Chromosomal localisation of a pseudoautosomal growth gene(s)

Steroid-resistant nephrotic syndrome associated with steroid sulfatase deficiency-x-linked recessive ichthyosis: a case report and review of literature

Nephrotic syndrome associated with X-linked recessive ichthyosis due to steroid sulfatase deficiency has rarely been reported in English literature. We describe a 4 and a half-year-old boy presenting with steroid-resistant nephrotic syndrome (SRNS) with an underlying ichthyotic skin present since birth. Renal biopsy revealed minimal change disease. As many of the male members of the family also showed similar skin manifestations, genetic analysis was done on the patient, which revealed deletion of the steroid sulfatase (STS) gene spanning both the 3' as well as the 5'ends. The patient was thus diagnosed with SRNS associated with X-linked recessive ichthyosis. He was started on cyclosporine regimen, and remission was achieved in 5 weeks. We speculate that the deficiency of STS resulting in increased cholesterol sulfate accumulation interferes with the integrity of adherens junctions present between glomerular epithelial cells of the slit diaphragm, and this results in proteinuria and nephrotic syndrome. The nephrotic syndrome remitted with a calcineurin inhibitor medication.

CONCLUSION

We suggest that the deficiency of STS is another one in an increasing list of genetic causes of podocytopathy and nephrotic syndrome. Remission of proteinuria in such a case may be achieved with immunosuppressive medication.

Sex Differences in Genetic and Environmental Factors Contributing to Body-Height

Sex differences in the heritability of self-reported body-height in two Finnish twin cohorts were studied by using sex-limitation models. The first cohort was born in 1938–1949 (N = 4873 twin pairs) and the second in 1975–1979 (N = 2374 twin pairs). Body-height was greater in the younger cohort (difference of 3.1 cm for men and 2.9 cm for women). The heritability estimates were higher among men (h2 = 0.87 in the older cohort and h2 = 0.82 in the younger cohort) than women (h2 = 0.78 and h2 = 0.67, respectively). Sex-specific genetic factors were not statistically significant in either cohort, suggesting that the same genes contribute to variation in body height for both men and women. The stronger contribution of environmental factors to body-height among women questions the hypothesis that women are better buffered against environmental stress, at least for this phenotype.

Genes and phenotypes of the human Y chromosome

By 1959 it was recognized that the gene (or genes) responsible for initiating the human male phenotype were carried on the Y chromosome. But in subsequent years, few phenotypes were associated with the Y chromosome. Recently, using molecular techniques combined with classical genetics, the Y chromosome has been the focus of intensive and productive investigation. Some of the findings are unexpected and have extended our understanding of the functions of the human Y chromosome. The notion that the Y chromosome is largely devoid of genes is changing. At the present, over 20 Y chromosome genes or pseudogenes have been identified or cloned, a number that is rapidly increasing. A high proportion of Y chromosome sequences have been found to be related to X chromosome sequences: the assembly of a complete physical map of the Y chromosome euchromatic region (believed to carry all of the genes) has shown 25% of the region studied to have homology to the X chromosome.3 Several X-homologous genes are located in the X and Y chromosome pairing regions, an area predicted to have shared homology. Surprisingly, some of the Y-encoded genes that lie outside of the X and Y pairing region share high sequence similarity, and in at least one case, functional identity, with genes on the X chromosome.

Cognition and the sex chromosomes: studies in Turner syndrome

Turner syndrome (TS) is a human genetic disorder involving females who lack all or part of one X chromosome. The complex phenotype includes ovarian failure, a characteristic neurocognitive profile and typical physical features. TS features are associated not only with complete monosomy X but also with partial deletions of either the short (Xp) or long (Xq) arm (partial monosomy X). Impaired visual-spatial/perceptual abilities are characteristic of TS children and adults of varying races and socioeconomic status, but global developmental delay is uncommon. The cognitive phenotype generally includes normal verbal function with relatively impaired visual-spatial ability, attention, working memory, and spatially dependent executive function. The constellation of neurocognitive deficits observed in TS is most likely multifactorial and related to a complex interaction between genetic abnormalities and hormonal deficiencies. Furthermore, other determinants, including an additional genetic mechanism, imprinting, may also contribute to cognitive deficits associated with monosomy X. As a relatively common genetic disorder with well-defined manifestations, TS presents an opportunity to investigate genetic and hormonal factors that influence female cognitive development. TS is an excellent model for such studies because of its prevalence, the well-characterized phenotype, and the wealth of molecular resources available for the X chromosome. In the current review, we summarize the hormonal and genetic factors that may contribute to the TS neurocognitive phenotype. The hormonal determinants of cognition in TS are related to estrogen and androgen deficiency. Our genetic hypothesis is that haploinsufficiency for gene/genes on the short arm of the X chromosome (Xp) is responsible for the hallmark features of the TS cognitive phenotype. Careful clinical and molecular characterization of adult subjects missing part of Xp links the TS phenotype of impaired visual spatial/perceptual ability to specific distal Xp chromosome regions. We demonstrate that small, nonmosaic deletion of the distal short arm of the X chromosome in adult women is associated with the same hallmark cognitive profile seen in adult women with TS. Future studies will elucidate the cognitive deficits and the underlying etiology. These results should allow us to begin to design cognitive interventions that might lessen those deficits in the TS population.

Molecular and cytogenetic analysis of familial Xp deletions

Five families in which an Xp deletion is segregating and two families in which an X chromosome rearrangement including a deletion of the short arm is segregating were ascertained for study. Normal fertility was seen in all families. Members from 5 of the 7 families manifested short stature (height <5th centile), while normal height was present in two families. Studies of both the FMR-1 and the androgen receptor loci using PCR based X-inactivation analysis demonstrated that in all families analyzed, there is preferential inactivation of one X chromosome. Molecular cytogenetic analysis showed that members of 3 of the 7 families share a common breakpoint in an approximate 2-3 Mb region at Xp22.12, suggesting a possible hotspot for chromatin breakage. Previous genotype-phenotype correlations and deletion mapping have indicated that a gene for stature resides within the pseudoautosomal region in Xp22.33. Our findings indicate that the loss of this region is not always associated with short stature, suggesting that other factors may be involved.

SHOX gene mutations and deletions in dyschondrosteosis or Leri-Weill syndrome

Dyschondrosteosis is an autosomal dominant form of mesomelic dysplasia that is often combined with a deformity of the forearms called Madelung deformity. Based on the observation of X-Y translocations (p22,q12) in patients with dyschondrosteosis, the authors tested the pseudoautosomal region in eight affected families and showed linkage of the dyschondrosteosis gene to a microsatellite DNA marker at the DXYS233 locus (Zmax = 6.26 at theta = 0). Since the short stature homeobox-containing gene (SHOX) involved in idiopathic growth retardation and possibly Turner syndrome maps to this region, SHOX was regarded as a strong candidate gene for dyschondrosteosis. This article reports the detection of large-scale SHOX deletions in seven of the eight families and a nonsense mutation of SHOX in the remaining family affected with dyschondrosteosis. Additional evidence suggests that Langer mesomelic dwarfism results from homozygous mutations at the genetic locus responsible for dyschondrosteosis.

X-linked ichthyosis: an update

X-linked ichthyosis is a genetic disorder of keratinization characterized by a generalized desquamation of large, adherent, dark brown scales. Extracutaneous manifestations include corneal opacity and cryptorchidism. Since 1978 it has been known that a deficit in steroid sulphatase enzyme (STS) is responsible for the abnormal cutaneous scaling, although the exact physiological mechanism remains uncertain. The STS gene has been mapped to the distal part of the short arm of the X chromosome. Interestingly, this region escapes X chromosome inactivation and has the highest ratio of chromosomal deletions among all genetic disorders, complete deletions having been found in up to 90% of patients. Diagnosis of patients with X-linked ichthyosis and female carriers is based on biochemical and genetic analysis. The latter currently seems to be the most accurate method in the majority of cases.

Schizophrenia susceptibility gene locus at Xp22.3

Multiple genetic loci have been implicated in the search for schizophrenia susceptibility genes, none having been proven as causal. Genetic heterogeneity is probable in the polygenic etiology of schizophrenia. We report on two unrelated Caucasian women with paranoid schizophrenia (meeting Diagnostic and Statistical Manual of Mental Disorders (DSM IV) criteria) who have an Xp22.3 overlapping deletion characterized by fluorescence in situ hybridization (FISH). Patient 1 was previously reported by us (Wyandt HE, Bugeau-Michaud L, Skare JC, Milunsky A. Partial duplication of Xp: a case report and review of previously reported cases. Amer J Med Genet 1991: 40: 280-283) to have a de novo partial duplication of Xp. At that time, she was a 24-year-old woman with short stature, irregular menses, other abnormalities suggestive of Turner syndrome, and paranoid schizophrenia. Recently, FISH analysis demonstrated that she has an inverted duplication (X)(p22.1p11.2) and a microscopic deletion (X)(p22.2p22.3) between DXS1233 and DXS7108 spanning approximately 16-18 cM. Patient 2 is a 14-year-old girl with short stature, learning disabilities, and paranoid schizophrenia. High-resolution chromosome analysis revealed a de novo deletion involving Xp22. FISH analysis showed that the deletion (X)(p22.2p22.3) spanned 10-12 cM between AFMB290XG5 and DXS1060. Given that deletions of Xp22 are not common events, the occurrence of two unrelated schizophrenia patients with an overlapping deletion of this region would be extraordinarily rare. Hence, the deletion within Xp22.3 almost certainly contains a gene involved in the pathogenesis of paranoid schizophrenia.

Evidence for a Turner syndrome locus or loci at Xp11.2-p22.1

Turner syndrome is the complex human phenotype associated with complete or partial monosomy X. Principle features of Turner syndrome include short stature, ovarian failure, and a variety of other anatomic and physiological abnormalities, such as webbed neck, lymphedema, cardiovascular and renal anomalies, hypertension, and autoimmune thyroid disease. We studied 28 apparently nonmosaic subjects with partial deletions of Xp, in order to map loci responsible for various components of the Turner syndrome phenotype. Subjects were carefully evaluated for the presence or absence of Turner syndrome features, and their deletions were mapped by FISH with a panel of Xp markers. Using a statistical method to examine genotype/phenotype correlations, we mapped one or more Turner syndrome traits to a critical region in Xp11.2-p22.1. These traits included short stature, ovarian failure, high-arched palate, and autoimmune thyroid disease. The results are useful for genetic counseling of individuals with partial monosomy X. Study of additional subjects should refine the localization of Turner syndrome loci and provide a rational basis for exploration of candidate genes.

SHOX mutations in dyschondrosteosis (Leri-Weill syndrome)

Dyschondrosteosis (DCS) is an autosomal dominant form of mesomelic dysplasia with deformity of the forearm (Madelung deformity; ref. 3). Based on the observation of XY translocations (p22,q12; refs 4-6) in DCS patients, we tested the pseudoautosomal region in eight families with DCS and showed linkage of the DCS gene to a microsatellite DNA marker at the DXYS233 locus (Zmax=6.26 at theta=0). The short stature homeobox-containing gene (SHOX), involved in idiopathic growth retardation and possibly Turner short stature, maps to this region and was therefore regarded as a strong candidate gene in DCS. Here, we report large-scale deletions (in seven families) and a nonsense mutation (in one family) of SHOX in patients with DCS and show that Langer mesomelic dwarfism results from homozygous mutations at the DCS locus.

Del (X)(p21.2) in a mother and two daughters with variable ovarian function

We report a family in which a woman with the mosaic karyotype 45,X/46,X,del(X)(p21.2) transmitted the deleted X chromosome to two daughters. The nature of the deletion was confirmed by fluorescent in situ hybridization (FISH). All three family members showed somatic Ullrich-Turner syndrome features, but only one daughter had ovarian failure. These observations have implications for the diagnosis of Ullrich-Turner syndrome and genotype/phenotype correlations of X chromosome deletions.

Presence of Turner stigmata in a case of dysgenetic male pseudohermaphroditism with 45,X/46,X+mar karyotype

A case is reported of dysgenetic male pseudohermaphroditism (DMPH) having Turner stigmata and 45,X/46,X+mar karyotype. The marker chromosome of this patient consisted of most if not all of the short arm, including the sex determining region of the Y chromosome. Although this karyotype is relatively common in Turner's syndrome and occasionally observed in mixed gonadal dysgenesis, DMPH is usually exemplified by a 46,XY karyotype except for one patient reported with 45,X/46,XY mosaicism. Turner stigmata have not previously been reported in DMPH. The present patient is an intermediate case between mixed gonodal dysgenesis and typical DMPH, and this indicates that 45,X/ 46,X +mar karyotype abnormality can result in a wide range of phenotype such as DMPH, mixed gonodal dysgenesis and Turner's syndrome.

Isochromosome Xq in Klinefelter syndrome: report of 7 new cases

In this collaborative study we report on 2 prenatally and 5 postnatally diagnosed cases with a 47,X,i(Xq),Y chromosomal constitution. Excepting tall stature, the 5 adult patients showed all typical manifestations of Klinefelter syndrome. Taken together with previously reported cases, these data suggest that Klinefelter syndrome with isochromosome Xq has a favorable prognosis with normal mental development, and with normal-to-short stature. The prevalence of this Klinefelter variant is calculated to be between 0.3-0.9% in males with X chromosome polysomies.

Mental retardation in a boy with an interstitial deletion at Xp22.3 involving STS, KAL1, and OA1: implication for the MRX locus

Although genotype-phenotype correlations in male patients with various types of nullisomy for Xp22.3 have assigned a locus for X-linked mental retardation (MRX) to an approximately 3-Mb region between DXS31 and STS, the precise location has not been determined. In this paper, we describe a 14 7/12 year old Japanese boy with mental retardation and an interstitial deletion at Xp22.3 involving STS, KAL1, and OA1, and compare the deletion map with that of previously reported three familial male patients with low-normal intelligence and a similar interstitial deletion at Xp22.3. The results suggest that the MRX gene is further localized to the roughly 1.5-Mb region between DXS1060 and DXS1139.

Familial X-linked mental retardation and isolated growth hormone deficiency: clinical and molecular findings

We report on several members of a family with varying degrees of X-linked mental retardation (XLMR), isolated growth hormone deficiency (IGHD), and infantile behaviour but without other consistent phenotypic abnormalities. Male patients continued to grow until well into their twenties and reached a height ranging from 135 to 159 cm. Except one, all female carriers were mentally normal; their adult height ranged from 159 to 168 cm. By linkage studies we have assigned the underlying genetic defect to the Xq24-q27.3 region, with a maximum lod score of Z = 3.26 at theta = 0.0 for the DXS294 locus. The XLMR-IGHD phenotype in these patients may be due to pleiotropic effects of a single gene or it may represent a contiguous gene syndrome.

Short stature in a mother and daughter with terminal deletion of Xp22.3

Short stature in females is often caused by hemizygosity for the terminal portion of Xp due to monosomy X or a deletion. We report on a mother and daughter with short stature as sole phenotypic abnormality and deletion of bands Xp22.32-p22.33 demonstrated by classic and molecular cytogenetic analysis. In both individuals, the deleted X chromosome was late replicating. Molecular analysis suggested that the deletion is terminal and the breakpoint was localized between the STS and DXS7470 loci in Xp22.32. Chromosome analysis is often done on females with short stature to exclude Ullrich-Turner syndrome. Small deletions, terminal or interstitial, are easily missed by conventional cytogenetic investigation; thus molecular analyses are useful to detect those cases.

Distribution of marker-Y chromosome containing cells in different tissues of a Turner mosaic patient with mixed gonadal dysgenesis

We here describe a 12-year-old girl with numerous Turner stigmata and virilized external genitalia. Chromosome analysis of PHA stimulated lymphocytes using different banding techniques revealed a 45,X/46,X,+mar Turner mosaicism with the prominent marker present in about 90% of the blood cells. A PCR-based analysis using a set of 9 STS from different regions of the human Y chromosome indicated the presence of Y chromosomal material with a deletion breakpoint most likely within deletion interval 6. Because of the risk of gonadoblastoma for Turner patients carrying Y chromosomal material, and clinical indications of functional testicular tissue, a gonadectomy in addition to surgical correction of the external genitalia was performed. The histological analysis of the gonads showed a mixture of testicular tissue and ovarian stroma, thus indicating mixed gonadal dysgenesis. Fibroblasts from skin and different parts of the gonads were cytogenetically analyzed and showed a variable distribution of the Y-derived marker between 4% in skin, 11-31% in gonadal tissue and up to 90% in peripheral lymphocytes.

An analysis of Xq deletions

We characterized by fluorescence in situ hybridization and Southern blotting 14 partial Xq monosomies, 11 due to terminal deletions and 3 secondary to X/autosome translocations. Three cases were mosaics with a XO cell line. In view of the possible role played by telomeres in chromosome segregation, we hypothesize a relationship between the loss of telomeric sequences in terminal deletions and the presence of 45,X cells. A correlation between phenotype and extent of deletion reveal that there is no correspondence between the size of the deletion and impairment of gonadal function. Turner stigmata are absent in patients without an XO cell line, when the breakpoint is distal to Xq24. A low birthweight is present whenever the breakpoint is at q22 or more proximal.

Short stature in a girl with partial monosomy of the pseudoautosomal region distal to DXYS15: further evidence for the assignment of the critical region for a pseudoautosomal growth gene(s)

This report describes a 12 year 10 month old girl with short stature and a non-mosaic 46,X,Xp+ karyotype. Her height remained below −2 SD of the mean, and her predicted adult height (143 cm) was below her target height (155·5 cm) and target range (147·5 cm−163·5 cm). Cytogenetic and molecular studies showed that the Xp+ chromosome was formed by an inverted duplication of the Xp21.3−Xp22.33 segment and was missing about 700 kb of DNA from the pseudoautosomal region distal to DXYS15. The results provide further support for the previously proposed hypothesis that the region between DXYS20 and DXYS15 is the critical region for a pseudoautosomal growth gene(s).

Chromosomal localisation of a Y specific growth gene(s)

Although a Y specific growth gene(s) has been postulated in the Yq11 region, the precise location has not been determined. To localise the growth gene(s), we correlated genotype with stature in 13 Japanese and four European non-mosaic adult male patients with a partial Yq deletion. Fourteen patients preserving the region between DYS11 and DYS246 did not have short stature (11 Japanese, 165-180 cm; three Europeans, 165-173 cm) whereas the remaining three patients with the region deleted had short stature (two Japanese, both 159 cm; one European, 157 cm). The results suggest that the region defined by DYS11 at interval 5C and by DYS246 at interval 5D may be the critical region for the Y specific growth gene(s).

SRY alone can induce normal male sexual differentiation

Most individuals with the rare 46,XX male "syndrome" arise due to an unequal interchange between Xp and Yp termini during paternal meiosis. The pattern of Y-sequences in these patients varies considerably, but very few cases have been reported showing only SRY. The phenotype in these patients is also variable ranging from severe impairment of the external genitalia through hypospadias and/or cryptorchidism to occasional normal male phenotype. We report a Mexican 46,XX male patient without genital ambiguities in whom DNA analysis showed the presence of SRY and the absence of ZFY. We conclude that in this case SRY alone was enough for complete male sexual differentiation.

Development and physical analysis of YAC contigs covering 7 Mb of Xp22.3-p22.2

A total of 54 YAC clones have been isolated from the region of Xp22.2-p22.3 extending from the amelogenin gene locus to DXS31. Restriction analysis of these clones in association with STS contenting and end clone analysis has facilitated the construction of 6 contigs covering a total of 7 Mb in which 20 potential CpG islands have been located. Thirty new STSs have been developed from probe and YAC end clone sequences, and these have been used in the analysis of patients suffering from different combinations of chondrodysplasia punctata, mental retardation, X-linked ichthyosis, and Kallmann syndrome. The results suggest that (1) the gene for chondrodysplasia punctata must lie between the X chromosome pseudoautosomal boundary (PABX) and DXS1145; (2) a gene for mental retardation lies between DXS1145 and the sequence tagged site GS1; and (3) the gene for ocular albinism type 1 lies proximal to the STS G13. The CpG islands within the YAC contigs constitute valuable markers for the potential positions of genes. Genes found associated with any of these potential CpG islands would be possible candidates for the disease genes mentioned above.

Deletions of Xq and growth deficit: a review

A critical review of the literature disclosed 44 cases with a 46,X,Xq- karyotype without apparent mosaicism. Of these, 17 were of normal height (compared to the respective population), 11 had a height of over 1 SD below the mean, and 16 had a height of over 2 SD below the mean with breakpoints between Xq13 and Xq25. Since patients of normal height occurred with breakpoints as proximal as Xq13 we conclude that there is no major "growth gene" on Xq distal to q13. The most likely explanation for the variable phenotypic effect of Xq- is to assume that growth gene(s) in Xp or proximal Xq are inactivated on such a chromosome with some variability similar to the variable spreading of X inactivation seen in some X-autosome translocations.

Chromosomal localisation of a gene(s) for Turner stigmata on Yp

Although recent cytogenetic and molecular studies in patients with Turner stigmata are consistent with a gene(s) for Turner stigmata being present on both Xp and Yp, the precise location has not been determined. In this report, we describe a phenotypically female infant with Turner stigmata and a partial Yp deletion and review genotype-phenotype correlations of the putative Turner gene(s) in non-mosaic patients with Y chromosome rearrangements resulting from chromosomal breakage at Yp or Yc (pericentromeric region). The results indicate that the putative Turner gene(s) on Yp is located in the Y specific region from interval 1A1A to interval 2B. In addition, assessment of ZFX/ZFY and RPS4X/RPS4Y in the context of the Turner gene(s) suggests that ZFX/ZFY rather than RPS4X/RPS4Y could be a candidate gene for the Turner stigmata.

The pseudoautosomal regions of the human sex chromosomes

In human females, both X chromosomes are equivalent in size and genetic content, and pairing and recombination can theoretically occur anywhere along their entire length. In human males, however, only small regions of sequence identity exist between the sex chromosomes. Recombination and genetic exchange is restricted to these regions of identity, which cover 2.6 and 0.4 Mbp, respectively, and are located at the tips of the short and the long arm of the X and Y chromosome. The unique biology of these regions has attracted considerable interest, and complete long-range restriction maps as well as comprehensive physical maps of overlapping YAC clones are already available. A dense genetic linkage map has disclosed a high rate of recombination at the short arm telomere. A consequence of the obligatory recombination within the pseudoautosomal region is that genes show only partial sex linkage. Pseudoautosomal genes are also predicted to escape X-inactivation, thus guaranteeing an equal dosage of expressed sequences between the X and Y chromosomes. Gene pairs that are active on the X and Y chromosomes are suggested as candidates for the phenotypes seen in numerical X chromosome disorders, such as Klinefelter's (47,XXY) and Turner's syndrome (45,X). Several new genes have been assigned to the Xp/Yp pseudoautosomal region. Potential associations with clinical disorders such as short stature, one of the Turner features, and psychiatric diseases are discussed. Genes in the Xq/Yq pseudoautosomal region have not been identified to date.

Analysis of a terminal Xp22.3 deletion in a patient with six monogenic disorders: implications for the mapping of X linked ocular albinism

The molecular characterisation of chromosomal aberrations in Xp22.3 has established the map position of several genes with mutations resulting in diverse phenotypes such as short stature (SS), chondrodysplasia punctata (CDPX), mental retardation (MRX), ichthyosis (XLI), and Kallmann syndrome (KAL). We describe the clinical symptoms of a patient with a complex syndrome compatible with all these conditions plus ocular albinism (OA1). He has a terminal Xp deletion of at least 10 Mb of DNA. Both the mother and sister of the patient are carriers of the deletion and show a number of traits seen in Turner's syndrome. The diagnosis of ocular albinism was confirmed in the patient and his mother, who shows iris translucency, patches and streaks of hypopigmentation in the fundus, and macromelanosomes in epidermal melanocytes. By comparative deletion mapping we can define a deletion interval, which locates the OA1 gene proximal to DXS143 and distal to DXS85, with the breakpoints providing valuable starting points for cloning strategies.

Sex chromosome aberrations and stature: deduction of the principal factors involved in the determination of adult height

Although sex chromosome aberrations are frequently associated with statural changes, the underlying factors have not been clarified. To define the factors leading to the statural changes, we took the following three steps: (1) determination of the mean adult height in nonmosaic Caucasian patients with sex chromosome aberrations reported in the literature (assessment of genetic height potential); (2) assessment of the validity of factors that could influence stature; and (3) correlation of the mean adult height with the effects of specific growth-related factors. The results indicate that the adult height in patients with sex chromosome aberrations may primarily be defined by the dosage effect of pseudoautosomal and Y-specific growth genes, together with the degree of growth disadvantage caused by alteration of the quantity of euchromatic or non-inactivated region.