicating. However, DNA synthesis in the translocation products occasionally appears somewhat delayed relative to that expected for an early replicating X, consistent with possible position effects on replication kinetics.