Gender verification in competitive sports

The possibility that men might masquerade as women and be unfair competitors in women's sports is accepted as outrageous by athletes and the public alike. Since the 1930s, media reports have fuelled claims that individuals who once competed as female athletes subsequently appeared to be men. In most of these cases there was probably ambiguity of the external genitalia, possibly as a result of male pseudohermaphroditism. Nonetheless, beginning at the Rome Olympic Games in 1960, the International Amateur Athletics Federation (IAAF) began establishing rules of eligibility for women athletes. Initially, physical examination was used as a method for gender verification, but this plan was widely resented. Thus, sex chromatin testing (buccal smear) was introduced at the Mexico City Olympic Games in 1968. The principle was that genetic females (46,XX) show a single X-chromatic mass, whereas males (46,XY) do not. Unfortunately, sex chromatin analysis fell out of common diagnostic use by geneticists shortly after the International Olympic Committee (IOC) began its implementation for gender verification. The lack of laboratories routinely performing the test aggravated the problem of errors in interpretation by inexperienced workers, yielding false-positive and false-negative results. However, an even greater problem is that there exist phenotypic females with male sex chromatin patterns (e.g. androgen insensitivity, XY gonadal dysgenesis). These individuals have no athletic advantage as a result of their congenital abnormality and reasonably should not be excluded from competition. That is, only the chromosomal (genetic) sex is analysed by sex chromatin testing, not the anatomical or psychosocial status. For all the above reasons sex chromatin testing unfairly excludes many athletes. Although the IOC offered follow-up physical examinations that could have restored eligibility for those 'failing' sex chromatin tests, most affected athletes seemed to prefer to 'retire'. All these problems remain with the current laboratory based gender verification test, polymerase chain reaction based testing of the SRY gene, the main candidate for male sex determination. Thus, this 'advance' in fact still fails to address the fundamental inequities of laboratory based gender verification tests. The IAAF considered the issue in 1991 and 1992, and concluded that gender verification testing was not needed. This was thought to be especially true because of the current use of urine testing to exclude doping: voiding is observed by an official in order to verify that a sample from a given athlete has actually come from his or her urethra. That males could masquerade as females in these circumstances seems extraordinarily unlikely. Screening for gender is no longer undertaken at IAAF competitions.

Genetic mapping of the erythropoietin receptor gene

We describe a novel, highly informative (polymorphism information content, PIC, = 0.86) simple sequence repeat polymorphism at the 5' end of the gene encoding the human erythropoietin receptor (EPOR) previously assigned to 19p13.2 by in situ hybridization. Fourteen different allelic size variants were identified in 12 families of the CEPH (Centre d'Etude du Polymorphisme Humain) family panel of 40 families. In pairwise linkage 16 of the 65 chromosome 19 markers reported to the CEPH database gave a lod score exceeding 3.0 when tested against EPOR. The most likely location of EPOR within a framework of 10 markers including orientation and information on reported physical assignments was pter-[INSR-D19S177-D19S176]-D19S24-LDLR-++ +EPOR-cen-D19S7-D19S49-D19S75-D19S47-AP OC2-qter, placing EPOR as the most proximal of the tested loci on the short arm. On an 11-point map the position and order for all other loci except INSR were supported by the data with odds exceeding 1,000:1. The polymorphism at the 5' end of EPOR should provide a useful landmark marker for future mapping studies of this region.

Localization of the EPM1 gene for progressive myoclonus epilepsy on chromosome 21: linkage disequilibrium allows high resolution mapping

The gene for Progressive myoclonus epilepsy of Unverricht-Lundborg type (EPM1) has previously been mapped by linkage to markers on chromosome 21q22.3. By analyzing crossover events in multiplex disease families with newly detected markers from the region we were able to narrow the localization of EPM1 to an interval of approximately 7 cM, between loci D21S212 and CD18. To further refine the localization of the EPM1 gene we applied linkage disequilibrium mapping in 38 Finnish families, consisting of 12 with multiple affected children and 26 with a single affected child. Based on existing knowledge about the structure and history of the isolated Finnish population, we estimated genetic distances based on strong linkage disequilibrium to several marker loci and found that EPM1 resides within 0.3 cM or less of loci PFKL, D21S25 and D21S154. As this genetic distance translates into a likely physical distance of 300 kb or less, these data provide a basis for highly focused attempts to clone EPM1.

Haplotype analysis to determine the position of a mutation among closely linked DNA markers

Positional cloning involves first finding linkage between an inherited phenotype (such as a disease) and a DNA marker, followed by the use of a variety of physical and genetic mapping techniques to move from linkage to mutation. If there is a founder effect within a population, crossovers are often rare between the mutation causing the phenotype and closely situated markers and increasing disequilibrium may be observed as the site of the mutation is approached. Standard coefficients of disequilibrium may, however, be insensitive to the relative position of close markers and the mutation, because they depend upon allele frequencies in the normal population compared to those of the founder chromosome. Using cystic fibrosis in European populations as a model system, alternative methods for determining the position of a mutation are discussed. These include haplotype parsimony and three-way interval likelihood analysis. Both methods predict the location of the major CF mutation accurately from a real set of more than 600 European CF chromosomes.

Characterization and sequencing of the sex determining region Y gene (Sry) in Akodon (Cricetidae) species with sex reversed females

The sex determining region Y gene (Sry) is the strongest candidate to be the testis determining factor gene (Tdy). Several South-American Akodon species have two varieties of Y chromosome. One type transmitted via male specimens induces testis development. The second Y variety fails to induce male gonadal differentiation and gives rise to fully fertile XY females. These variant females test positive for Sry. Moreover, sequencing of a partial open reading frame of the conserved region of Sry from males and XY females shows no sequence difference. Sry is two- to sixfold amplified in six of eight akodont species tested. Since Sry amplification was found in species having and not having XY females, amplification apparently does not in itself play a primary role in the origin of sex reversal. The development of fully fertile ovaries in XY Akodon females is not due to a deletion of Sry or to mutations in the Sry segment analyzed in this report. Sex reversal may be due to abnormal expression of this gene at the stage of gonadal differentiation. Alternatively, other genes in the sex-determining pathway may be involved. Several of the Akodon species showing Sry amplification also have amplification of Zfy, which may map to the same region of the Akodon Y chromosome.

Truncated erythropoietin receptor causes dominantly inherited benign human erythrocytosis

Erythropoietin regulates the proliferation and differentiation of erythroid precursor cells. Its effect is mediated by the erythropoietin receptor (EPOR), a member of a large family of cytokine receptors. The EPOR gene has recently been cloned, sequenced, and characterized. As shown experimentally, its intracellular C-terminal part contains a domain exerting negative control on erythropoiesis. Here we describe a G to A transition in nucleotide 6002 of the EPOR gene that converts a TGG codon for tryptophan into a TAG stop codon, predicting the truncation of the 70 C-terminal amino acids of the EPOR molecule. The mutation occurs in heterozygous form in the germ-line DNA of members of a large kindred in which primary erythrocytosis is segregating as a mild autosomal dominant trait. The mutation cosegregates with the disease phenotype in all 29 affected family members studied; it occurs in no unaffected family members or unrelated controls. This appears to be an example of a human condition caused by an EPOR mutation. Striking similarities exist between the human phenotype described here and phenotypes of cell lines expressing similarly truncated EPOR molecules produced experimentally. By analogy with these in vitro studies, one can hypothesize that the truncated EPOR molecules are activated by suppression of phosphorylation leading to loss of the down-modulation exerted by intact EPOR molecules. Experimental modifications of the EPOR gene may eventually have therapeutic applications.

Anhidrotic ectodermal dysplasia gene region cloned in yeast artificial chromosomes

Anhidrotic ectodermal dysplasia (EDA), an X-chromosomal recessive disorder, is expressed in a few females with chromosomal translocations involving bands Xq12-q13. Using available DNA markers from the region and somatic cell hybrids we mapped the X-chromosomal breakpoints in two such translocations. The breakpoints were further mapped within a yeast artificial chromosome contig constructed by chromosome walking techniques. Genomic DNA markers that map between the two translocation breakpoints were recovered representing putative portions of the EDA gene.

Cartilage-hair hypoplasia gene assigned to chromosome 9 by linkage analysis

Cartilage-hair hypoplasia (CHH) is an autosomal recessive skeletal dysplasia of unknown pathogenesis leading to short-limbed stature. Associated features include hypoplasia of hair, abnormal cellular immunity, deficient erythrogenesis, increased risk of malignancies, Hirschsprung disease, and Diamond-Blackfan type hypoplastic anaemia. We mapped the CHH gene by linkage analysis with 5 markers to chromosome 9. Multipoint linkage analysis gives a lod score of 9.94 for a location between D9S43 and D9S50. Based on strong linkage disequilibrium the closest marker, D9S50, is likely to be less than 1 cM from the gene. No heterogeneity was observed in 14 Finnish families, nor was there evidence of reduced penetrance. These results provide a starting point for the eventual cloning and characterization of the CHH gene.

Prenatal diagnosis of diastrophic dysplasia with polymorphic DNA markers

Ultrasonography is a non-invasive method for prenatal detection of diastrophic dysplasia (DTD) in the second trimester of pregnancy. As there is a need for genetic counselling as early as possible we wished to develop a method based on molecular analysis. Five fetuses in families with a previous history of DTD were studied by typing them and their relevant family members for DNA markers closely linked to the DTD gene. The DNA analyses predicted that three of the fetuses were unaffected and two affected. These results were concordant with those obtained by ultrasonography, and the phenotype of the fetus was correctly predicted in all cases. DNA analysis provides a reliable means of prenatal diagnosis in the first trimester of pregnancy.

Familial erythrocytosis genetically linked to erythropoietin receptor gene

Familial erythrocytosis is heterogeneous with diverse causes. Using a highly informative, simple sequence repeat polymorphism in the 5' region of the erythropoietin receptor gene (EPOR), we did linkage analysis in a large family whose clinical and genealogical features were known. There were no recombinations between the disease phenotype and the polymorphism, the logarithm of odds score for linkage at zero recombination being 6.37. This highly significant linkage indicates that a mutation in EPOR is most probably responsible for the disease phenotype in this family.

Mapping of the regulatory subunits RI beta and RII beta of cAMP-dependent protein kinase genes on human chromosome 7

The genes encoding the regulatory subunits RI beta (locus PRKAR1B) and RII beta (locus PRKAR2B) of human cAMP-dependent protein kinase have been mapped in the basic CEPH (Centre d'Etude du Polymorphisme Humain) family panel of 40 families to chromosome 7p and 7q, respectively, using the enzymes HindIII and BanII recognizing the corresponding restriction fragment length polymorphisms (RFLPs). Previous data from the CEPH database and our present RFLP data were used to construct a six-point local framework map including PRKAR1B and a seven-point framework map including PRKAR2B. The analysis placed PRKAR1B as the most distal of the hitherto mapped 7p marker loci and resulted in an unequivocal order of pter-PRKAR1B-D7S21-D7S108-D7S17-D7S149- D7S62-cen, with a significantly higher rate of male than female recombination between PRKAR1B and D7S21. The 7q regulatory gene locus, PRKAR2B, could also be placed in an unambigous order with regard to the existing CEPH database 7q marker loci, the resulting order being cen-D7S371-(COL1A2,D7S79)-PRKAR2B-MET-D7S87++ +-TCRB-qter. Furthermore, in situ hybridization to metaphase chromosomes physically mapped PRKAR2B to band q22 on chromosome 7.

Chromosome 12 in human testicular cancer: dosage changes and their parental origin

Cytogenetically, a marker chromosome interpreted as i(12p) is present in most testicular tumors of germ cell origin. In this study, 22 patients with testicular germ-cell tumors were investigated by Southern blot hybridization to characterize changes in chromosome 12. In comparison with normal DNA, tumor DNA of 18 patients showed increased dosages of 12p accompanied by a comparable or smaller increase or no change in the dosage of centromeric sequences of chromosome 12. A likely interpretation was that most testicular tumors had one or several isochromosomes for 12p that were formed by somatic division of the centromere and that the points of breakage and reunion in the centromeric region were different in different tumors. Allelic 12p fragments showing increased intensity were paternal in four and maternal in three of seven informative cases. Thus, there was no evidence of sex-limited parental imprinting. Furthermore, the observed patterns of allelic fragments suggested that the marker was an i(12p) formed by sister chromatids of one homolog number 12 rather than the result of interchange of genetic material between different homologues.

Linkage disequilibrium mapping in isolated founder populations: diastrophic dysplasia in Finland

Linkage disequilibrium mapping in isolated populations provides a powerful tool for fine structure localization of disease genes. Here, Luria and Delbrück's classical methods for analysing bacterial cultures are adapted to the study of human isolated founder populations in order to estimate (i) the recombination fraction between a disease locus and a marker; (ii) the expected degree of allelic homogeneity in a population; and (iii) the mutation rate of marker loci. Using these methods, we report striking linkage disequilibrium for diastrophic dysplasia (DTD) in Finland indicating that the DTD gene should lie within 0.06 centimorgans (or about 60 kilobases) of the CSF1R gene. Predictions about allelic homogeneity in Finland and mutation rates in simple sequence repeats are confirmed by independent observations.

Gelsolin-derived familial amyloidosis caused by asparagine or tyrosine substitution for aspartic acid at residue 187

Dominantly inherited familial amyloidosis, Finnish type (FAF) is caused by the accumulation of a 71-amino acid amyloidogenic fragment of mutant gelsolin (GSN). FAF is common in Finland but is very rare elsewhere. In Finland and in two American families, the mutation is a G654A transition leading to an Asp to Asn substitution at residue 187. We found the same mutation in a Dutch family but a Danish FAF family had a G654T mutation, predicting Asp to Tyr at residue 187. We also found the G654T transversion in a Czech family. Using GSN polymorphisms, different haplotypes were found in the Danish and Czech families. We conclude that substitution of the uncharged Asn or Tyr for the acidic Asp at residue 187 creates a conformation that may be preferentially amyloidogenic for GSN.

Familial amyloidosis, Finnish type: G654----a mutation of the gelsolin gene in Finnish families and an unrelated American family

The Finnish type of familial amyloid polyneuropathy (FAF) is an autosomal dominant form of systemic amyloidosis caused by a mutation in the gelsolin gene. The mutation leads to the expression of amyloidogenic mutant Asp187----Asn gelsolin, an actin-modulating protein. We previously developed a DNA test based on amplification by the polymerase chain reaction followed by allele-specific oligonucleotide hybridization that identifies the base substitution adenine for guanine at nucleotide 654 in the gelsolin gene causing the disease. We show here that the same mutation is present in members of six apparently unrelated Finnish families and in a member of an unrelated American family. These results, taken together with previously published findings in nine additional Finnish families and another unrelated American family, indicate that most, perhaps all, FAF patients in Finland and possibly worldwide carry the same mutation. We suggest two alternative explanations: (i) the mutation arose in a very early common ancestor or (ii) the Asn187 mutation is particularly, perhaps uniquely, amyloidogenic.

Identical genetic locus for Baltic and Mediterranean myoclonus

Genetic linkage analysis shows that Baltic and Mediterranean myoclonus, two forms of progressive myoclonus epilepsy, are closely linked to marker D21S113 on the long arm of chromosome 21. Baltic and Mediterranean myoclonus are most probably due to mutations of the same gene.

Aberrant splicing of the CHM gene is a significant cause of choroideremia

Choroideremia (CHM) is an X-linked progressive degeneration of the choroid and retina. 12% of unrelated male patients carry deletions of the partially cloned CHM gene. In Finland, there are more than 120 living CHM patients belonging to eight apparently unrelated pedigrees. Molecular deletions involving the CHM gene have been detected in three families. We have screened the remaining five families for point mutations. In one large family a single nucleotide (T) insertion into the donor splice site of exon C leads to two aberrantly spliced mRNAs both producing a premature stop codon. The mutation can be assayed easily by amplification and digestion with Msel. Our findings provide additional evidence for the pathogenetic role of CHM mutations and provide a diagnostic tool for one fifth of the world's known CHM patients.

Evolution of zinc finger-Y and zinc finger-X genes in oryzomyne-akodontine rodents (Cricetidae)

Zinc finger-Y (Zfy) and zinc finger-X (Zfx) genes were analyzed by Southern blotting in male and female specimens of 10 species belonging to the oryzomyne-akodontine stock of Cricetidae rodents. DNA fragments were used as characters to construct a parsimony tree of the genes. Zfx and Zfy trees in general coincide with the evolutionary history of the taxa. Both trees show Oryzomys longicaudatus genes as the outgroup whereas Akodon xanthorrhinus genes are also distant from those of the other species. Oxymycterus rufus and Bolomys obscurus share related sequences, while genes from the other six Akodon species form a group of their own. It was found that 9 out of the 10 species analyzed show Zfy amplification in a range varying from 2 to 24 copies and with a pattern that is clade specific. The estimation of the average changes per character strongly suggests that Zfy has evolved more rapidly than Zfx; our estimates of the rate of nucleotide substitution are 4.6 times higher for Zfy than for Zfx.

A linkage map spanning the locus for diastrophic dysplasia (DTD)

Diastrophic dysplasia (DTD) is an autosomal recessive osteochondrodysplasia. Patients have short-limbed short stature and suffer from generalized joint dysplasia. We have recently mapped DTD to the distal long arm of chromosome 5. Here we report the localization of DTD in relation to 16 polymorphic markers on distal 5q. No recombinations occurred with two loci, D5S72 and D5S66. One presumptive candidate gene, osteonectin (SPARC), could be excluded on the basis of three recombinations with the DTD locus. Multipoint linkage analysis performed against a fixed order of markers placed DTD between glucocorticoid receptor (GRL) and SPARC favored by the odds of 33:1 over the next best location of DTD between D5S72 and D5S55. The sex-averaged distance between the definite flanking markers, GRL and D5S55, is 17.5 cM. From previously reported data on the physical localization of markers, we conclude that the DTD locus is in 5q31-q34.

Evidence supporting exclusion of the DCC gene and a portion of chromosome 18q as the locus for susceptibility to hereditary nonpolyposis colorectal carcinoma in five kindreds

Hereditary non-polyposis colorectal carcinoma (HNPCC) syndrome is characterized by early onset and multiple cancers of predominantly the proximal colon and occasionally other organs. The mode of transmission is compatible with autosomal dominant inheritance but the location and characteristics of the putative susceptibility gene are unknown. We performed linkage analyses with the aim of proving or excluding the existence of a susceptibility locus on 18q. This hypothesis was based on the frequent involvement of the DCC gene in colorectal carcinoma and on the previously reported linkage between HNPCC and the Kidd blood group locus (JK) also on 18q. Seven HNPCC families were tested with eight polymorphisms, including three from within DCC. The DCC locus could be excluded as the HNPCC susceptibility locus in five families in which the two point logarithm-of-odds scores were -3.66, -3.63, -4.12, -7.90, and -3.74 at the recombination fraction of 0.00. In the remaining two families linkage could be neither excluded nor confirmed. The added pairwise logarithm-of-odds score for all seven families was -22.65 at the recombination fraction of 0.00. Multipoint analyses of linkage in the seven families suggested exclusion of some 60 cM in the region DCC-D18S18-D18S22-D18S7 as the site for HNPCC susceptibility locus. In addition to DCC, the excluded portion comprises JK.

Choroideremia: linkage analysis with physically mapped close DNA-markers

We report linkage studies in 18 choroideremia (TCD) families using four closely linked polymorphic markers. Probe pZ11, which is known to be deleted in several unrelated patients with TCD, showed no recombinations (zeta max 15.63 at theta = 0.00). In contrast, one recombination was observed with DXS367, which is also physically very close to TCD. Loci DXS95 and DXYS69 each showed more than one recombination with TCD. Moreover, these analyses revealed a double crossover between TCD and DXYS1, changing the previously reported very close linkage to a recombination fraction of 0.04 with a lod score of 9.93. Multipoint linkage analysis placed TCD proximal to DXS95-DXYS69 and very close to DXS367-pZ11 with almost identical multipoint lod score maxima either proximal to DXS367 (zeta max = 23.43) or proximal to pZ11 (zeta max = 23.36). These results provide a refined linkage map around TCD and will also be useful in DNA diagnostics of the disease.

Oncogenes in human testicular cancer: DNA and RNA studies

Oncogene dosage and expression were studied in 16 testicular neoplasms, 14 of germ cell and two of non-germ cell origin. In comparison with normal DNA, tumour DNA of a total of eight patients (seven with germ cell neoplasm and one with testicular lymphoma) showed increased dosages of KRAS2, PDGFA, EGFR, MET and PDGFB. The most frequent (occurring in six tumours) and prominent (up to 3-4-fold) increases were detected in the dosages of KRAS2 (on chromosome 12p) and PDGFA (chromosome 7p), relative to a reference locus from chromosome 2. Importantly, there was a similar increase in 12p dosage in general in these tumours, suggesting the presence of the characteristic isochromosome 12p marker. On the contrary, possible 7p polysomy (assessed by molecular methods) did not explain the PDGFA (or EGFR) changes in all cases. NRAS, MYCN, CSFIR, MYB, MYC, ABL, HRASI, TP53, and ERBB2 did not reveal any consistent alterations in tumour DNA. In RNA dot blot assays the expression of KRAS2, PDGFA, EGFR, or MYC was generally not increased in the tumour samples when compared to that in normal testicular tissue of the same patients although there was interindividual variation in mRNA levels. It thus appears that while oncogene dosage changes occur in a proportion of testis cancers, they are often part of changes in large chromosomal regions or whole arms and are seldom accompanied by altered expression.