A comprehensive genetic map of the human genome based on 5,264 microsatellites

The great increase in successful linkage studies in a number of higher eukaryotes during recent years has essentially resulted from major improvements in reference genetic linkage maps, which at present consist of short tandem repeat polymorphisms of simple sequences or microsatellites. We report here the last version of the Généthon human linkage map. This map consists of 5,264 short tandem (AC/TG)n repeat polymorphisms with a mean heterozygosity of 70%. The map spans a sex-averaged genetic distance of 3,699 cM and comprises 2,335 positions, of which 2,032 could be ordered with an odds ratio of at least 1,000:1 against alternative orders. The average interval size is 1.6 cM; 59% of the map is covered by intervals of 2 cM at most and 1% remains in intervals above 10 cM.

A radiation hybrid map of the human genome

We have developed a panel of whole-genome radiation hybrids by fusing irradiated diploid human fibroblasts with recipient hamster cells. This panel of 168 cell lines has been typed with microsatellite markers of known genetic location. Of 711 AFM genetic markers 404 were selected to construct a robust framework map that spans all the autosomes and the X chromosome. To demonstrate the utility of the panel, 374 expressed sequence tags (ESTs) previously assigned to chromosomes 1, 2, 14 and 16 were localized on this map. All of these ESTs could be positioned by pairwise linkage to one of the framework markers with a LOD score of greater than 8. The whole genome radiation hybrid panel described here has been used as the starting material for the Genebridge4 panel that is being made widely available for genome mapping projects.

Genetic linkage mapping of the human steroid 5 alpha-reductase type 2 gene (SRD5A2) close to D2S352 on chromosome region 2p23-->p22

Two steroid 5 alpha-reductase isoenzymes catalyze the conversion of testosterone into dihydrotestosterone, the more bioactive androgen, which is essential for male phenotypic sexual differentiation and for androgen-mediated growth of such tissues and organs as the prostate. Inherited mutations in SRD5A2 cause male pseudohermaphroditism. The SRD5A1 and SRD5A2 genes encoding the steroid 5 alpha-reductase type 1 and type 2 isoenzymes have been previously assigned by in situ hybridization to 5p15 and 2p23, respectively. To map the SRD5A2 gene by linkage analysis, a novel RsaI RFLP detected in exon I and a TA repeat polymorphism found in exon V were genotyped in eight CEPH reference families. A two-point linkage analysis was performed between these polymorphisms and the chromosome 2 microsatellite markers of Généthon and NIH/CEPH. The closest linkage was observed with D2S352 (Zmax = 24.06; thetamax = 0.001) in the region 2p23-->p22. To further define the localization of SRD5A2, a framework map, including nine Généthon markers flanking the polymorphic SRD5A2 locus, was built by multipoint linkage analysis. This led to a high-resolution genetic map of the region flanking the polymorphic SRD5A2 gene, including the nine Généthon markers and three NIH/CEPH markers, yielded the following order: tel-D2S48-D2S149-D2S320-D2S171-D2S165- [D2S352/SRD5A2]-D2S367-[D2S19/D2S177]-[ D2S391/CALM]-D2S378-cen.

A 10-cM YAC contig spanning GLC1A, the primary open-angle glaucoma locus at 1q23-q25

Primary open-angle glaucoma is a complex of ocular disorders characterized by irreversible lesions of the optic nerve, open angle of the anterior chamber of the eye and elevated intraocular pressures. GLC1A, a locus involved in one form of this disease, has been mapped to an approximately 9-cM interval within 1q23-q25, between markers D1S445 and D1S416/D1S480. A 10-cM yeast artificial chromosome (YAC) contig spanning the whole region is described. This contig is based on 67 YACs, and 41 sequence tagged sites comprising 23 genetic markers, 16 YAC ends and 2 expressed sequence tags. The reagents reported in this study should be useful tools for the identification of the GLC1A gene by positional cloning.

An STS-based map of the human genome

A physical map has been constructed of the human genome containing 15,086 sequence-tagged sites (STSs), with an average spacing of 199 kilobases. The project involved assembly of a radiation hybrid map of the human genome containing 6193 loci and incorporated a genetic linkage map of the human genome containing 5264 loci. This information was combined with the results of STS-content screening of 10,850 loci against a yeast artificial chromosome library to produce an integrated map, anchored by the radiation hybrid and genetic maps. The map provides radiation hybrid coverage of 99 percent and physical coverage of 94 percent of the human genome. The map also represents an early step in an international project to generate a transcript map of the human genome, with more than 3235 expressed sequences localized. The STSs in the map provide a scaffold for initiating large-scale sequencing of the human genome.

Genetic linkage mapping of the dehydroepiandrosterone sulfotransferase (STD) gene on the chromosome 19q13.3 region

In the human liver and adrenal, there is a single hydroxysteroid sulfotransferase, which catalyzes the transformation of dehydroepiandrosterone to dehydroepiandrosterone sulfate, the most abundantly circulating steroid in humans, and also catalyzes the sulfation of a series of other 3 beta-hydroxysteroids as well as cholesterol. Dehydroepiandrosterone sulfate serves as precursor for the formation of active androgens and estrogens in several peripheral tissues, indicating that hydroxysteroid sulfotransferase plays a pivotal role in controlling the hormonal action of sex steroids by regulating their bioavailability. We recently elucidated the structure of the gene encoding hydroxysteroid sulfotransferase (STD), also designated dehydroepiandrosterone sulfotransferase, which spans 17 kb and contains six exons. The STD gene was preliminarily assigned to chromosome 19 by polymerase chain reaction (PCR) amplification of DNA from a panel of human/rodent somatic cell hybrids. To locate the STD gene, the novel biallelic polymorphism found in intron 2 was genotyped in eight CEPH reference families by direct sequencing of PCR products. Two-point linkage analysis was first performed between the latter polymorphism and chromosome 19 markers from Généthon and NIH/CEPH. The closest linkage was observed with D19S412 (Zmax = 9.23; theta max 0.038) and HRC (Zmax = 5.95; theta max 0.036), located on the 19q13.3 region. A framework map including six Généthon markers flanking the polymorphic STD gene was created by multipoint linkage analysis. Thereafter, a high-resolution genetic map of the region was constructed, yielding to the following order: qter-D19S414-D19S224-D19S420-D19S217-(APOC2++ +-D19S412)- (STD-HRC)-KLK-D19S22-D19S180-PRKCG-D19S418 -tel.

A common gene for juvenile and adult-onset primary open-angle glaucomas confined on chromosome 1q

Primary open-angle glaucoma (POAG), which causes progressive loss of the visual fields, was subdivided into two groups according to age at onset: (1) chronic open-angle glaucoma (COAG) diagnosed after age 40 years and (2) juvenile open-angle glaucoma (JOAG) diagnosed between 3 years of age and early adulthood. A JOAG gene (GLC1A) was recently mapped to chromosome 1q. We studied 142 members of a huge multigenerational French Canadian family affected with autosomal dominant POAG. Either JOAG or COAG was diagnosed in 40 patients. Six subjects were also diagnosed with ocular hypertension (OHT), which may lead to POAG. To localize a common disease gene that might be responsible for both glaucoma subsets, we performed linkage analysis considering JOAG and COAG under the same phenotypic category. JOAG/COAG was tightly linked to seven microsatellite markers on chromosome 1q23-q25; a maximum lod score of 6.62 was obtained with AF-M278ye5. To refine the disease locus, we exploited a recombination mapping strategy based on a unique founder effect. The same characteristic haplotype, composed of 14 markers spanning 12 cM between loci D1S196 and D1S212, was recognized in all persons affected by JOAG, COAG, or OHT, but it did not occur in unaffected spouses and in normal family members > 35 years of age, except for three obligatory carriers. Key recombination events confined the disease region within a 9-cM interval between loci D1S445 and D1S416/D1S480. These observations demonstrate that the GLC1A gene is responsible for both adult-onset and juvenile glaucomas and suggest that the JOAG and COAG categories within this family may be part of a clinical continuum artificially divided at age 40 years.

Mapping of the HSD17B2 gene encoding type II 17 beta-hydroxysteroid dehydrogenase close to D16S422 on chromosome 16q24.1-q24.2

The enzymes of the 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) gene family are responsible for a key step in the formation and degradation of androgens and estrogens: catalyzing the interconversion of 17-ketosteroids and their active 17 beta-hydroxysteroid counterparts. The structure of human type II 17 beta-HSD cDNA was recently reported. This enzyme catalyzes the interconversion of delta 4-androstenedione and testosterone, androstanedione and dihydrotestosterone, and estrone and 17 beta-estradiol, whereas type I 17 beta-HSD catalyzes exclusively the interconversion of estrogens. To locate the HSD17B2 gene, the novel dinucleotide CA repeat sequence found 571 bp downstream from the end of exon 1 was genotyped into eight CEPH reference families by PCR. Two-point linkage analysis was performed between the latter polymorphism and the 2066 microsatellite markers of Généthon. The maximal pairwise lod score (Zmax = 33.3) with a maximal recombination fraction (theta max) of 0.008 was obtained with the marker D16S422 located on 16q24.1-q24.2. To define further the localization of the HSD17B2 gene, we constructed a high-resolution genetic map of the region flanking the polymorphic HSD17B2 gene including eight Généthon markers. The order of the HSD17B2 gene and markers is qter-D16S516-D16S504-D16S507-D16S505-D16S511+ ++-[HSD17B2-D16S422]-D16S520- D16S413-tel.

Genetic linkage mapping of HSD3B1 and HSD3B2 encoding human types I and II 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4-isomerase close to D1S514 and the centromeric D1Z5 locus

The enzyme 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4-isomerase (3 beta-HSD) catalyses an essential step in the biosynthesis of all steroid hormones. Consequently, classical 3 beta-HSD deficiency is responsible for a severe form of congenital adrenal hyperplasia. The HSD3B1 and HSD3B2 genes encoding the types I and II 3 beta-HSD isoenzymes, respectively, have been previously assigned by in situ hybridization to the chromosome 1p13.1 region. To determine the physical distance between these two genes, NotI and SacII digests of genomic DNA were resolved by pulse-field gel electrophoresis and hybridized with type I and type II 3 beta-HSD cDNAs used as probes. The detection of a single band under low stringency conditions indicates that HSD3B1 and HSD3B2 are located within an approximately 0.29 megabase SacII DNA fragment. We constructed a high resolution genetic map of the region flanking the polymorphic HSD3B1 and HSD3B2 genes including ten Généthon markers and the two NIH/CEPH markers AMY2B and D1Z5. The HSD3B1A and HSD3B2A markers were mapped relative to other reference markers through eight CEPH reference families. The order of polymorphic genes and markers is: pter-[AMY2B-D1S239]-D1S457-D1S502-D1S250-+ ++D1S252-[HSD3B1A -HSD3B2A-D1S514]-[D1Z5-D1S442]-D1S305-D 1S303-D1S484-qter. The D1S514 marker was thus closely linked to HSD3B1A (theta < 0.001; lod = 14.13) and HSD3B2 (theta = 0.008; lod = 35.36). The HSD3B loci are located 1-2 cM of the centromeric marker D1Z5.

The 1993-94 Généthon human genetic linkage map

In 1992, we described a second-generation genetic linkage map of the human genome. Using 1,267 new microsatellite markers, we now present a new genetic linkage map containing a total of 2,066 (AC)n short tandem repeats, 60% of which show a heterozygosity of over 0.7. Statistical linkage analysis based on the genotyping of eight large CEPH families placed these markers in the 23 linkage groups. The map includes 1,266 intervals and spans a total distance of 3690 centiMorgans (cM). A total of 1,041 markers could be ordered with odds ratios greater than 1000:1. About 56% of this map is at a distance of 1 cM or less from one of its markers.

Developmental plasticity in cerebellar tactile maps: fractured maps retain a fractured organization

Plasticity following deafferentation has been repeatedly demonstrated in topographic sensory maps in the mammalian brain. In this paper we investigated the developmental plasticity of the fractured somatotopic map found in the tactile regions of the rat cerebellum. At various stages of postnatal development between postnatal days 1 and 30, we cauterized the infraorbital branch of the trigeminal nerve, which innervates the upper lip, furry buccal pad, and vibrissae that are represented within cerebellar folium crus IIa. The organization of the crus IIa map was then examined 2 to 3 months after denervation. We found that tactile receptive fields had reorganized throughout the denervated area but maintained a fractured somatotopy. Comparison of the reorganization in different animals showed that the denervated upper lip region was consistently and predominantly replaced by representation of the upper incisors. Analysis of evoked field potentials revealed an alteration, in denervated animals, of the response of the granule cell layer to brief tactile stimulation. This response in normal animals consists of two components at different latencies. Animals lesioned later in development were less likely to have the short latency component. This result suggests a difference in the developmental sensitivity of different cerebellum-related pathways to nerve lesions.

A second-generation linkage map of the human genome

A linkage map of the human genome has been constructed based on the segregation analysis of 814 newly characterized polymorphic loci containing short tracts of (C-A)n repeats in a panel of DNAs from eight large families. Statistical linkage analysis placed 813 of the markers into 23 linkage groups corresponding to the 22 autosomes and the X chromosome; 605 show a heterozygosity above 0.7 and 553 could be ordered with odds ratios above 1,000:1. The distance spanned corresponds to approximately 90% of the estimated length of the human genome.

A craniometric study of bicoronal craniosynostosis (BCC)

We compared 20 cases of bicoronal craniosyntosis (BCC) using the linear and angular values of the normal statistical material for the same age and sex. The skull in BCC is significantly shortened and flattened but with normal width. The height of the frontal arch (FNBR) is significantly decreased. The base of the skull is depressed with angle AB2 significantly increased, and angle NTNO significantly decreased and, even in some cases, with negative angular values. This is inducing a sinking of LEA (length from N to T), and in some cases LEA is lower than the line LNO (distance from N to O). The cephalic index (CI) was significantly increased, and the calculated cranial capacity (CC) was significantly decreased. Bregma (BR) is moving anteriorly in BCC, inducing an anterior movement of the calvaria with a bulge around BR. In this anterior movement we designate lack of positive occipital rotation. In BCC there is an evident lack of positive occipital rotation. Superimposing our drawings on the reference line NBA, we found for the first time a movement of anatomical landmarks similar to that observed in the negative occipital rotation in vestibular orientation.

A craniometric study of sagittal craniosynostosis (SC)

Twenty cases of sagittal craniosynostosis (SC) were compared with the linear and angular values of the normal statistical material for the same age and sex. There were significantly increased values of the length of the skull (LI) and the height of the frontal arch (FNBR) and significantly decreased width (WI) and height of the skull (HI) as well as the depth of the cerebellar fossa (PEP). The length of the anterior cerebral fossa (LEA) remained within normal limits and the distance BRPI between bregma (BR) and the internal protuberance (PI) was within normal limits or increased. The angular value of the basal angle (angle NT-BA, AB2) decreased significantly and the angle NTNO (angle between the lines NT and NO) and the angle BRTPI (the angle between the lines TBR and TPI) were significantly increased. The cephalic index (CI) was significantly decreased. The cranial capacity (CC) is normal or decreased. There is demonstrated an occipital over-rotation of the skull.

NASPE young investigator awardee-1990. Complex rhythms resulting from overdrive suppression in electrically stimulated heart cell aggregates

Spontaneously beating embryonic chick heart cell aggregates were stimulated with current pulses delivered either as periodic trains, or at a fixed delay after each action potential. Following stimulation at fixed rates faster than the intrinsic rate, there was a transient slowing of the spontaneous rhythm. This response, called overdrive suppression, can lead to a complex evolution of rhythms. During periodic stimulation there is a continuum of dropped beat patterns, and during fixed delay stimulation bursting activity appears. This study provides a conceptual basis for understanding analogous rhythms in the intact heart.

[Comparative study of psychometric results of 2 french speaking populations with hypothyroidism detected at birth]

The authors compare the data from the psychological assessment of a cohort of 191 French speaking hypothyroid children detected by neonatal screening: 99 were followed in Quebec and 92 in Lille, according to two independent programs. Three age levels were selected: 12-18 months, 5 and 7 years. Data were similar and, in both studies, results of the later ages were slightly lower than the norms of the tests or results obtained in control groups. In both populations correlations were found between some results and two factors related to hypothyroidism: delayed bone surface development and thyroxinemia at the time of diagnosis. On the other hand, etiology and time of treatment had no repercussions on any group results.

Fumarylacetoacetase measurement as a mass-screening procedure for hereditary tyrosinemia type I

Fluorometric quantitative tyrosine determination on dried-blood spots is the primary neonatal screening test used for tyrosinemia type I (HT) in the province of Quebec. Succinylacetone determination on these same spots is used as the complementary test when the tyrosine level is higher than a given threshold. This procedure has proved to be less discriminant over the past few years because of changes in newborn feeding and because of early discharge of newborns from the nursery. We have developed an enzyme-linked immunosorbent assay (ELISA) to measure the deficient enzyme in HT in dried-blood spots. Fumarylacetoacetase (FAH) (E.C.3.7.1.2) was measured retrospectively by an ELISA on 25 dried-blood samples from proven patients with HT and prospectively in 72,000 specimens received in the neonatal screening program. In this pilot project, FAH was measured first, and, if necessary, succinylacetone was determined as the complementary test. All 25 samples from proven patients and specimens from four other patients detected in the pilot study have shown almost complete absence of FAH in dried-blood samples. At a cutoff level of 12.5% of normal adult blood spotted on the same type of paper, only 30 other cases disclosed FAH levels low enough to warrant succinylacetone measurement but had no detectable succinylacetone. The false-positive rate is thus 1:2,400 with this primary ELISA. However, blood transfusion in newborns prior to blood collection on filter paper may yield false-negative tests, since FAH is present in erythrocytes of normal donors.(ABSTRACT TRUNCATED AT 250 WORDS)

Myotonic dystrophy: linkage with apolipoprotein E and estimation of the gene carrier status with genetic markers

The genes for myotonic dystrophy (MD) and for apolipoprotein E (ApoE) belong to a chromosome 19 synthenic group of markers. A familial linkage analysis between MD and ApoE was performed using the J Ott LIPED program (IBM PC/XT, April 1984) to estimate the genetic distance between these 2 genes. Of a total of 136 individuals in 11 MD families, 81 were confirmed to be affected by the disease and 41 were asymptomatic. ApoE phenotypes were determined in 115 of these 122 individuals. No recombinant was observed out of 74 meioses which were informatives for both MD and the ApoE isoproteins. A global maximal lod score Z of 19.00 was obtained at the recombination fraction theta = 0. The upper theta value at the confidence interval corresponding to the peak lod score (Z max) - 1 was 0.03. This suggests that the loci for MD and ApoE are at a distance of 0 to 0.03 Morgan. Since ApoE and apolipoprotein C2 (ApoC2) have been shown by others to be about 40 kb apart, our data are therefore consistent with the distance estimate of 0.02 Morgan reported between MD and ApoC2. The D19S19 (LDR152) polymorphic DNA sequence is also tightly linked to MD on chromosome 19. The segregation of ApoE isoproteins and of ApoC2 and D19S19 DNA polymorphism was utilized for evaluating the probability for individuals at risk of inheriting the disease gene in MD families. Data are presented on 3 families to emphasize the usefulness of genetic markers to estimate the MD gene carrier status of asymptomatic individuals and also for those presenting a partial syndrome. The limitations of such approach are also discussed.

Hypertriglyceridemia and lower LDL cholesterol concentration in relation to apolipoprotein E phenotypes in myotonic dystrophy

Plasma lipid, lipoprotein levels and apolipoprotein apo E phenotypes were determined in 70 patients with myotonic dystrophy (MyD) and 81 controls. Marked differences were noticed in the apo E phenotype frequencies between the two groups. Plasma triglycerides and VLDL cholesterol were higher in MyD than controls, but only the latter was related to differences in the apo E phenotypes between two groups. Accordingly, the ratio of VLDL cholesterol/plasma triglycerides was increased significantly in MyD, suggesting accumulation of intermediary density particles due to lower affinity of E2 containing lipoproteins for lipoprotein cell receptors. The LDL cholesterol concentration was lower in MyD than controls and was related to differences in the apo E phenotype frequencies between the two groups. These results indicate increased removal of LDL particles in the apo E2 phenotypes, perhaps due to upregulation of LDL (B, E) receptor activity. Plasma cholesterol and HDL cholesterol concentrations were similar in both groups. Another feature of the study was lower levels of plasma cholesterol, triglycerides, VLDL and LDL cholesterol in the homozygous E4:E4 phenotype. These results suggest increased clearance rate of both VLDL and LDL particles and support the concept that apo E4-containing lipoproteins have higher in vivo affinity for ape E and/or B, E receptors.

Useful parameters to predict the eventual mental outcome of hypothyroid children

The Quebec Network for Genetic Medicine has followed the development of some 100 hypothyroid children treated by 1 month of age and evaluated at 18 months, 3 and 5 yr and the Griffiths Mental Development Scales, then at 7 and 9 yr with the Wechsler Intelligence Scale for Children Revised. Results show that the children as a group reach scores within the normal range of the tests. However, a few patients have low scores at each evaluation. Previously, we showed a correlation between a low serum thyroxine concentration, or a relatively retarded bone maturation before treatment, and low mental scores. To better characterize the significance of this relationship we correlated these pretreatment factors and the Wechsler Intelligence Scale for Children Revised results of 43 subjects reaching the age of 7 yr. Again, the same correlation was observed. Calculating a predictive factor (low thyroxine, less than 2 micrograms/dl and retarded bone surface, less than 0.05 cm2) from data recorded before therapy initiation, 10 of 13 children were correctly predicted to have I.Q. values less than 90. The use of these parameters might permit early intervention, and allow specific guidance of the more affected subjects.

[The distribution of surnames in the Saguenay and Charlevoix regions as indicators of population structure in the nineteenth and twentieth centuries]

"This paper presents a statistical analysis of surnames, revealing a striking similarity between the Saguenay and Charlevoix regions in the province of Quebec, since the 19th century. Indeed, a migration study also shows that the former region was created in the 1840's by immigrants coming mostly from the latter. An analysis by decade also shows that the Saguenay population structure has remained relatively stable since the middle of the 19th century. It is suggested that this kind of surnames analysis may be a useful indicator not only of the dynamics of a population, but also of the evolution of the whole gene pool. It seems however to reflect very poorly the movement or diffusion of any deleterious gene in particular." (SUMMARY IN ENG AND SPA)

Auditory brainstem response audiometry in congenitally hypothyroid children under early replacement therapy

Using auditory brainstem response audiometry, we evaluated 34 congenital hypothyroidism children under thyroid hormone therapy and 24 age- and sex-matched controls between 5 and 12 yr of age. Two main auditory brainstem response abnormalities were encountered: first, prolonged wave I latencies, secondary to a peripheral impairment, were found in seven congenital hypothyroidism children (20%): three of these showed signs of serious otitis media, unilaterally in two and bilaterally in the other, at the time of the evaluation. Second, shortened I-V interpeak latencies were observed in 10 children (29%). No correlation was found between the interpeak latencies and the L-thyroxine serum values at the time of the test or just prior to treatment initiation. Also, there was no correlation with estimated bone age at treatment initiation or with the Griffiths global mental development quotients assessed at 5 yr of age. These preliminary results suggest a significant incidence of auditory brainstem response abnormalities in treated hypothyroid children.