Malformation syndromes: a review of mouse/human homology

Covariance in human limb joint articular morphology

OBJECTIVES

Limb synovial joints exhibit complex shapes that must accommodate often-antagonistic demands of function, mobility, and stability. These demands presumably dictate coordination among joint articular shapes, but the structure of morphological covariance within and among joints is unknown. This study analyzes the human shoulder, elbow, hip, and knee to determine how articular covariance is structured in relation to joint structure, accessory cartilage, and function.

MATERIALS AND METHODS

Surface models were created from the CT scans of 200 modern skeletons from the University of Tennessee Donated Skeletal Collection. Three-dimensional landmarks were collected on the shoulder, elbow, hip, and knee joints. Two-block partial least squares were conducted to determine associations between surfaces of conarticular shapes, functionally analogous articulations, and articulations belonging to the same bone.

RESULTS

Except for the components of the shoulder, all conarticular pairs exhibit covariance, though the strength of these relationships appears unrelated to the amount of accessory cartilage in the joint. Only the analogous articulations of the humerus and femur exhibit significant covariance, but it is unlikely that this pattern is due to function alone. Stronger covariance within the lower limb than the upper limb is consistent broader primate patterns of within-limb integration.

DISCUSSION

With the exception of the elbow, complementary joint function does not appear to promote strong covariance between articulations. Analogous humeral and femoral surfaces are also serially homologous, which may result in the articular associations observed between these bones. Broadly, these patterns highlight the indirect relationship between joint congruence and covariance.

Novel frem1-related mouse phenotypes and evidence of genetic interactions with gata4 and slit3

The FRAS1-related extracellular matrix 1 (FREM1) gene encodes an extracellular matrix protein that plays a critical role in the development of multiple organ systems. In humans, recessive mutations in FREM1 cause eye defects, congenital diaphragmatic hernia, renal anomalies and anorectal malformations including anteriorly placed anus. A similar constellation of findings-microphthalmia, cryptophthalmos, congenital diaphragmatic hernia, renal agenesis and rectal prolapse-have been described in FREM1-deficient mice. In this paper, we identify a homozygous Frem1 missense mutation (c.1687A>T, p.Ile563Phe) in an N-ethyl-N-nitrosourea (ENU)-derived mouse strain, crf11, with microphthalmia, cryptophthalmos, renal agenesis and rectal prolapse. This mutation affects a highly conserved residue in FREM1's third CSPG domain. The p.Ile563Phe change is predicted to be deleterious and to cause decreased FREM1 protein stability. The crf11 allele also fails to complement the previously described eyes2 allele of Frem1 (p.Lys826*) providing further evidence that the crf11 phenotype is due to changes affecting Frem1 function. We then use mice bearing the crf11 and eyes2 alleles to identify lung lobulation defects and decreased anogenital distance in males as novel phenotypes associated with FREM1 deficiency in mice. Due to phenotypic overlaps between FREM1-deficient mice and mice that are deficient for the retinoic acid-responsive transcription factor GATA4 and the extracellular matrix protein SLIT3, we also perform experiments to look for in vivo genetic interactions between the genes that encode these proteins. These experiments reveal that Frem1 interacts genetically with Gata4 in the development of lung lobulation defects and with Slit3 in the development of renal agenesis. These results demonstrate that FREM1-deficient mice faithfully recapitulate many of the phenotypes seen in individuals with FREM1 deficiency and that variations in GATA4 and SLIT3 expression modulate some FREM1-related phenotypes in mice.

Deficiency of FRAS1-related extracellular matrix 1 (FREM1) causes congenital diaphragmatic hernia in humans and mice

Congenital diaphragmatic hernia (CDH) is a common life-threatening birth defect. Recessive mutations in the FRAS1-related extracellular matrix 1 (FREM1) gene have been shown to cause bifid nose with or without anorectal and renal anomalies (BNAR) syndrome and Manitoba oculotrichoanal (MOTA) syndrome, but have not been previously implicated in the development of CDH. We have identified a female child with an isolated left-sided posterolateral CDH covered by a membranous sac who had no features suggestive of BNAR or MOTA syndromes. This child carries a maternally-inherited ~86 kb FREM1 deletion that affects the expression of FREM1's full-length transcripts and a paternally-inherited splice site mutation that causes activation of a cryptic splice site, leading to a shift in the reading frame and premature termination of all forms of the FREM1 protein. This suggests that recessive FREM1 mutations can cause isolated CDH in humans. Further evidence for the role of FREM1 in the development of CDH comes from an N-ethyl-N-nitrosourea -derived mouse strain, eyes2, which has a homozygous truncating mutation in Frem1. Frem1(eyes2) mice have eye defects, renal agenesis and develop retrosternal diaphragmatic hernias which are covered by a membranous sac. We confirmed that Frem1 is expressed in the anterior portion of the developing diaphragm and found that Frem1(eyes2) embryos had decreased levels of cell proliferation in their developing diaphragms when compared to wild-type embryos. We conclude that FREM1 plays a critical role in the development of the diaphragm and that FREM1 deficiency can cause CDH in both humans and mice.

Genetic analysis of fin development in zebrafish identifies furin and hemicentin1 as potential novel fraser syndrome disease genes

Using forward genetics, we have identified the genes mutated in two classes of zebrafish fin mutants. The mutants of the first class are characterized by defects in embryonic fin morphogenesis, which are due to mutations in a Laminin subunit or an Integrin alpha receptor, respectively. The mutants of the second class display characteristic blistering underneath the basement membrane of the fin epidermis. Three of them are due to mutations in zebrafish orthologues of FRAS1, FREM1, or FREM2, large basement membrane protein encoding genes that are mutated in mouse bleb mutants and in human patients suffering from Fraser Syndrome, a rare congenital condition characterized by syndactyly and cryptophthalmos. Fin blistering in a fourth group of zebrafish mutants is caused by mutations in Hemicentin1 (Hmcn1), another large extracellular matrix protein the function of which in vertebrates was hitherto unknown. Our mutant and dose-dependent interaction data suggest a potential involvement of Hmcn1 in Fraser complex-dependent basement membrane anchorage. Furthermore, we present biochemical and genetic data suggesting a role for the proprotein convertase FurinA in zebrafish fin development and cell surface shedding of Fras1 and Frem2, thereby allowing proper localization of the proteins within the basement membrane of forming fins. Finally, we identify the extracellular matrix protein Fibrillin2 as an indispensable interaction partner of Hmcn1. Thus we have defined a series of zebrafish mutants modelling Fraser Syndrome and have identified several implicated novel genes that might help to further elucidate the mechanisms of basement membrane anchorage and of the disease's aetiology. In addition, the novel genes might prove helpful to unravel the molecular nature of thus far unresolved cases of the human disease.

There are a large number of human genetic syndromes with limb and digit deformities. It has been shown that the genes underlying these syndromes are well conserved in evolution, and most perform the same role even in the fins of fish. One such human syndrome is Fraser Syndrome, characterized by a number of defects including fusion of the fingers (syndactyly). Data obtained with corresponding mouse mutants suggest that all of these defects are due to transient basement membrane disruptions and epithelial blistering during development. Whilst some of the Fraser Syndrome genes have been identified, others are unknown. We show that mutation of the known Fraser Syndrome genes in zebrafish generate comparable blistering defects in the fins. Importantly, we have also identified additional genes and mechanisms required for the same processes. Included in this are hemicentin1, a gene whose function had thus far only been studied in nematodes, and furinA, encoding a proprotein convertase, for which we reveal a novel role in ectodomain shedding of Fras/Frem proteins. This work thus expands our understanding, not only of Fraser Syndrome, but also of the common processes of basement membrane formation and function during fin and limb development.

The genetics of Fraser syndrome and the blebs mouse mutants

Fraser syndrome is a recessive multisystem disorder characterized by embryonic epidermal blistering, cryptophthalmos, syndactyly, renal defects and a range of other developmental abnormalities. More than 17 years ago, the family of four mapped mouse blebs mutants was proposed as models of this disorder, given their striking phenotypic overlaps. In the last few years, these loci have been cloned, uncovering a family of three large extracellular matrix proteins and an intracellular adapter protein which are required for normal epidermal adhesion early in development. The proteins have also been shown to play a crucial role in the development and homeostasis of the kidney. We review the cloning and characterization of these genes and explore the consequences of their loss.

A genetic study of the human T gene and its exclusion as a major candidate gene for sacral agenesis with anorectal atresia

Sacral agenesis is a heterogeneous group of congenital anomalies in which most cases are sporadic but rare familial forms also occur. Although one gene has been mapped to chromosome 7q36 in families with hemisacrum, associated with anorectal atresia and presacral mass, it is clear that the genetic aetiology of these disorders is complex and other genes remain to be discovered. Some years ago, the idea of T (Brachyury) as a candidate gene for sacral agenesis was raised, because tail abnormalities associated with T and the t complex, on mouse chromosome 17, resemble spinal defects seen in man. The recent cloning and mapping of the human T gene prompted us to re-evaluate this idea. T is a transcription factor essential for the normal development of posterior mesodermal structures. Although the sequence and function of T are highly conserved in evolution, our genetic study shows that the coding region of the human gene is highly polymorphic. Three common variable amino acid sites in known functional domains have been identified: Gly356Ser, Asn369Ser, and Gly177Asp. For the latter variant, functional studies have shown that the presence of Asp at residue 177 reduces the stability of T dimer formation. A search for rare mutation of T in 28 selected patients with sacral agenesis/anorectal atresia identified a novel, rare variant in one patient and her mother. This mutation leads to an amino acid change within a conserved activation domain. While the functional significance of this single mutation requires further investigation, we can conclude from our studies that if T has a role in the aetiology of sacral agenesis, its contribution is small in this particular set of patients. However, we cannot exclude a more major role in other forms of sacral defect.

Lack of evidence of a major gene acting on postaxial polydactyly in South America

Data on polydactyly were obtained from two large samples: the Latin American Collaborative Study of Congenital Malformations (ECLAMC), and from a migrant Northeastern Brazilian population of rural origin (Hospedaria). ECLAMC is a case-control clinical epidemiological program comprising 10,035 individuals distributed among 2,030 segregating nuclear families. Hospedaria data consisted of 6,586 examined individuals belonging to 1,040 nuclear families. Using complex segregation analysis methodology we found no evidence of two loci (a major gene and a modifier locus) acting on postaxial polydactyly in the present study. Very high heritability values (in a classical multifactorial model) of postaxial polydactyly were detected, for several sets of analyses in ECLAMC and in Hospedaria. For the whole ECLAMC sample there is a peculiar suggestion of a major recessive gene effect responsible for the trait; however, no comparison with a model involving transmission probabilities (tau) was possible in this highly heterogeneous sample. If the whole ECLAMC sample is divided in subsamples, according to Black admixture proportions, the same multifactorial picture emerges. Two different inheritance patterns were verified for hand (HP) and foot (FP) postaxial polydactyly: For HP there is evidence of a non-Mendelian transmission mechanism, while for FP the parental/sib transmission appears to be due only to multifactorial causes.

Hand and foot postaxial polydactyly: two different traits

The aim of this work was to test whether postaxial hexadactyly had different clinical and epidemiological characteristics depending on hand or foot involvement. In the period 1967-1993, the Latin-American Collaborative Study of Congenital Malformations (ECLAMC) enrolled 1,582,289 births, and 2,271 cases with isolated (nonsyndromal) postaxial polydactyly (5th-digit hexadactyly). The prevalence was 14.3/10,000 births. Postaxial polydactyly (PP) of the hand (HPP) was the most frequent type (N:1,733; 76.3%; prevalence: 11.0/10,000), followed by foot PP (FPP=N:351; 15.5%; prevalence: 2.2), and hand and foot PP (BPP=N:187; 8.2%; prevalence: 1.2). Unlike HPP (55.0% bilateral; 77.2% left), FPP was less frequently bilateral (19.4%), with lower preference for the left side (55.5%). As expected, HPP was associated with African Black ethnicity, male sex, twinning, low maternal education, parental consanguinity, and there was frequent recurrence in 1st-degree relatives. Conversely, FPP was associated with Amerindian racial background, parental subfertility, and bleeding in the 1st trimester of pregnancy. BPP displayed the highest frequency of associated congenital defects (23.4%, vs HPP:6.6%, FPP: 15.4%). In its isolated form, BPP resembled HPP more than FPP with respect to left preference (90.9%), familial recurrence (11.0% of 1st degree relatives), and low maternal education. Although male sex preference and high frequency of twinning was observed in the 3 PP subtypes, statistical significance was present only in HPP. None of the 3 PP subtypes showed abnormal values for perinatal mortality, birth weight, length of gestation, parental ages, or parity. A logistic regression analysis showed Black race only to be associated with HPP, parental subfertility with FPP, parental consanguinity with BPP, and non-Black race with both FPP and BPP. The data presented here are the first indication that HPP and FPP are 2 different entities, with a larger genetic component in HPP than in FPP.

Epidemiological analysis of rare polydactylies

This work includes all cases with extra digits (polydactyly) registered from a birth sample of over four million births aggregated from two comparable birth series: the Latin-American Collaborative Study of Congenital Malformations: ECLAMC (3,128,957 live and still births from the 1967 to 1993 period), and the Spanish Collaborative Study of Congenital Malformations: ECEMC (1,093,865 livebirths from April 1976 to September 1993, and 7,271 stillbirths from January 1980 to September 1993). All but 2 of 6,912 registered polydactyly cases fit well into one of the following 11 preestablished polydactyly types (observed number of cases in parentheses): Postaxial hexadactyly (5,345), Preaxial-I hexadactyly (1,018), Seven or more digits (57), synpolydactyly (15), crossed polydactyly (45), 1st digit triphalangism (33), 2nd digit duplication (39), 3rd digit duplication (18), 4th digit duplication (22), Haas polysyndactyly (3), and high degree of duplication (4). The birth prevalence rates observed in both series were similar except for postaxial polydactyly, which was more frequent in the ECLAMC (150.2/100,000) than in the ECEMC (67.4/100,000), as expected due to the higher African Black ethnic extraction of the South-American than of the Spanish populations. This similar frequency for the rare polydactylies (5.4 per 100,000 in South America and 5.7 in Spain), and for each one of the 9 categories, suggests that the values reported here are valid for most populations. The rare polydactylies are frequently syndromal: one third of them (77/236) were found in association with other congenital anomalies, 11.0% (26/236) in MCA cases and 21.6% (51/236) in recognized syndromes.

The dysmorphic human-mouse homology database (DHMHD): an interactive World-Wide Web resource for gene mapping

Genetic mapping and the examination of "candidate genes" for isolating loci associated with clinical syndromes can be greatly accelerated if there is information about where in the genome a particular locus might be situated. Such clues can come from homology to mouse mutants that have been mapped and knowledge of homology between mouse and human chromosomal segments. Further clues can come from chromosome aberrations giving a similar phenotype. However, these clues are often scattered widely in published reports, and even if they are collected together in catalogues or databases there is no rapid way of moving from one data type to another. The Dysmorphic Human and Mouse Homology Database (DHMHD) is designed to ease this data transition. DHMHD comprises detailed information from four separate sources and enables cross referencing through phenotypic and chromosome homology. The DHMHD system is a prototype which is now available online through the World-Wide Web.

Inherited disorders: the comparative picture

When confronted with a novel familial disorder, veterinarians should consult McKusick's catalogue of inherited disorders in humans, called Mendelian Inheritance in Man (MIM), or its online version (OMIM), to see whether a similar disorder has been reported in humans. They should also consult the other readily available sources of comparative information on mice and domesticated species. Increasingly, such consultations can be conducted on the Internet via the World Wide Web. If it is thought that an animal disorder is homologous with a human disorder, publications describing the animal disorder should include the MIM number(s) for that disorder. Future research can then test the hypothesis of homology, until a consensus is reached.

The locus for Meckel syndrome with multiple congenital anomalies maps to chromosome 17q21-q24

Autosomal recessive Meckel syndrome (OMIM 249000) (MES), first described in 1822 by Johann F. Meckel, is a major monogenic malformation syndrome with a neural tube defect leading to death of the fetus in utero or shortly after birth. The hallmarks of the syndrome are occipital meningoencephalocele, very large kidneys with multicystic dysplasia, cystic and fibrotic changes of the liver and polydactyly (Fig. 1). Other typical malformations for MES are cleft lip and palate, urinary tract anomalies, ambiguous genitals in the males and club feet. Although MES has been reported worldwide, reports on the true birth prevalence of MES in different populations are scarce. In Finland MES is effectively screened and relatively frequent with a birth prevalence of 1:9,000 and a disease gene frequency of 0.01 (ref.4) which is of the same order of magnitude as that of the most common recessive diseases belonging to the 'Finnish disease heritage', that is genetic disorders enriched or only encountered in Finland. However, in MES, comparable or even higher incidences are also reported from other populations. Here, we report the assignment of the MES locus to chromosome 17q21-q24 in the 13 cM region, and exclude some of the potential candidate genes located in this critical chromosomal region.

A large Turkish kindred with syndactyly type II (synpolydactyly). 2. Homozygous phenotype?

Syndactyly type II (synpolydactyly (SPD)) is an autosomal dominant condition with typical abnormalities of the distal parts of both upper and lower limbs. We report here a previously undescribed phenotypic feature of people with severe hand and foot deformities who were born to two affected parents. This is the first example of SPD subjects manifesting a very distinctive phenotype, suggesting that they must be homozygous for this condition. The typical characteristic clinical features in these subjects are as follows: (1) short hands with wrinkled fatty skin and short feet; (2) complete soft tissue syndactyly involving all four limbs; (3) polydactyly of the preaxial, mesoaxial, and postaxial digits of the hands; (4) loss of the normal tubular shape of the carpal, metacarpal, and phalangeal bones, so as to give polygonal structures; (5) loss of the typical structure of the cuboid and all three cuneiform bones while the talus calcaneus and navicular bones remain intact; (6) large bony islands instead of metatarsals, most probably because of cuboid-metatarsal and cuneiform-metatarsal fusions; and (7) severe middle phalangeal hypoplasia/aplasia as well as fusion of some phalangeal structures that are associated with the loss of normal phalangeal pattern. We report seven subjects with this phenotype from three different branches of a very large SPD pedigree exhibiting the same phenotype with minimal variation. In mice, the Polysyndactyly (Ps) mutation shows a pattern of synpolydactyly very similar to that of human SPD, suggesting that they may well be homologous mutations. A molecular genetic study is currently under way to determine the chromosomal location of the SPD locus in humans and to identify the corresponding homologous region in mice.

Absent tibiae--polydactyly--triphalangeal thumbs with fibular dimelia: variable expression of the Werner (McKusick 188770) syndrome?

We report on a family in which the autosomal dominant Werner syndrome (WS) (MIM# 188770) affects ten members in three generations. Besides the absent tibiae the propositus had duplication of the fibulae. Possible pathogenetic mechanism is discussed.

Alopecia areata in aging C3H/HeJ mice

A disease closely resembling human alopecia areata was found in a large production colony of C3H/HeJ mice that had no evidence of thyroid dysfunction or an infectious etiology. Alopecia developed diffusely or in circular areas on the dorsal surface. Histologically, the changes in this non-scarring alopecia were limited to anagen follicles that were surrounded by mononuclear cells. This infiltrate, composed primarily of cytotoxic (CD8+) and helper (CD4+) T cells, was associated with follicular and hair shaft dystrophy. This infiltrate was markedly reduced by intralesional injection of triamcinolone acetonide with subsequent hair regrowth in the affected site. Pedigree tracing of affected C3H/HeJ mice suggests that this non-scarring alopecia may be an inherited disease. Breeding results of normal haired mice with alopecia areata mice or between alopecia areata mice suggests that this is a complex polygenic disease with a female predominance at younger ages. Female mice developed the disease earlier than male mice (3-5 versus > 6 months), with equal numbers affected by 18 months of age. The relative incidence of alopecia areata in one production colony of C3H/HeJ mice was 0.25% for female and 0.035% for male mice, but selective breeding has raised the frequency to nearly 20%. The frequency in an aging colony selectively bred for inflammatory bowel disease reached 4.7%, with equal sex distribution, for mice over 18 months of age, suggesting that this might be a common aging change in C3H/HeJ mice. This C3H/HeJ mouse disease may prove to be a valuable animal model to study specific subtypes of human alopecia areata.

Dysmorphic disorders--an overview

Clinical delineation of dysmorphic syndromes is important for patient management, family counselling and basic research. Productive areas of research in dysmorphology and developmental biology have included the study of the mouse homologies of human disease. Mutations have been identified in both species in highly conserved 'developmental' genes, and also because of phenotypic similarity of syndromes. Mosaicism--somatic, germline and placental--involving chromosomal aneuploidy, single gene mutations and functional differences between cell lines is an important cause of malformations and syndromes. Many recurrent pattern malformation syndromes of previously unknown cause have now been found to be due to chromosomal microdeletions. Diagnosis has been greatly aided by the molecular cytogenetic technique of fluorescent in situ hybridization.

Mouse homologues of human hereditary disease

Details are given of 214 loci known to be associated with human hereditary disease, which have been mapped on both human and mouse chromosomes. Forty two of these have pathological variants in both species; in general the mouse variants are similar in their effects to the corresponding human ones, but exceptions include the Dmd/DMD and Hprt/HPRT mutations which cause little, if any, harm in mice. Possible reasons for phenotypic differences are discussed. In most pathological variants the gene product seems to be absent or greatly reduced in both species. The extensive data on conserved segments between human and mouse chromosomes are used to predict locations in the mouse of over 50 loci of medical interest which are mapped so far only on human chromosomes. In about 80% of these a fairly confident prediction can be made. Some likely homologies between mapped mouse loci and unmapped human ones are also given. Sixty six human and mouse proto-oncogene and growth factor gene homologies are also listed; those of confirmed location are all in known conserved segments. A survey of 18 mapped human disease loci and chromosome regions in which the manifestation or severity of pathological effects is thought to be the result of genomic imprinting shows that most of the homologous regions in the mouse are also associated with imprinting, especially those with homologues on human chromosomes 11p and 15q. Useful methods of accelerating the production of mouse models of human hereditary disease include (1) use of a supermutagen, such as ethylnitrosourea (ENU), (2) targeted mutagenesis involving ES cells, and (3) use of gene transfer techniques, with production of 'knockout mutations'.

Waardenburg syndrome in man and splotch mutants in the mouse: a paradigm of the usefulness of linkage and synteny homologies in mouse and man for the genetic analysis of human congenital malformations

The use of chromosomal segments with conserved homologous linkage groups found in different species provides one method of predicting the location of genes causing congenital malformations in man. For example, homology between man and mouse involves 241 homologous autosomal genes spread on 68 homologous chromosomal segments. In addition, the similarities of phenotypic expression of human congenital malformations and mouse mutations indicate the possible involvement of an homologous gene implicated during ontogeny of the two species. The identification of a single gene defect in the mouse and comparative mouse-human gene mapping provides therefore another approach for selecting candidate loci for inborn error of morphogenesis in man. Further molecular studies can then be performed to show that the loci are identical. The human Waardenburg syndrome and the splotch (Sp) mouse mutant represent the first example of the potential of this approach for the understanding of human congenital malformations at the molecular level.

Ionizing radiation, genetic risk estimation and molecular biology: impact and inferences

In recent years, a substantial amount of information has been obtained on the molecular nature of spontaneous mutations underlying human mendelian diseases, and on the mechanisms that give rise to these mutations. These data, when considered together with data on mutations induced by ionizing radiation in mammalian experimental systems, support the view that current radiation risk estimates for mendelian diseases (which are based on mouse data) are conservative.

Waardenburg syndrome and myelomeningocele in a family

We report the first family with Waardenburg syndrome type 1 and myelomeningocele in which more than one subject was affected with both disorders. The possible association is discussed. Prenatal screening for myelomeningocele is suggested for a family with Waardenburg syndrome type 1.

Mouse models of human single gene disorders. I: Nontransgenic mice

Mouse models of human genetic disorders provide a valuable resource for investigating the pathogenesis of genetic disease and for testing potential therapies. The high degree of resolution of linkage mapping in the mouse allows mutant phenotypes to be mapped precisely which, combined with the accurate definition of areas of homology between the mouse and human genomes, greatly facilitates the identification of mouse models. We describe here mouse models of human single gene disorders dividing them into three categories depending on the information available; phenotypic similarities, comparative mapping and identification of the underlying genetic lesion.

Waardenburg I syndrome: a clinical and genetic study of two large Brazilian kindreds, and literature review

Two large kindreds with Waardenburg I syndrome are described. The total number of affected individuals is 73. The major manifestations are telecanthus (the only constant anomaly in all cases), prominent nasal root, round or square tip of nose, hypoplastic alae, smooth philtrum, bushy eyebrows with synophrys, sensorineural deafness, heterochromia or hypoisochromia iridis, hypopigmented ocular fundus, white forelock, premature greying, and hypopigmented skin lesions. These and other aspects of the syndrome, associated findings, frequency, genetic heterogeneity, pathogenesis, animal models, and gene linkage and mapping are reviewed briefly.

Molecular characterization of a deletion encompassing the splotch mutation on mouse chromosome 1

We have used a set of markers newly assigned to the proximal portion of mouse chromosome 1 to characterize the chromosomal segment deleted in the splotch-retarded (Spr) mouse mutant. Among nine markers tested in the heterozygote Spr/+mouse, we have identified four genes, Vil, Des, Inha, and Akp-3, which map within the Spr deletion. The closest distal marker to the deletion is the Acrg gene, with the distal deletion breakpoint mapping within the 0.8-cM segment separating Akp-3 and Acrg. The most proximal gene to the Spr deletion is Tp1. The proximal deletion breakpoint maps within the 0.8-cM segment separating Tp1 and Vil. The minimum size of the Spr deletion would therefore be limited to 14 cM, the genetic distance between Vil and Akp-3. The maximum size of the Spr deletion is estimated to be 16 cM, the genetic distance between Tp1 and Acrg.

A human gene homologous to the formin gene residing at the murine limb deformity locus: chromosomal location and RFLPs

The murine limb deformity (ld) locus resides on mouse chromosome 2 and gives rise to a recessively inherited, characteristic limb deformity/renal aplasia phenotype. In this locus in the mouse, a gene, termed the "formin" gene, has been identified which encodes an array of differentially processed transcripts in both adult and embryonic tissues. A set of these transcripts are disrupted in independent mutant mouse ld alleles. We wish to report the isolation of a human genomic clone which is homologous to the mouse formin gene by virtue of sequence comparison and expression of conserved exons. Among human fetal tissues analyzed, the kidney appears to be a major site of expression. This human gene, LD, maps to chromosome 15q11----qter in mouse human somatic cell hybrids and, specifically, to 15q13----q14 by chromosomal in situ hybridization. This localization establishes both LD and beta 2-microglobulin as syntenic genes on mouse chromosome 2 and human chromosome 15 and implies the interspecies conservation of the region between them. In addition, we identify in the human locus two frequently occurring DNA polymorphisms which can be used to test the linkage of LD to known human dysmorphoses.

A genetic linkage map of mouse chromosome 10: localization of eighteen molecular markers using a single interspecific backcross

Interspecific mouse backcross analysis was used to generate a molecular genetic linkage map of mouse chromosome 10. The map locations of the Act-2, Ahi-1, Bcr, Braf, Cdc-2a, Col6a-1, Col6a-2, Cos-1, Esr, Fyn, Gli, Ifg, Igf-1, Myb, Pah, pgcha, Ros-1 and S100b loci were determined. These loci extend over 80% of the genetic length of the chromosome, providing molecular access to many regions of chromosome 10 for the first time. The locations of the genes mapped in this study extend the known regions of synteny between mouse chromosome 10 and human chromosomes 6, 10, 12 and 21, and reveal a novel homology segment between mouse chromosome 10 and human chromosome 22. Several loci may lie close to, or correspond to, known mutations. Preferential transmission of Mus spretus-derived alleles was observed for loci mapping to the central region of mouse chromosome 10.

A molecular genetic linkage map of mouse chromosome 13 anchored by the beige (bg) and satin (sa) loci

A molecular genetic linkage map of mouse chromosome 13 was constructed using cloned DNA markers and interspecific backcross mice from two independent crosses. The map locations of Ctla-3, Dhfr, Fim-1, 4/12, Hexb, Hilda, Inhba, Lamb-1.13, Ral, Rrm2-ps3, and Tcrg were determined with respect to the beige (bg) and satin (sa) loci. The map locations of these genes confirm and extend regions of homology between mouse chromosome 13 and human chromosomes 5 and 7, and identify a region of homology between mouse chromosome 13 and human chromosome 6. The molecular genetic linkage map of chromosome 13 provides a framework for establishing linkage relationships between cloned DNA markers and known mouse mutations and for identifying homologous genes in mice and humans that may be involved in disease processes.

Chromosome maps of man and mouse. IV

Current knowledge of man-mouse genetic homology is presented in the form of chromosomal displays, tables and a grid, which show locations of the 322 loci now assigned to chromosomes in both species, as well as 12 DNA segments not yet associated with gene loci. At least 50 conserved autosomal segments with two or more loci have been identified, twelve of which are over 20 cM long in the mouse, as well as five conserved segments on the X chromosome. All human and mouse chromosomes now have conserved regions; human 17 still shows the least evidence of rearrangement, with a single long conserved segment which apparently spans the centromere. The loci include 102 which are known to be associated with human hereditary disease; these are listed separately. Human parental effects which may well be the result of genomic imprinting are reviewed and the location of the factors concerned displayed in relation to mouse chromosomal regions which have been implicated in imprinting phenomena.

Maps of linkage and synteny homologies between mouse and man

The recent introduction of biochemical and molecular methods for characterizing and mapping genes has dramatically increased the number of homologous genes that have been mapped in more than one species. This review assesses the status of the map of genes whose chromosomal locations have been determined in both mouse and man, evaluates progress towards saturated maps, and illustrates the manner in which this information is now being used in fields as diverse as medical and evolutionary genetics.