Two cases of X/autosome translocation in females with incontinentia pigmenti

Familial whole-arm translocations (1;19), (9;13), and (12;21): a review of 101 constitutional exchanges

We report here on 3 familial whole-arm translocations (WATs), namely the 8th instance of t(1;19)(p10;q10) and 2 novel exchanges: t(9;13)(p10;q10) and t(12;21)(p10;q10). The exchanges (1;19) and (12;21) were ascertained through a balanced carrier, whereas the t(9;13) was first diagnosed in a boy with a trisomy 9p syndrome and der(9p13p). Results of FISH analyses with the appropriate ?-satellite probes were as follows. Family 1, t(1;19): the D1Z5 probe gave a strong signal on both the normal chromosome 1 and the der(1q19p) as well as a weak signal on the der(1p19q). Family 2, t(9;13): the centromere-9 alphoid and D13Z1/D21Z1 probes under standard stringency gave no signal on the der(9p13p) in both the proband and a carrier brother, whereas the der(9q13q) was labelled only with the centromere-9 alphoid repeat in the latter; yet, this probe under low stringency revealed a residual amount of alphoid DNA on the der(9p13p) in the carrier. Family 3, t(12;21): the D12Z3 probe gave a signal on the normal chromosome 12 and the der(12p21q), whereas the D13Z1/D21Z1 repeat labelled the der(12q21p), the normal chromosome 21, and both chromosomes 13. Out of 101 WATs compiled here, 73 are distinct exchanges, including 32 instances between chromosomes with common alphoid repeats. Moreover, 7/9 of recurrent WATs involved chromosomes from the same alphoid family. Thus constitutional WATs appear to recur more frequently than other reciprocal exchanges, often involve chromosomes with common alphoid repeats, and can mostly be accounted for the great homology in alphoid DNA that favours mispairing and illegitimate nonhomologous recombination.

Abnormal pigmentation in hypomelanosis of Ito and pigmentary mosaicism: the role of pigmentary genes

There is increasing evidence that hypomelanosis of Ito and related disorders such as linear and whorled naevoid hypermelanosis are due to mosaicism for a variety of chromosomal abnormalities. This group of disorders is better termed 'pigmentary mosaicism'. In this review we explain how disparate chromosomal abnormalities might manifest as a common pigmentary phenotype. In particular, we provide evidence supporting the hypothesis that the chromosomal abnormalities reported in these disorders specifically disrupt expression or function of pigmentary genes.

Infantile Epileptic Encephalopathy with Hypsarrhythmia (Infantile Spasms/West Syndrome)

Infantile spasms is a unique disorder peculiar to infancy and early childhood. In this article, the clinical manifestations and electroencephalographic features of the disorder are described. The possible pathophysiologic mechanisms underlying infantile spasms and the relation of this disorder to other childhood encephalopathies are discussed. Finally, the treatment of patients with infantile spasms and their long-term outcome are briefly reviewed.

Incontinentia pigmenti: a review and update on the molecular basis of pathophysiology

Incontinentia pigmenti is an uncommon X-linked dominant disorder, lethal in the majority of affected males in utero and variably expressed in females. Cutaneous manifestations are classically subdivided into 4 stages: vesicular, verrucous, hyperpigmented, and atrophic. Various hair and nail abnormalities, dental anomalies, and ophthalmologic and neurologic deficits are associated with the disorder. The gene for incontinentia pigmenti has been mapped to Xq28. Recently, mutations in the NEMO/IKKgamma gene located at Xq28 have been found to cause expression of the disease. Knockout mice heterozygous for NEMO/IKKgamma gene deficiency develop a clinical phenotype very similar to that of incontinentia pigmenti. NEMO/IKKgamma is an essential component of the newly discovered nuclear factor kappaB (NF-kappaB) signaling pathway. When activated, NF-kappaB controls the expression of multiple genes, including cytokines and chemokines, and protects cells against apoptosis. The mechanism by which NEMO/IKKgamma deficiency causes, via the NF-kappaB pathway, the phenotypical expression of the disease has recently been elucidated. In addition, the newest research findings on eosinophil recruitment through eotaxin release by activated keratinocytes are described in the review. Finally, anhidrotic ectodermal dysplasia with immunodeficiency, a disorder allelic to incontinentia pigmenti, is discussed together with implications on the current understanding of NF-kappaB function. (J Am Acad Dermatol 2002;47:169-87.)

LEARNING OBJECTIVE

At the completion of this learning activity, participants will have a comprehensive and current understanding of incontinentia pigmenti, including its typical and uncommon clinical and histopathologic characteristics, diagnostic assessment, and current management strategies. Additionally, participants will gain the most current knowledge of the genetic and molecular basis of cutaneous pathomechanism.

A pregnancy following PGD for X-linked dominant [correction of X-linked autosomal dominant] incontinentia pigmenti (Bloch-Sulzberger syndrome): case report

Incontinentia Pigmenti (Bloch-Sulzberger syndrome) is a rare multisystem, ectodermal disorder associated with dermatological, dental and ocular features, and in <10% of cases, severe neurological deficit. Pedigree review suggests X-linked dominance with lethality in affected males. Presentation in female carriers is variable. Following genetic counselling, a mildly affected female carrier diagnosed in infancy with a de novo mutation was referred for preimplantation sexing, unusually selecting for male gender, with an acceptance of either normality or early miscarriage in an affected male. Following standard in-vitro fertilization and embryo biopsy, fluorescence in situ hybridization (FISH) unambiguously identified two male and two female embryos. A single 8-cell, grade 4 male embryo was replaced. A positive pregnancy test was reported 2 weeks after embryo transfer, although ultrasonography failed to demonstrate a viable pregnancy. Post abortive fetal tissue karyotyping diagnosed a male fetus with trisomy 16. This is an unusual report of preimplantation genetic diagnosis (PGD) being used for selection of males in an X-linked autosomal dominant disorder and demonstrates the value of PGD where amniocentesis or chorion villus sampling followed by abortion is not acceptable to the patient. This case also demonstrates the importance of follow-up prenatal diagnosis.

Hypomelanosis of Ito: clinical syndrome or just phenotype?

The term hypomelanosis of Ito is applied to individuals with skin hypopigmentation along the lines of Blaschko. Even though originally described as a purely cutaneous disease, subsequent reports have included a 33% to 94% association with multiple extracutaneous manifestations mostly of the central nervous and musculoskeletal systems leading to frequent characterization as a neurocutaneous disorder. A number of reports claimed familial occurrence and supported single gene inheritance for hypomelanosis of Ito, but none has been proved. Miscellaneous chromosomal mosaicisms have been demonstrated in some but not all affected individuals. Thus, it has been suggested that hypomelanosis of Ito is not a single condition but rather a nonspecific manifestation (ie, a phenotype) of chromosomal mosaicism and that this term should now be dropped. In this article, we review these developments focusing on the neurologic and genetic aspects of hypomelanosis of Ito. Our personal experience with 41 hypomelanosis of Ito patients and literature review led us to conclude that (1) the term hypomelanosis of Ito has been often misapplied to individuals with nonspecific "patchy depigmentation of the skin" who had several conditions of different etiologies; (2) the white matter involvement seen at neuroimaging in most of our hypomelanosis of Ito patients was similar to that reported in well-defined neurocutaneous disorders, including Sjögren-Larsson syndrome and incontinentia pigmenti; (3) whatever figures we take for associated central nervous system abnormalities in hypomelanosis of Ito, these represent the most frequent extracutaneous findings and, therefore, the use of the term neurocutaneous disorder for hypomelanosis of Ito might well be appropriate.

Hypomelanosis of ITO. A study of 76 infantile cases

We show the complications observed in a large series of children with hypomelanosis of Ito (HI) or incontinentia pigmenti achromians, studied in a neurology service over 30 years. Of the 76 patients, 35 were male (46%) and 41 female (54%) with ages ranging from newborn to 10 years at the time of the first visit. They were thoroughly studied from the clinical, genetic, psychological, neuroradiological, with computed tomography (CT) and/or magnetic resonance imaging (MRI), and electroencephalographic (EEG) points of view. Mental retardation was observed in 43 cases (57%) of whom eight (10%) showed autistic behavior; 16 (21%) were borderline and only 17 (22%) had a normal mental level (IQ > 85). Thirty-seven patients (49%) had seizures, consisting of infantile spasms in six cases (8%). Twelve cases showed macrocephaly and coarse facies, six had microcephaly, and 14 showed hypotonia with pes valgus and genu valgus. Three cases of cerebellar hypoplasia, another of intracranial arteriovenous malformation and another of distal spinal muscular atrophy were observed as well. Some other anomalies, such as syndactyly, clinodactyly, abnormalities of the skeleton, asymmetry of the facies, ears, body and/or extremities, gynecomastia and asymmetrical breasts, short stature, oral alterations, congenital cardiopathies and genital anomalies, were also occasionally found. Three children died, but necropsy was performed only in one. Anatomical and histological studies did not disclose specific findings.

Functional Xp disomy and de novo t(X;13)(q10;q10) in a girl with hypomelanosis of Ito

We report on a 16 month old girl with hypomelanosis of Ito and a balanced de novo (X;13)(q10;q10) translocation in which the der(Xp13q) had the X centromere (as assessed by FISH with the DXZ3 probe). A functional Xp disomy was shown in a small proportion of cultured lymphocytes by means of a BrdU terminal pulse. This observation supports the notion of a distinct form of hypomelanosis of Ito resulting from a functional Xp disomy.

X inactivation analysis in a female with hypomelanosis of Ito associated with a balanced X;17 translocation: evidence for functional disomy of Xp

X inactivation analysis was performed on normal and hypopigmented skin samples obtained from a female with hypomelanosis of Ito associated with a balanced whole arm X;17 translocation. Severe skewing of X inactivation resulting in inactivity of the intact X was found in blood and cultures of both types of skin, but analysis of DNA prepared directly from hypopigmented skin showed significant inactivation of the translocated X, inconsistent with the usual mechanism of phenotypic expression in X;autosome translocations. In addition, dual colour FISH analysis using centromere specific probes for chromosomes X and 17 showed that the breakpoints on both chromosomes lie within the alphoid arrays, making interruption of a locus on either chromosome unlikely. While partial variable monosomy of loci on chromosome 17p cannot be excluded as contributing to the phenotype in this patient, it is argued that the major likely factor is partial functional disomy of sequences on Xp in cell lineages that have failed to inactivate the intact X chromosome.

Hypomelanosis of Ito and X;autosome translocations: a unifying hypothesis

Hypomelanosis of Ito is a sporadic multisystem disorder known to be associated in many cases with chromosomal mosaicism. While no particular pattern is generally evident for the specific chromosomes involved in such patients, a subgroup of female patients exists in whom the common factor is the presence of a balanced, constitutional X;autosome translocation, with a cytogenetic breakpoint in the pericentromeric region of the X. It is argued here that the phenotype in these cases results not from the interruption of X linked genes but from the presence of mosaic functional disomy of X sequences above the breakpoint.

Retinal photoreceptor dystrophies LI. Edward Jackson Memorial Lecture

PURPOSE

To assess the state of knowledge of photoreceptor dystrophies.

METHODS

The current literature concerning photoreceptor dystrophies is reviewed, and their potential impact on concepts of pathogenesis of disease and clinical practice is assessed.

RESULTS

As a result of cooperative investigative work between researchers in various disciplines, major advances in the classification of retinal photoreceptor dystrophies have been made. Until recently, classification of retinal dystrophies was based on clinical observation alone, and it was evident that this method was imprecise and of limited value. Largely through the work of molecular biologists, it has been shown that diseases clinically indistinguishable from one another may be a result of mutations on a variety of genes; conversely, different mutations on a single gene may give rise to a variety of phenotypes. It is reassuring that it is possible to generate concepts as to potential pathogenetic mechanisms that exist in retinal dystrophies in light of this new knowledge. More important for the clinician is the potential impact on clinical practice. There is as yet no therapy by which the course of most of these disorders can be modified. However, there is a considerable body of work in which therapeutic intervention is being explored, and many researchers now see treatment as a justifiable objective of their work.

CONCLUSIONS

Knowledge of the causative mutation is of value to the clinician in that it provides a precise diagnosis and allows the distribution of the abnormal gene to be documented fully within a family. To take full advantage of the opportunities provided by current research, clinical practice will have to be modified, particularly if therapy can be justified.

Chromosomal mosaicism in two patients with epidermal verrucous nevus. Demonstration of chromosomal breakpoint

Linear epidermal nevi are hamartomas that originate in embryonic ectoderm. For epidermal nevi associated with involvement of other systems, such as the skeleton or central nervous system, the term epidermal nevus syndrome has been introduced. Chromosomal aberrations have been suggested but not proven as an underlying cause. We performed cytogenetic studies of skin cells from two unrelated men who had a verruciform epidermal nevus. Variegated translocation mosaicism with an identical breakpoint localized at the long arm of chromosome 1 was present in both patients. Normal skin and blood lymphocytes showed normal karyotypes.

Chromosome rearrangements and human gene mapping

The successful mapping of numerous mendelian disorders by chromosome rearrangements turned out to be a key method for positional location of disease genes. We present some personal observations and comments on the interest of cytogenetic studies in human gene mapping.

Retinal and other manifestations of incontinentia pigmenti (Bloch-Sulzberger syndrome)

BACKGROUND

One of the largest series of patients with incontinentia pigmenti who have undergone detailed ophthalmologic examination is reported here, including previously unrecognized findings with visually disabling consequences.

METHODS

Thirteen females with incontinentia pigmenti from eight unrelated families were evaluated. The diagnosis of incontinentia pigmenti had been established previously by a referring pediatrician or dermatologist in 12 patients and by the authors in one other patient on the basis of retinal findings and history of characteristic skin manifestations.

RESULTS

Abnormalities of the eye, central nervous system, skeleton, teeth, and hair develop in a majority of patients. The authors describe the evolution of retinal vascular abnormalities, and, for the first time, document foveal hypoplasia (in 4 of their 13 patients). The authors also provide the first report of a child with a normal brain shown on computed tomographic scan at 3 days old, which evolved to devastating cerebral ischemia, edema, and cortical blindness beginning at 6 days old.

CONCLUSIONS

Incontinentia pigmenti should be included in the differential diagnosis of patients with peripheral retinal vascular nonperfusion, preretinal neovascularization, infantile retinal detachment, or foveal hypoplasia, particularly if there is evidence of characteristic dermatologic or other systemic manifestations. In infants with incontinentia pigmenti, retinal vascular anomalies are best detected by examination under anesthesia using fluorescein angiography.

Incontinentia pigmenti achromians (hypomelanosis of ITO, MIM 146150): further evidence of localization at Xp11

We report on a girl with apparent hypomelanosis of Ito (ITO); cytogenetic studies disclosed the karyotype 46,X,t(X;10)(p11;q11)mat. We present further evidence that at least one of the genetic forms of ITO is located at Xp11; reviewing the clinical characteristics of patients with incontinentia pigmenti type 1 (IP1) and ITO with X-autosome translocations, we suggest that IP1 and ITO represent allelic forms or a contiguous gene syndrome. Thus, different genetic alterations in this region (Xp11) give rise to ITO or IP1 or borderline phenotypes. We also suggest that all patients with ITO, due to Xp11 mutation, have functional or genetic mosaicisms.

Interaction of incontinentia pigmenti and factor VIII mutations in a female with biased X inactivation, resulting in haemophilia

We report a female infant born to a mother with incontinentia pigmenti (IP) and a father with haemophilia A, who manifests both disorders. Analysis of peripheral blood DNA from the infant, her mother, and two female relatives with IP showed a highly skewed pattern of X inactivation. Random patterns were observed in the infant's two sisters, who do not have IP and have normal carrier activity of factor VIII. Preferential inactivation of the X chromosome bearing the IP mutation, probably by negative selection, appears to have unmasked the factor VIII mutation on the infant's other X chromosome. This illustrates an unusual mechanism for the manifestation of an X linked disease in a heterozygous female.

A radiation hybrid map of the proximal short arm of the human X chromosome spanning incontinentia pigmenti 1 (IP1) translocation breakpoints

Radiation hybrid mapping was used in combination with physical mapping techniques to order and estimate distances between 14 loci in the proximal region of the short arm of the human X chromosome. A panel of radiation hybrids containing human X-chromosomal fragments was generated from a Chinese hamster-human cell hybrid containing an X chromosome as its only human DNA. Sixty-seven radiation hybrids were screened by Southern hybridization with sets of probes that mapped to the region Xp11.4-Xcen to generate a radiation hybrid map of the area. A physical map of 14 loci was constructed based on the segregation of the loci in the hybrid clones. Using pulsed-field gel electrophoresis (PFGE) analyses and a somatic cell hybrid mapping panel containing naturally occurring X; autosome translocations, the order of the 14 loci was verified and the loci nearest to the X-chromosomal translocation breakpoints associated with the disease incontinentia pigmenti 1 (IP1) were identified. The radiation hybrid panel will be useful as a mapping resource for determining the location, order, and distances between other genes and polymorphic loci in this region as well as for generating additional region-specific DNA markers.

Isolation of DNA markers from a region between incontinentia pigmenti 1 (IP1) X-chromosomal translocation breakpoints by a comparative PCR analysis of a radiation hybrid subclone mapping panel

A strategy based on the use of human-specific interspersed repetitive sequence (IRS)-PCR amplification was used to isolate regional DNA markers in the vicinity of the incontinentia pigmenti 1 (IP1) locus. A radiation hybrid (RH) resulting from a fusion of an irradiated X-only somatic cell hybrid (C12D) and a thymidine kinase deficient (TK-) hamster cell line (a23) was identified as containing multiple X chromosome fragments, including DNA markers spanning IP1 X-chromosomal translocation breakpoints within region Xp11.21. From this RH, a panel of subclones was constructed and analyzed by IRS-PCR amplification to (a) identify subclones containing a reduced number of X chromosome fragments spanning the IP1 breakpoints and (b) construct a mapping panel to assist in identifying regional DNA markers in the vicinity of the IP1 locus. By using this strategy, we have isolated three different IRS-PCR amplification products that map to a region between IP1 X chromosome translocation breakpoints. A total of nine DNA sequences have now been mapped to this region; using these DNA markers for PFGE analyses, we obtained a probe order DXS14-DXS422-MTHFDL1-DXS705. These DNA markers provide a starting point for identifying overlapping genomic sequences spanning the IP1 translocation breakpoints; the availability of IP1 translocation breakpoints should assist the molecular analysis of this locus.

X inactivation as a mechanism of selection against lethal alleles: further investigation of incontinentia pigmenti and X linked lymphoproliferative disease

Thirty-one females with incontinentia pigmenti (IP), 42 controls, and 11 females from four families segregating for X linked lymphoproliferative disease (XLP) were studied for evidence of skewed X inactivation by analysis of methylation at sites in the HPRT, PGK, and M27 beta (DXS255) regions of the X chromosome. Extensive skewing of X inactivation was present in blood from 4/42 (9.5%) control females and 11/31 (35%) of those with IP. This frequency of skewed inactivation was seen in both familial and sporadic cases of IP. Analysis of inactivation in mother/daughter pairs, both affected and control subjects, showed no familial consistency of pattern, arguing against specific mutations being associated with particular patterns of inactivation. In the only informative family where both mother and daughter were affected by IP and showed skewed inactivation, the IP mutation was on the active X chromosome. This argues against cell selection during early embryogenesis being the explanation for the skewed inactivation observed. These data confirm that skewed inactivation of one X is observed in lymphocytes from a significant minority of normal females, and is seen with raised frequency in IP heterozygotes. It is not, however, a universally observed phenomenon, and the relationship of X inactivity to the IP mutation appears to be complex. In the case of XLP, though skewed X inactivation patterns are seen in most disease carriers, the frequency with which this phenomenon occurs in normal females renders it an unreliable diagnostic marker for XLP carriers.

Functional disomies of the X chromosome influence the cell selection and hence the X inactivation pattern in females with balanced X-autosome translocations: a review of 122 cases

We reviewed 122 cases of balanced X-autosome translocations in females, with respect to the X inactivation pattern, the position of the X break point and the resulting phenotype. In 77% of the patients the translocated X chromosome was early replicating in all cells analysed. The break points in these cases were distributed all along the X chromosome. Most of these patients were either phenotypically normal or had gonadal dysgenesis, some had single gene disorders, and less than 9% had multiple congenital anomalies and/or mental retardation. In the remaining 23% of the cases the translocated X chromosome was late replicating in a proportion of cells. In these cells only one of the translocation products was reported to replicate late, while the remaining portion of the X chromosome showed the same replication pattern as the homologous part of the active, structurally normal X chromosome. The analysis of DNA methylation in one of these cases confirmed noninactivation of the translocated segment. Consequently, these cells were functionally disomic for a part of the X chromosome. The presence of disomic cells was highly prevalent in translocations with break points at Xp22 and Xq28, even though spreading of X inactivation onto the adjacent autosomal segment was noted in most of these cases. This suggests that selection against cells with a late replicating translocated X is driven predominantly by a functional disomy X, and that the efficiency of this process depends primarily on the position of the X break point, and hence the size of the noninactivated region.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Linear skin defects and congenital microphthalmia: a new syndrome at Xp22.2

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Aicardi syndrome: early neuroradiological manifestations and results of DNA studies in one patient

A patient with Aicardi syndrome is presented. We report results of DNA analysis from the patient and her parents with probes mapped to Xp21.3-22.3 in an attempt to localize a deletion in this region. No signs of a microdeletion could be detected, using 5 different DNA markers. Further, it is suggested that a specific combination of cerebral abnormalities may be characteristic of the syndrome and that antenatal ultrasonographic diagnosis may be feasible.

Incontinentia pigmenti: XXY male with a family history

We report on the case of a male who from the start of life displayed vesicular lesions; on the trunk these were clustered and on the limbs they adopted a linear configuration. After biopsy of one such lesion, the histopathological study was compatible with a diagnosis of incontinentia pigmenti (IP). In the following months, hyperkeratotic lesions appeared which later became pigmented. The mother and other female members of the family also showed different degrees of alteration related to the same disease. The karyotype study showed the existence of 47,XXY (Klinefelter syndrome). The exceptional nature of this case is that although it is the third case reported in the literature of a male affected by incontinentia pigmenti with a previous family history, it is the only one combining this characteristic with the presence of a 47,XXY karyotype.

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.

De novo deletion of Xp22.2-pter in a female with linear skin lesions of the face and neck, microphthalmia, and anterior chamber eye anomalies

A female infant is described with an unusual combination of eye and skin findings. Raw linear skin lesions on the face and neck were present at birth, healing to leave pigmented streaks. In addition she had left sided microphthalmia and bilateral sclerocornea. Chromosome analysis showed a terminal deletion of the short arm of the X chromosome (Xp22.2--pter). Clinical findings were similar to three previously described children with translocations involving Xp22.3. The condition probably represents a new syndrome distinct from incontinentia pigmenti and Goltz syndrome.

Mapping X-linked ophthalmic diseases. IV. Provisional assignment of the locus for X-linked congenital cataracts and microcornea (the Nance-Horan syndrome) to Xp22.2-p22.3

The Nance-Horan syndrome (NHS) is an infrequent X-linked disorder typified by dense congenital central cataracts, microcornea, anteverted and simplex pinnae, brachymetacarpalia, and numerous dental anomalies. The regional location of the genetic mutation causing NHS is unknown. The authors applied the modern molecular techniques of analysis of restriction fragment length polymorphisms to five multigenerational kindreds in which NHS segregated. Provisional linkage is established to two DNA markers--DXS143 at Xp22.3-p22.2 and DXS43 at Xp22.2. Regional localization of NHS will provide potential antenatal diagnosis in families at risk for the disease and will enhance understanding of the multifaceted genetic defects.

Incontinentia pigmenti in a male infant with Klinefelter syndrome

Incontinentia pigmenti is a familial disorder affecting tissues derived from neuroectoderm. Statistical analysis of reported pedigrees is consistent with transmission of incontinentia pigmenti by an X-linked dominant gene with male hemizygote lethality. This report describes a male infant with the classic clinical features of this condition and a 47,XXY chromosomal constitution. These findings support the concept that incontinentia pigmenti is an X-linked dominant disorder. This case illustrates the importance of a full genetic investigation in all males with physical findings suggestive of an X-linked dominant disorder lethal in males.

The gene for incontinentia pigmenti is assigned to Xq28

A linkage study of eight families with incontinentia pigmenti (IP) has been performed, and linkage to site DXS52 has been established. We suggest that the IP locus lies in the Xq terminal region on the long arm of the X chromosome.

Incontinentia pigmenti and X-autosome translocations. Non-isotopic in situ hybridization with an X-centromere-specific probe (pSV2X5) reveals a possible X-centromeric breakpoint in one of five published cases

Incontinentia pigmenti (IP) is a rare X-linked disease with marked female-to-female transmission and a dominant pattern of inheritance. Reports of six unrelated females with IP and X-autosomal translocations, all with the X breakpoint at Xp11, and an additional report of a female with IP and a 45,X/46,X,r(X) karyotype suggests that this may be the locus for the IP gene. When four of these cases, including the r(X), were re-examined with a non-isotopic in situ hybridization technique and an X centromere-specific probe (pSV2X5), the Xp11 breakpoint was confirmed. However, results from a fifth reported case, t(X;17), showed that the X breakpoint was within the centromeric alphoid repetitive sequences recognized by the probe pSV2X5. As the clinical presentation of this patient was consistent with the IP phenotype and diagnosis, the centromeric position of the X-chromosome breakpoint raises several questions with respect to the homogeneity of the Xp11 locus for IP.

Linkage studies do not confirm the cytogenetic location of incontinentia pigmenti on Xp11

Linkage studies have been performed in 5 incontinentia pigmenti (IP) families totaling 29 potentially informative meioses. Ten probes of the Xp arm were used, six of them were precisely localized on the X chromosome, using hamster X human somatic cell hybrids containing a broken X chromosome derived from an incontinentia pigmenti patient carrying an X;9 translocation [46,XX,t(X;9)(p11.21;q34)]. The following order for probes is proposed: pter - (DXS7, DXS146, DXS255) - IP1 - (DXS14, DXS90) - DXS106 - qter. The negative lod scores obtained exclude the possibility that in the families studied, the gene for IP is located in Xp11 or in the major part of the Xp arm.

Genetic counselling in hypomelanosis of Ito: case report and review

A 27-year-old male with hypomelanosis of Ito (HI) is reported. One of his two children had a postaxial ray defect of one leg but neither had cutaneous features of HI. Somatic mosaicism for a gene defect lethal to ectodermal derivatives offers the best explanation for HI in males, with consequent negligible recurrence risk. The limb defect is considered coincidental. The excess of girls with HI could be due to a female cohort with incontinentia pigmenti (IP) which may be indistinguishable: counselling of females must therefore take account of possible X-linked inheritance.

The gene for incontinentia pigmenti: failure of linkage studies using DNA probes to confirm cytogenetic localization

Probes for restriction fragment length polymorphisms mapping between Xp21 and Xq22.3 have been used in a linkage study of incontinentia pigmenti (IP). Six independent sporadic cases of disorders resembling IP with X-autosome translocations involving the same X chromosome breakpoint (Xp11) have been reported. These observations suggest that the IP gene may be located in the Xp11 chromosomal region. However, the linkage study with DNA probes has failed to confirm this localisation.

Microdeletion syndromes, balanced translocations, and gene mapping

High resolution prometaphase chromosome banding has allowed the detection of discrete chromosome aberrations which escaped earlier metaphase examinations. Consistent tiny deletions have been detected in some well established malformation syndromes: an interstitial deletion in 15q11/12 in the majority of patients with the Prader-Willi syndrome and in a minority of patients with the Angelman (happy puppet) syndrome; a terminal deletion of 17p13.3 in most patients examined with the Miller-Dieker syndrome; an interstitial deletion of 8q23.3/24.1 in a large majority of patients with the Giedion-Langer syndrome; an interstitial deletion of 11p13 in virtually all patients with the WAGR (Wilms' tumour-aniridia-gonadoblastoma-retardation) syndrome; and an interstitial deletion in 22q11 in about one third of patients with the DiGeorge sequence. In addition, a combination of chromosome prometaphase banding and DNA marker studies has allowed the localisation of the genes for retinoblastoma and for Wilms' tumour and the clarification of both the autosomal recessive nature of the mutation and the possible somatic mutations by which the normal allele can be lost in retina and kidney cells. After a number of X linked genes had been mapped, discrete deletions in the X chromosome were detected by prometaphase banding with specific attention paid to the sites of the gene(s) in males who had from one to up to four different X linked disorders plus mental retardation. Furthermore, the detection of balanced translocations in probands with disorders caused by autosomal dominant or X linked genes has allowed a better insight into the localisation of these genes. In some females with X linked disorders, balanced X; autosomal translocations have allowed the localisation of X linked genes at the breakpoint on the X chromosome. Balanced autosome; autosome translocations segregating with autosomal dominant conditions have provided some clues to the gene location of these conditions. In two conditions, Greig cephalopolysyndactyly and dominant aniridia, two translocation families with one common breakpoint have allowed quite a confident location of the genes at the common breakpoint at 7p13 and 11p13, respectively.

Research on Rett syndrome: strategy and preliminary results

The research strategy presented here involves four assumptions: (1) Rett syndrome exists; (2) a single cause will eventually be found to account for the majority of cases presently assigned to this disease category; (3) it is genetically determined; and (4) it represents a neurodegenerative disorder that can be defined by quantitative studies of nervous system structure and function. The strategy proposed here involves the comprehensive study of 100 patients with the classic Rett syndrome phenotype. Studies include the (1) search for a diagnostic marker; (2) high-resolution cytogenetic banding techniques, (3) quantitative morphologic studies of postmortem brain tissue as well as neurochemical analyses including autoradiographic techniques, radioimmunoassays, and in situ hybridization; and (4) positron emission tomography studies of cerebral glucose metabolism and neurotransmitters.

X-linked genetic homologies between mouse and man

X-linked genes are conserved among all mammalian species, but the organization of genes on the X chromosome varies from one species to another. This review summarizes the evidence for established gene homologies between mice and human beings. It also describes genes that are possible homologies because of their locations in the human and murine X chromosomes and similarities in the phenotypes they produce. Based on current knowledge of homologous gene location, the human and murine X chromosomes appear to contain four highly conserved segments and differ in organization by only three to four simple chromosomal rearrangements.

Gene for incontinentia pigmenti maps to band Xp11 with an (X;10) (p11;q22) translocation

Incontinentia pigmenti (IP) is a genetic disease that is usually lethal in males. We report finding an X;10 translocation in a girl with IP. Three other X/autosome translocations have been observed in females with IP: two involving chromosome 9 and one involving chromosome 17. The breakpoint in all four cases in the X chromosome was in band Xp11. The IP gene locus can therefore be confidently assigned to the X chromosome and, specifically, to band Xp11. The IP gene is most likely to subband Xp11.2. We propose that IP may prove to be a submicroscopic deletion.

Incontinentia pigmenti in a boy with Klinefelter's syndrome

A boy with the cutaneous lesions of incontinentia pigmenti is described. Chromosomal analysis revealed the 47,XXY karyotype of Klinefelter's syndrome. Since incontinentia pigmenti trait is usually lethal in males, the possibility of the second X chromosome protecting against fetal death is discussed.

Genes for synapsin I, a neuronal phosphoprotein, map to conserved regions of human and murine X chromosomes

Synapsin I is a neuron-specific phosphoprotein associated with the membranes of small synaptic vesicles. Its function is not entirely clear, but evidence points to a possible role in the regulation of neurotransmitter release. Its biosynthesis is under developmental control. Assignment of the human synapsin I gene to the X chromosome at band Xp11 was accomplished by in situ hybridization, using a rat cDNA probe. Southern blot analysis of DNAs from a panel of human-Chinese hamster somatic cell hybrids with defined regions of the human X chromosome confirmed the in situ mapping data. The mouse synapsin I gene was assigned to the X chromosome, proximal to band XD, by Southern blot analysis of Chinese hamster-mouse somatic cell hybrids with normal or rearranged mouse X chromosomes. In situ chromosomal hybridization experiments localized the mouse synapsin I gene more precisely to bands XA1----A4. These results add to the comparative gene map of mammalian species and support certain hypotheses regarding the evolutionary relationship between human and mouse X chromosomes. We hypothesize that the synapsin I gene could be mutated in human X-linked disorders with primary neuronal degeneration, such as the Rett syndrome.