X/Y translocation in a family with X-linked ichthyosis, chondrodysplasia punctata, and mental retardation: DNA analysis reveals deletion of the steroid sulphatase gene and translocation of its Y pseudogene

Xp;Yq Unbalanced Translocation with Pseudoautosomal Region Aberrations in a Natural Two-Generation Transmission

Translocations involving X and Y chromosomes rarely occur in humans and may affect reproductive function. We investigated an Xp:Yq unbalanced translocation with pseudoautosomal region (PAR) aberrations in a natural two-generation transmission. We report the case of an azoospermic male and his fertile mother without any other abnormal clinical phenotypes, except for short stature. Cytogenetic methods, including karyotyping and fluorescence in situ hybridization (FISH), revealed the translocation. Chromosomal microarray comparative genomic hybridization (array-CGH) was used to investigate the regions of Xp partial deletion and Yq partial duplication. Final chromosome karyotypes in the peripheral blood of the infertile male and his mother were 46,Y,der(X)t(X;Y)(p22.33;q11.22) and 46,X,der(X)t(X;Y)(p22.33;q11.22), respectively. Short-stature-homeobox gene deletion was responsible for the short stature in both subjects. PAR aberrations and AZFc duplication may be a direct genetic risk factor for spermatogenesis. This report further supports the use of routine karyotype analysis, FISH-based technology, and array-CGH analysis to identify derivative chromosomes in a complex rearrangement.

Unique karyotype: mos 46,X,dic(X;Y)(p22.33;p11.32)/ 45,X/45,dic(X;Y)(p22.33;p11.32) in an Egyptian patient with Ovotesticular disorder of sexual development

Ovotesticular disorder of sexual development (OT-DSD) is an unusual form of DSD, characterized by the coexistence of testicular and ovarian tissue in the same individual. In this report, we present clinical, cytogenetic and molecular data of an Egyptian patient with ambiguous genitalia and OT-DSD, who had a unique karyotype comprising 3 different cell lines: mos 46,X,dic(X;Y)(p22.33;p11.32)/45,X/ 45,dic(X;Y)(p22.33;p11.32). This mosaic karyotype probably represents 2 different events: abnormal recombination between the X and Y chromosomes during paternal meiosis and postzygotic abnormality in mitotic segregation of the dic(X;Y) chromosome, resulting in a mosaic karyotype. The presence of the sex-determining region Y (SRY) gene explains the development of testicular tissue. On the other hand, other factors, including the presence of a 45,X cell line, partial SRY deletion, X inactivation pattern, and position effect, could be contributed to genital ambiguity. Explanation of the patient's phenotype in relation to the genotype is discussed with a literature review. We conclude that FISH analysis with X- and Y-specific probes and molecular analysis of the SRY gene are highly recommended and allow accurate diagnosis for optimal management of cases with ambiguous genitalia.

Karyotype determination and reproductive guidance for short stature women with a hidden Y chromosome fragment

Two unrelated couples came to the Reproductive and Genetic Hospital of Citic-Xiangya to ask for reproductive guidance. One couple had an affected son and the other couple had secondary infertility. Conventional GTG banding showed that the women in both couples had a 46,X,add(X)(p22) karyotype. Further molecular cytogenetic studies showed that both women had a 46,X,der(X)t(X;Y)(p22;q11.2) karyotype and that the affected boy had inherited the derivative X chromosome, which resulted in an Xp contiguous gene syndrome. After an assessment of reproductive risk, the first couple conceived naturally and opted for prenatal diagnosis (PND) by amniocentesis. No abnormal karyotypes were found for the twin pregnancy and healthy twin girls were born after a full-term normal pregnancy. The second couple chose to undergo IVF with preimplantation genetic diagnosis (PGD). Two PGD cycles were performed by fluorescence in-situ hybridization. In the first PGD cycle, all three embryos had abnormal hybridization signals. In the second cycle, a male embryo with normal hybridization signals was transferred into the womb and a normal pregnancy was achieved. The results show the importance of detecting the derivative chromosome followed by PND or PGD if a woman carries an Xp;Yq translocation.

Prenatal findings in a fetus with contiguous gene syndrome caused by deletion of Xp22.3 that includes locus for X-linked recessive type of chondrodysplasia punctata (CDPX1)

The X-linked recessive type of chondrodysplasia punctata (CDPX1) is a skeletal disorder that is characterized by stippled calcification at an epiphyseal nucleus and the surrounding soft tissue, short stature and an unusual face because of nasal hypoplasia. In most of the patients, this condition is noted after birth because of a characteristic face or respiratory problems. Here, we report a fetus with CDPX1. Two-dimensional ultrasound examination revealed unexplained polyhydramnios and a male fetus. Fetal biometry showed shortened long bones. Three-dimensional ultrasonography clearly demonstrated a hypoplastic nose with a depressed nasal bridge and contracture of wrists and fingers. Chromosome analysis of the amniotic fluid cells revealed the 46,Y,del(X)(p22.3) karyotype. Fluorescence in situ hybridization revealed a deletion of subtelomeric sequences at the Xpter and STS gene, but not a deletion of the KAL gene. The genomic copy number analysis demonstrated terminal deletion of 8.33 Mb that included SHOX, CSF2RA, XG, ARSE, NLGN4 and STS genes. We think that our case presents typical features of a fetus with this disorder and will be of great help in prenatal ultrasound diagnosis.

Chondrodysplasia punctata: a clinical diagnostic and radiological review

Chondrodysplasia punctata (CDP) is associated with a number of disorders, including inborn errors of metabolism, involving peroxisomal and cholesterol pathways, embryopathy and chromosomal abnormalities. Several classification systems of the different types of CDP have been suggested earlier. More recently, the biochemical and molecular basis of a number of CDP syndromes has recently been elucidated and a new aetiological classification has emerged. Here we provide an updated version with an overview of the different types of CDP, a discussion of the aetiology and a description of the clinical and radiographic findings. An investigative guideline to help determine the exact diagnosis in new cases is also presented.

GS2 as a retinol transacylase and as a catalytic dyad independent regulator of retinylester accretion

GS2 (PNPLA4; iPLAeta) is the smallest member of the patatin-like family of phospholipases (PNPLA). It was initially identified by its ability to hydrolyze retinylesters (RE) in cell homogenates, and was later found to esterify retinol using a variety of acyl donors. In the present study we set out to determine its cellular function and examined its impact on RE status in 293T cells transfected with GS2, GS2-M1 (a non-translatable mutant of GS2) and empty vector, in fibroblasts isolated from normal and GS2-null donors and in SCC12b and in a somatic cell knock-out of GS2 (SCC12b-GS2(neo/-)), that we generated by homologous recombination. At 50nM medium retinol, GS2 had no significant impact on RE accumulation. However, at 2muM retinol, GS2 promoted a 1.6- to 5-fold increase in RE accumulation. To verify role of GS2 as a catalyst, RE levels were measured in 293T transfected wild type GS2, catalytic dyad mutants devoid of enzymatic activity, or alanine substitution mutants spanning the entire GS2 sequence. Surprisingly, every GS2 mutant promoted RE accumulation. This activity was also observed in the GS2 paralogues and rat orthologue. The data demonstrate that within the context of the cell GS2 promotes RE accumulation and may do so either as a catalyst or as a regulatory protein that enhances RE formation catalyzed by other acyl transferases.

Steroid sulfatase deficiency with bilateral periventricular nodular heterotopia

This report presents a case of steroid sulfatase deficiency with bilateral periventricular nodular heterotopia. A 13-year-old male was diagnosed as having steroid sulfatase deficiency because steroid sulfatase activity was not detected in his leukocytes. In deoxyribonucleic acid studies, steroid sulfatase locus and adjacent loci were found to be deleted in his deoxyribonucleic acid. Cranial magnetic resonance imaging revealed periventricular nodular heterotopia, disclosing an irregular contour of the lateral walls of the lateral ventricles due to small nodular masses that were isointense as to the gray matter. In steroid sulfatase deficiency patients, bilateral periventricular nodular heterotopia must be considered.

An Xp; Yq translocation causing a novel contiguous gene syndrome in brothers with generalized epilepsy, ichthyosis, and attention deficits

PURPOSE

We describe two brothers with generalized epilepsy, attention deficits, congenital ichthyosis, and Leri-Weill dyschondrosteosis who harbor an unusual Xp; Yq translocation chromosome, resulting in a novel contiguous gene syndrome because of deletion of genes from the distal short arm of the X chromosome.

METHODS

Physical examination, neuropsychologic testing, EEG, and neuroimaging studies were performed. Because of their unusual phenotype, karyotyping, fluorescence in situ hybridization, and further molecular analyses were carried out to refine the break points of the underlying unbalanced sex chromosome rearrangement.

RESULTS

The subjects had generalized epilepsy, X-linked ichthyosis, Madelung deformities, mesomelia, normal intelligence, and attention deficits. The brothers' karyotype was unbalanced; they inherited a maternal derivative X chromosome. Deleted distal Xp genes included short-stature homeobox on the X chromosome (SHOX), aryl sulfatase E (ARSE), variably charged X-chromosome mRNA gene A (VCX-A), and steroid sulfatase (STS). The final karyotype was 46,Y,der(X)t(X; Y)(p22.3; q11.2).ish der(X) (DXZ1+, KAL+, STS-, SHOX-) mat.

CONCLUSIONS

Loss of distal contiguous Xp genes resulted in a syndrome comprising bony deformities, ichthyosis, attention problems, and generalized epilepsy. Candidate epilepsy genes within the deleted segment, such as ASMT, a gene involved in the final synthesis of melatonin, are discussed. Cytogenetic analyses should be included in the clinical evaluation of patients with generalized epilepsy and complex phenotypes.

X-linked recessive chondrodysplasia punctata: spectrum of arylsulfatase E gene mutations and expanded clinical variability

X-linked chondrodysplasia punctata (CDPX1), due to mutations of the arylsulfatase E (ARSE) gene, is a congenital disorder characterized by abnormalities in cartilage and bone development. We performed mutational analysis of the ARSE gene in a series of 16 male patients, and we found mutations in 12 subjects. Clinical variability was observed among the patients, including severe presentations with early lethality in one of them, and symptoms such as cataract and respiratory distress. This indicates that the clinical spectrum of CDPX1, commonly considered a relatively mild form of chondrodysplasia punctata, is wider than previously reported. Different types of mutations were found among the patients examined. Three missense mutations (I80N, T481M, P578S) were expressed in Cos7 cells to study the effects on arylsulfatase E catalytic activity. These mutations caused impaired enzymatic activity suggesting that they are responsible for the disease. Two nonsense mutations, W581X in four patients and R540X in one, were found. One patient showed an insertion (T616ins). In three patients we found deletions of the ARSE gene: in one the deletion involved only the 3' end of the gene, while in two the ARSE gene was completely deleted.

Brachytelephalangic dwarfism due to the loss of ARSE and SHOX genes resulting from an X;Y translocation

Here we report an 8-year-old male patient who had mesomelic shortening of forearms and legs, brachytelephalangia and ichthyotic skin lesions. Chromosomal analysis showed an X;Y translocation involving the short arm of the X chromosome (Xp). Fluorescence in situ hybridization (FISH) and molecular studies localized the breakpoints on Xp22.3 in the immediate vicinity of the KAL gene demonstrating deletions of steroid sulfatase (STS), arylsulfatase E (ARSE), and short stature homeo box (SHOX) genes. It was suspected that the patient was suffering from chondrodysplasia punctata because of a loss of the arylsulfatase E (ARSE) gene. However, no stippled epiphyses were to be seen in the neonatal radiograph. Interestingly, this patient is the first case with a proven loss of the ARSE gene without chondrodysplasia punctata, assuming that chondrodysplasia punctata is not an obligatory sign of ARSE gene loss. Brachytelephalangia was the only result of ARSE gene deletion in this case. The patient's mother also had dwarfism and showed Madelung deformity of the forearms. She was detected as a carrier of the same aberrant X chromosome. The male patient did not show Madelung deformity, demonstrating that Lerri-Weill syndrome phenotype may be still incomplete in children with SHOX gene deletion. The wide clinical spectrum in the male and the Leri-Weill phenotype in his mother are the results of both a deletion involving several sulfatase genes in Xp22.3 and the SHOX gene located in the pseudoautosomal region. Nevertheless, there is no explanation for the absence of chondrodysplasia punctata despite the total loss of the ARSE gene. Further studies are necessary to investigate genotype/phenotype correlation in cases with translocations or microdeletions on Xp22.3, including the ARSE and the SHOX gene loci.

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.

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.

Brachytelephalangic chondrodysplasia punctata with distinctive phenotype and normal karyotype

We present two sibs with a distinctive phenotype and with stippled calcifications of the tarsal bones and sacro-coccygeal spine. They represent an apparently "new" form of chondrodysplasia punctata.

X-linked recessive chondrodysplasia punctata due to a new point mutation of the ARSE gene

Chondrodysplasia punctata (CP) is a heterogeneous group of bone dysplasias that are characterized by abnormal calcium deposition in areas of enchondral bone formation. The existence of an X-linked recessive form of chondrodysplasia punctata (CDPX) has been recognized in patients who are nullisomic for the Xp22.3 region, presenting with complex phenotypes. The gene of CDPX has been identified recently, and five point mutations of the gene, named ARSE, have been described. Here, we report on the clinical and molecular characterization of a patient with CDPX. The patient presented at birth with cranial and facial anomalies and short stature; an x-ray skeletal survey showed punctate calcifications and striking hand and foot abnormalities. Single strand conformation polymorphism (SSCP) and sequence analysis of the patient's DNA allowed the identification of a new mutation of the ARSE gene; this mutation causes an amino acid substitution from cysteine to tyrosine at position 492 of the ARSE predicted protein product. The clinical description of patients with CDPX due to known mutation of the ARSE is of interest for the precise delineation of the clinical spectrum of the disease.

Ichthyotic and psoriasiform skin lesions along Blaschko's lines in a woman with X-linked dominant chondrodysplasia punctata

X-linked dominant chondrodysplasia punctata is a rare genodermatosis characterized by transient punctate epiphyseal calcifications and ichthyotic skin changes, usually resolving during early infancy. We describe the case of a 32-year-old woman with ichthyotic skin lesions that developed during early childhood and persisted into adulthood. Psoriasiform skin changes became evident for the first time during adulthood. Both the ichthyotic and psoriasiform skin lesions followed Blaschko's lines. This case is unique because of the coexistence of ichthyotic and psoriasiform skin changes in an adult with X-linked dominant chondrodysplasia punctata.

XXY male with X-linked dominant chondrodysplasia punctata (Happle syndrome)

Happle syndrome is an X-linked dominant disorder with presumed lethality in hemizygous males; familial occurrence is rare. We describe a family with Happle syndrome affecting individuals in 3 generations. A man in this family is the first known male patient with Happle syndrome. He is severely affected; this may be due to his 47,XXY karyotype.

A clinical and genetic study of X-linked recessive ichthyosis and contiguous gene defects

X-linked recessive ichthyosis (XLI) is caused by a deletion, or mutation, of the steroid sulphatase gene on the distal short arm of the X chromosome (Xp22.3). This region of the X chromosome is particularly susceptible to deletions. Such deletions can occasionally extend to involve neighbouring genes, causing a contiguous gene defect. Therefore, XLI may be associated with Kallmann's syndrome (KS), mental retardation, X-linked recessive chondrodysplasia punctata and short stature. We have reviewed 33 patients with XLI. Nine showed evidence of contiguous gene defects. A further four had neurological deficit sustained at the time of birth. This study highlights the importance of screening patients with X-linked recessive ichthyosis for neighbouring genetic disorders and, in particular, the early identification of KS, as delay in diagnosis may lead to infertility and osteoporosis. Parents should be warned about possible obstetric complications due to prolonged labour in future pregnancies.

Phenotype/karyotype correlations of Y chromosome aneuploidy with emphasis on structural aberrations in postnatally diagnosed cases

Over 600 cases with a Y aneuploidy (other than non-mosaic 47,XYY) were reviewed for phenotype/karyotype correlations. Except for 93 prenatally diagnosed cases of mosaicism 45,X/46,XY (79 cases), 45,X/47,XYY (8 cases), and 45,X/46,XY/47,XYY (6 cases), all other cases were ascertained postnatally. Special emphasis was placed on structural abnormalities. This review includes 11 cases of 46,XYp-; 90 cases of 46,XYq- (52 cases non-mosaic; 38 cases 45,X mosaic); 34 cases of 46,X,r(Y) (9 cases non-mosaic and 25 cases 45,X mosaic); 8 cases of 46,X,i(Yp) (4 non-mosaic and 4 mosaic with 45,X); 12 cases of 46,X,i(Yq) (7 non-mosaic and 5 mosaic); 44 cases of 46,X,idic(Yq); 80 cases of 46,X, idic(Yp) (74 cases had breakpoints at Yq11 and 6 cases had breakpoints at Yq12); 130 cases of Y/autosome translocations (50 cases with a Y/A reciprocal translocation, 20 cases of Y/A translocation in 45,X males, 60 cases of Y/DP or Y/Gp translocations); 52 cases of Y/X translocations [47 cases with der(X); 4 cases with der(Y), and 1 case with 45,X with a der(X)], 7 cases of Y/Y translocations; 151 postnatally diagnosed cases of 45,X/46,XY; 14 postnatally diagnosed cases of 45,X/47,XYY; 18 cases of 45,X/46,XY/47,XYY; and 93 aforementioned prenatally diagnosed cases with a 45,X cell line. It is clear that in the absence of a 45,X cell line, the presence of an entire Yp or a region of it including SRY would lead to a male phenotype in an individual with a Y aneuploidy, whereas the lack of Yp invariably leads to a female phenotype with typical or atypical Ullrich-Turner syndrome (UTS). Once there is a 45,X cell line, regardless of whether there is Yp, Yq, or both Yp and Yq, or even a free Y chromosome in other cell line, there is an increased chance for that individual to be a phenotypic female with UTS manifestations or to have ambiguous external genitalia. This review once again shows a major difference in reported phenotypes between postnatally and prenatally diagnosed cases of 45,X/46,XY, 45,X/47,XYY, and 45,X/46,XY/47,XYY mosaicism. It appears that ascertainment bias can explain the fact that all known patients with postnatal diagnosis are phenotypically abnormal, while over 90% of prenatally diagnosed cases are reported to have a normal male phenotype. Further elucidation of major Y genes and their clinical significance can be expected in the rapidly expanding gene mapping projects. More, consequently better, phenotype/karyotype correlations can be anticipated at both the cytogenetic and the molecular level.

A high resolution deletion map of human chromosome Xp22

We have developed a 32-interval deletion panel for human chromosome Xp22 spanning about 30 megabases of genomic DNA. DNA samples from 50 patients with chromosomal rearrangements involving Xp22 were tested with 60 markers using a polymerase chain reaction strategy. The ensuing deletion map allowed us to confirm and refine the order of previously isolated and newly developed markers. Our mapping panel will provide the framework for mapping new sequences, for orienting chromosome walks in the region and for projects aimed at isolating genes responsible for diseases mapping to Xp22.

Absent chondrodysplasia punctata in a male with an Xp terminal deletion involving the putative region for CDPX1 locus

This is a follow-up report on a male patient with a 46,Y,r(X) karyotype. Although he had no clinico-radiological features of X-linked recessive chondrodysplasia punctata (CDPX1), molecular studies revealed an Xp terminal deletion involving the putative region for the CDPX1 locus (PABX-DXS31). We suspect that the absence of CDPX1 may be attributable to the nature of the disease and the extreme short stature of the patient (mean -5.6 S.D.).

Chondrodysplasia punctata: another possible X-linked recessive case

A 22-week fetus who had died in utero had a markedly hypoplastic nose and other facial abnormalities, short fingers, hypoplastic nails, and small phallus. Radiologically there was symmetrical cartilaginous stippling of the vertebral column, femoral heads, calcanei and elbows typical of chondrodysplasia punctata (CP), and metacarpal shortness and tiny pyramidal phalanges. The several causally different forms of CP are tabulated. Differential diagnosis suggests that the present case, which does not have limb shortness, could be a case of X-linked recessive brachytelephalangic chondrodysplasia punctata.

Exclusion mapping of the X-linked dominant chondrodysplasia punctata/ichthyosis/cataract/short stature (Happle) syndrome: possible involvement of an unstable pre-mutation

Homology with the mouse bare patches mutant suggests that the gene for the X-linked dominant chondrodysplasia punctata/ichthyosis/cataract/short stature syndrome (Happle syndrome) is located in the human Xq28 region. To test this hypothesis, we performed a linkage study in three families comprising a total of 12 informative meioses. Multiple recombinations appear to exclude the Xq28 region as the site of the gene. Surprisingly, multiple crossovers were also found with 26 other markers spread along the rest of the X chromosome. Two-point linkage analysis and analysis of recombination chromosomes seem to exclude the gene from the entire X chromosome. Three different mechanisms are discussed that could explain the apparent exclusion of an X-linked gene from the X chromosome by linkage analysis: (a) different mutations on the X chromosome disturbing X inactivation, (b) metabolic interference, i.e. allele incompatibility of an X-linked gene, and (c) an unstable pre-mutation that can become silent in males. We favour the last explanation, as it would account for the unexpected sex ratio (M:F) of 1.2:1 among surviving siblings, and for the striking clinical variability of the phenotype, including stepwise increases in disease expression in successive generations.

Chondrodysplasia punctata: a boy with X-linked recessive chondrodysplasia punctata due to an inherited X-Y translocation with a current classification of these disorders

Chondrodysplasia punctata (CDP) is a heterogeneous group of rare bone dysplasias characterized by punctate calcification of cartilage. The punctate calcifications are non-specific and have been seen in a wide variety of disorders including the Zellweger syndrome, warfarin, dilantin, alcohol and rubella embryopathies, vitamin-K-epoxide-reductase deficiency, chromosome trisomies 18 and 21, the Smith-Lemli-Opitz syndrome, prenatal infectious chondritis, hypothyroidism, and other rare disorders. We report on a boy with short stature, developmental delay, nasal hypoplasia, telebrachydactyly, hypoplastic genitalia, CDP, ichthyosis, hypoplastic genitalia, and a 46-X,+der(X),t(X;Y)(p22.31;q11.21), Y karyotype. Genomic DNA probe analysis was interpreted as showing that the translocation breakpoint was within the X-linked Kallmann syndrome gene. We review a current classification of these disorders that includes 3 well-defined single gene disorders. These include an autosomal recessive rhizomelic type with early lethality, an X-linked dominant type with presumed male lethality, and an X-linked recessive type that has only been described as part of a contiguous gene deletion syndrome.

Gene mapping of ocular diseases

Increasing awareness of the role of genetic factors in the causation of many human eye diseases has made ocular genetics one of the fastest growing areas of ophthalmology. The objective of this paper is to present the basic principles of gene mapping and their application to ophthalmology. The techniques used to map the genome are reviewed with emphasis placed on molecular genetics. The advances in this area have already provided the major impetus to the areas of diagnosis and prevention of some genetic eye disorders. Tables are presented that list the autosomal, X-linked and mitochondrial assignment of eye genes and disorders with ocular involvement.

Deletion of the distal short arm of the X chromosome (Xp) in a patient with short stature, chondrodysplasia punctata, and X-linked ichthyosis due to steroid sulfatase deficiency

We observed a boy with short stature, chondrodysplasia punctata, ichthyosis, and a terminal deletion of Xp. Steroid sulfatase deficiency was demonstrated in the patient's fibroblasts. Molecular analysis showed a deletion of the entire steroid sulfatase gene. This case represents another example of a contiguous gene syndrome in which the co-deletion of adjacent genes on a chromosome is responsible for a complex phenotype.

Two cases of steroid sulfatase deficiency with complex phenotype due to contiguous gene deletions

We report contiguous gene deletions in the distal short arm of the X chromosome in two patients with ichthyosis, due to steroid sulfatase deficiency, and other complex phenotypes. One patient had chondrodysplasia punctata (CDP) and ichthyosis with a normal chromosome constitution. Another patient had a CDP-like phenotype, ichthyosis, and hypogonadism. His karyotype was 46, -X,Y, +der(X)t(X;Y)(p22;q11). DNA from the two patients was analyzed by Southern blotting using cloned fragments mapped in the Xp21-Xpter region to investigate gene deletions. DNA from the patient with CDP showed a gene deletion of the STS, DXS31, and DXS89 loci, and DNA from the patient with X-Y translocation lacked fragments of the STS, DXS31, DXS89, and DXS143 loci. These findings suggest that the common deleted region involving the STS locus might have caused the similar phenotypes in both patients.

Heterozygous expression of X-linked chondrodysplasia punctata. Complex chromosome aberration including deletion of MIC2 and STS

Two females showing partial expression of X-linked chondrodysplasia punctata were identified in a family. Bone dysplasia was caused by an aberrant X chromosome that had an inverse duplication of the segment Xp21.2-Xp22.2 and a deletion of Xp22.3-Xpter. To characterise the aberrant X chromosome, dosage blots were performed on genomic DNA from a carrier using a number of X-linked probes. Anonymous sequences from Xp21.2-Xp22.2 to which probes D2, 99.61, C7, pERT87-15, and 754 bind were duplicated on the aberrant X chromosome. The proposita was heterozygous for all these markers. Dosage blots also showed that the loci for steroid sulfatase and the cell surface antigen 12E7 (MIC2) were deleted as expected from the cytogenetic results. Mouse human cell hybrids were constructed that retained the normal X in the active state. Analysis of these hybrid clones for the markers from Xp21.2-Xp22.2 revealed that all the alleles of the informative markers, present in a single dosage in the genomic DNA, were carried on the normal X chromosome of the proposita. The duplicated X chromosome therefore had two identical alleles, indicating that the aberration resulted from an intrachromosomal rearrangement.

Localization of the X-linked ocular albinism gene (OA1) between DXS278/DXS237 and DXS143/DXS16 by linkage analysis

Linkage analysis was performed in six families segregating for X-linked ocular albinism of the Nettleship-Falls type using four polymorphic DNA markers from the distal Xp. Linkage was found between the disease locus (OA1) and the loci DXS237 (theta max = 0.06, Zmax = 2.82), DXS278 (theta max = 0.03, Zmax = 5.27) and DXS16 (theta max = 0.10, Zmax = 2.33). The analysis of multiple informative meioses suggests that OA1 maps between DXS278/DXS237 and DXS143/DXS16. Multipoint linkage analysis slightly favours the order DXS278/DXS237-OA1-DXS16. These data refine the genetic localization of OA1 and may be useful for carrier detection in X-linked ocular albinism by DNA analysis.

An interstitial deletion in Xp22.3 in a family with X-linked recessive chondrodysplasia punctata and short stature

In a four-generation family, chondrodysplasia punctata was found in a boy and one of his maternal uncles. These two patients also have short stature, as do all female members of the family, DNA molecular analysis of the pseudoautosomal and Xp22.3-specific loci revealed the presence of an interstitial deletion that cosegregates with the phenotypic abnormalities. The proximal breakpoint of this deletion was located distal to the DXS31 locus and the distal breakpoint in the pseudoautosomal region between DXYS59 and DXYS17. This maps the recessive X-linked form of chondrodysplasia punctata between the proximal boundary of the pseudoautosomal region and DXS31, and an Xp gene controlling growth between DXYS59 and DXS31.

Long-range restriction map of the terminal part of the short arm of the human X chromosome

The terminal part of the short arm of the human X chromosome has been mapped by pulsed-field gel electrophoresis (PFGE). The map, representing the distal two-thirds of Xp22.3 spans a total of 10,000 kilobases (kb) from Xpter to the DXS143 locus. A comparison with linkage data indicates that 1 centimorgan (cM) in this region corresponds to about 600 kb. CpG islands were essentially concentrated in the 1500 kb immediately proximal to the pseudoautosomal boundary. Several loci, including the gene encoding steroid sulfatase (STS) and the loci for the X-linked recessive form of chondrodysplasia punctata (CDPX) and for Kallmann syndrome (KAL) have been placed relative to the Xp telomere. CDPX is located between 2650 and 5550 kb from Xpter, and STS is located between 7250 and 7830 kb from Xpter. KAL maps to an interval of 350 kb between 8600 and 8950 kb from the telomere. The X-chromosomal breakpoints of a high proportion of XX males resulting from X-Y interchange cluster to a 920-kb region proximal and close to the pseudoautosomal boundary.

Two 46,XX,t(X;Y) females with linear skin defects and congenital microphthalmia: a new syndrome at Xp22.3

We describe two females with de novo X;Y translocations, who presented at birth with irregular linear areas of erythematous skin hypoplasia involving the head and neck, along with eye findings that included microphthalmia, corneal opacities, and orbital cysts. The features in these children are similar to but distinct from those seen in females with Goltz syndrome and incontinentia pigmenti. Cytogenetic analysis has shown the X chromosome breakpoint in both females to be at Xp22.3. We suggest that this syndrome is the result of a deletion or disruption of DNA sequences in the region of Xp22.3.

Contiguous gene syndromes due to deletions in the distal short arm of the human X chromosome

Mendelian inherited disorders due to deletions of adjacent genes on a chromosome have been described as "contiguous gene syndromes." Short stature, chondrodysplasia punctata, mental retardation, steroid sulfatase deficiency, and Kallmann syndrome have been found as isolated entities or associated in various combinations in 27 patients with interstitial and terminal deletions involving the distal short arm of the X chromosome. The use of cDNA and genomic probes from the Xp22-pter region allowed us to identify 12 different deletion intervals and to confirm, and further refine, the chromosomal assignment of X-linked recessive chondrodysplasia punctata and Kallmann syndrome genes. A putative pseudoautosomal gene affecting height and an X-linked non-specific mental retardation gene have been tentatively assigned to specific intervals. The deletion panel described is a useful tool for mapping new sequences and orienting chromosome walks in the region.

Male infant with ichthyosis, Kallmann syndrome, chondrodysplasia punctata, and an Xp chromosome deletion

We report on a male infant with X-linked ichthyosis, X-linked Kallmann syndrome, and X-linked recessive chondrodysplasia punctata (CPXR). Chromosome analysis showed a terminal deletion with a breakpoint at Xp22.31, inherited maternally. This patient confirms the localization of XLI, XLK, and CPXR to this region of the X chromosome and represents an example of a "contiguous gene syndrome." A comparison of the manifestations of patients with CPXR, warfarin embryopathy, and vitamin K epoxide reductase deficiency shows a remarkable similarity. However, vitamin K epoxide reductase deficiency does not appear to be the cause of CPXR. We propose that CPXR may be due to a defect in a vitamin K-dependent bone protein such as vitamin K-dependent bone carboxylase, osteocalcin, or matrix Gla protein.

Brachytelephalangic chondrodysplasia punctata: a possible X-linked recessive form

The author describes four cases of chondrodysplasia punctata with an hypoplasia of the distal phalanges of the fingers. In these cases, growth disturbance is moderate without asymmetry of the limbs, and the facial dysmorphism is similar to that found in Binder's maxillo-facial dysostosis. The phalangeal anomaly is very important for the diagnosis of chondrodysplasia punctata at an age when epiphyseal stippling is no longer present. The relationship of this form of chondrodysplasia with cases in which there is a deletion of the terminal short arm of the X chromosome is discussed. A possible hypothesis is that this form, which is always observed in males, is secondary to an isolated mutation of the Xp localized gene.

Molecular characterization of human X/Y translocations suggests their aetiology through aberrant exchange between homologous sequences on Xp and Yq

Several DNA sequences from two homologous regions, localized on the distal part of the human X chromosome short arm and on the long arm of the Y chromosome, have been hybridized to DNAs from seven human-rodent hybrids containing human X; Y translocation chromosomes. Molecular characterization of the translocated chromosomes has revealed, in all but one case, transfer of the Y cluster of sequences and complete deletion of the corresponding X-chromosomal sequences. The possible role of X/Y homology in the aetiology of X; Y translocations is proposed.

Molecular heterogeneity of steroid sulfatase deficiency: a multicenter study on 57 unrelated patients, at DNA and protein levels

Steroid sulfatase (STS) deficiency is the biochemical defect of X-linked ichthyosis (XLI), one of the most common X-linked disorders. We studied 57 European unrelated patients affected by STS deficiency. Twenty-eight patients were from Italy, 24 from the United Kingdom, 4 from The Netherlands, and 1 from Denmark. In two families XLI was associated with Kallmann syndrome (hypogonadotropic hypogonadism and anosmia). STS enzymatic activity was profoundly deficient in all cases. Direct DNA analysis, using cDNA and genomic probes from the STS gene and linked regions, demonstrated heterogeneity of the molecular defect. Forty-eight patients (84%) showed a deletion of the STS gene. In 44 cases the deletion also involved the STS flanking locus DXS237. In 1 patient a partial deletion of the STS gene was detected and in 9 patients no evidence of deletion was found. Locus DXS31 (probe M1A), previously mapped to Xp22.3-pter, was not deleted either in 24 patients with X-linked ichthyosis or in two families with X-linked ichthyosis associated with Kallmann syndrome. Consequently, the following loci order could be suggested: telomere--DXS31--(DXS237, STS)--Kallmann--centromere. Immunoblotting experiments, performed using anti-STS polyclonal antibodies, revealed the absence of cross-reacting material to STS in all cases tested, including 4 patients without evidence of deletions.