A somatic cell hybrid panel to facilitate identification of DNA sequences in the vicinity of the incontinentia pigmenti locus (IP1)

Isolation and characterization of the faciogenital dysplasia (Aarskog-Scott syndrome) gene: a putative Rho/Rac guanine nucleotide exchange factor

Faciogenital dysplasia (FGDY), also known as Aarskog-Scott syndrome, is an X-linked developmental disorder characterized by disproportionately short stature and by facial, skeletal, and urogenital anomalies. Molecular genetic analyses mapped FGDY to chromosome Xp11.21. To clone this gene, YAC clones spanning an FGDY-specific translocation breakpoint were isolated. An isolated cDNA, FGD1, is disrupted by the breakpoint, and FGD1 mutations cosegregate with the disease. FGD1 codes for a 961 amino acid protein that has strong homology to Rho/Rac guanine nucleotide exchange factors (GEFs), contains a cysteine-rich zinc finger-like region, and, like the RasGEF mSos, contains two potential SH3-binding sites. These results provide compelling evidence that FGD1 is responsible for FGDY and suggest that FGD1 is a Rho/RacGEF involved in mammalian development.

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.

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.

Refined localization of human connexin32 gene locus, GJB1, to Xq13.1

Connexins are the peptide subunits of gap junctions that interconnect cells to allow the direct, intercellular transfer of small molecules. Recently, the human connexin32 gene (locus designation GJB1) has been regionally mapped by three other laboratories to Xp11-q13, Xcen-q22, and Xp11-q22. The smallest region of overlap from these studies is Xcen-q13. By using a series of somatic cell hybrid mapping panels and a rat connexin32 cDNA probe, we have localized the human GJB1 locus to a much smaller region in proximal Xq13.1, in interval 8, as described by Lafrenière et al. (8).

Father-to-daughter transmission of focal dermal hypoplasia associated with nonrandom X-inactivation: support for X-linked inheritance and paternal X chromosome mosaicism

Focal dermal hypoplasia (FDH) is a rare syndrome of severe developmental anomalies of the tissues and organs derived from ectoderm and mesoderm. Though data have suggested that FDH is an X-linked dominant trait associated with male hemizygote lethality, a hypothesis supported by the observation of three unrelated infants with FDH manifestations and de novo chromosome rearrangements involving Xp22, observations of father-to-daughter transmission have suggested possible genetic heterogeneity and autosomal dominant inheritance with sex limitation. We hypothesize that, if FDH is an X-linked disorder, cells expressing an active disease locus might experience a selective disadvantage resulting in a nonrandom pattern of X-inactivation in patient tissue. To test this hypothesis, we studied one of the two previously described families demonstrating father-to-daughter inheritance of FDH. To determine if the affected daughter had a skewed pattern of X-inactivation consistent with X-linked inheritance of FDH, somatic cell hybrids were constructed by fusing hypoxanthine phosphoribosyl transferase (HPRT)-deficient rodent fibroblasts with either patient dermal fibroblasts or peripheral white blood cells (WBCs); hybrid clones retaining an active X chromosome were analyzed to determine the parental origin of the active X chromosome. Analyses of resulting hybrid clones showed that while hybrids constructed from skin fibroblasts contained an active X chromosome inherited from either of the patient's parents, hybrids constructed from WBCs showed a skewed pattern of X-inactivation; 11 of 11 hybrids contained an active maternal X chromosome (chi 2 = 12.2, P = .001).(ABSTRACT TRUNCATED AT 250 WORDS)