R. A. Pfeiffer

A familial mutation in the testis-determining gene SRY shared by both sexes

A familial mutation in SRY, the gene coding for the testis-determining factor TDF, was identified in an XY female with gonadal dysgenesis, her father, her two brothers and her uncle. The mutation consists of a T to C transition in the region of the SRY gene coding for a protein motif known as the high mobility group (HMG) box, a protein domain known to confer DNA-binding specificity on the SRY protein. This point mutation results in the substitution, at amino acid position 109, of a serine residue for phenylalanine, a conserved aromatic residue in almost all HMG box motifs known. This F109S mutation was not found in 176 male controls. When recombinant wildtype SRY and SRYF109S mutant protein were tested in vitro for binding to the target site AAC AAAG, no differences in DNA-binding activity were observed. These results imply that the F109S mutation either is a rare neutral sequence variant, or produces an SRY protein with slightly altered in vivo activity, the resulting sex phenotype depending on the genetic back-ground or environmental factors.

A Novel 22q11.2 Microdeletion in DiGeorge Syndrome

We thank the family for their cooperation and patience, and we thank Silke Appel (Berlin) for help with the BAC screening.

Translocation breakpoints in three patients with campomelic dysplasia and autosomal sex reversal map more than 130 kb from SOX9

Campomelic dysplasia (CMPD1) and autosomal XY sex reversal (SRA1) are caused by mutations in the SRY-related gene SOX9 on 17q. Unexpectedly, the 17q breakpoints in four CMPD l translocation cases previously analyzed by us and others map 50 kb or more from SOX9. Here, we present clinical, cytogenetic, and molecular data from a new CMPD1/SRA1 patient with t(6; 17) (q14; q24). Fluorescence in situ hybridization has shown that the 17q breakpoint in this case maps to the same region as the breakpoints in the other translocation cases, at least 130 kb from SOX9. Likewise, the breakpoints in two of the previously described cases also map more than 130 kb and, as shown by pulsed field gel electrophoresis analysis, at most 400 kb or 690 kb from SOX9. By using a SOX9 coding sequence polymorphism, expression of both SOX9 alleles has been demonstrated by the reverse transcriptase polymerase chain reaction in lymphoblastoid cells from one of the translocation cases.

A study of ten small supernumerary (marker) chromosomes identified by fluorescence in situ hybridization (FISH)

In seven cases additional minute chromosomes studied by FISH were identified as no. 3, 11, 15, 18, 21 and X. Findings were unexpected except for partial trisomy 21 in an adolescent with minor features of Downs syndrome. Moreover, an i(18p) in a mentally retarded dysmorphic child and an idic(15) in a child with Fallot tetralogy was confirmed. In a child with r(21), a supernumerary marker was shown to be derived from no. 21, while in the mother an additional marker idic(22) was noted.

Identification of microdeletions spanning the Diamond-Blackfan anemia locus on 19q13 and evidence for genetic heterogeneity.

Summary Diamond-Blackfan anemia (DBA) is a rare pure red-cell hypoplasia of unknown etiology and pathogenesis. A major DBA locus has previously been localized to chromosome 19q13.2. Samples from additional families have been collected to identify key recombinations, microdeletions, and the possibility of heterogeneity for the disorder. In total, 29 multiplex DBA families and 50 families that comprise sporadic DBA cases have been analyzed with polymorphic 19q13 markers, including a newly identified short-tandem repeat in the critical gene region. The results from DNA analysis of 29 multiplex families revealed that 26 of these were consistent with a DBA gene on 19q localized to within a 4.1-cM interval restricted by loci D19S200 and D19S178; however, in three multiplex families, the DBA candidate region on 19q13 was excluded from the segregation of marker alleles. Our results suggest genetic heterogeneity for DBA, and we show that a gene region on chromosome 19q segregates with the disease in the majority of familial cases. Among the 50 families comprising sporadic DBA cases, we identified two novel and overlapping microdeletions on chromosome 19q13. In combination, the three known microdeletions associated with DBA restrict the critical gene region to ∼1 Mb. The results indicate that a proportion of sporadic DBA cases are caused by deletions in the 19q13 region.

An interstitial duplication of the X chromosome in a male allows physical fine mapping of probes from the Xq13-q22 region.

SummaryAn insertional translocation into the proximal long arm of the X chromosome in a boy showing muscular hypotony, growth retardation, psychomotor retardation, cryptorchidism, and Pelizaeus-Merzbacher disease (PMD) was identified as a duplication of the Xq21–q22 segment by employing DNA probes. With densitometric scanning for quantitation of hybridization signals, 15 Xq probes were assigned to the duplicated region. Analysis of the duplication allowed us to dissect the X-Y homologous region physically at Xq21 and to refine the assignments of the loci for DXYS5, DXYS12, DXYS13, DXS94, DXS95, DXS96, DXS111, and DXS211. Furthermore, we demonstrated the presence of two different DXYS13, and DXS17 alleles in genomic DNA of our patient, suggesting that the duplication resulted from a meiotic recombination event involving the two maternal X chromosomes.

Juvenile open angle glaucoma: fine mapping of the TIGR gene to 1q24.3-q25.2 and mutation analysis.

Abstract Autosomal dominant juvenile open angle glaucoma (JOAG) is an early-onset form of primary open angle glaucoma (POAG), which has been linked to chromosome 1q21–q31. Recently, mutations in the trabecular meshwork inducible glucocorticoid response gene (TIGR), one of the candidate genes mapped in this region, were identified in glaucoma patients of several families. We screened for mutations of the TIGR gene in two German families with JOAG and in 100 unselected sporadic cases of POAG. In the first family we identified a Pro370Leu mutation and in the second family a Gly367Arg mutation cosegregating with the glaucoma phenotype. No pathogenic mutation was found in 100 sporadic cases but a Tyr347Tyr polymorphism was found in two patients. Furthermore, fluorescence in situ hybridization (FISH) analysis was used to map a TIGR-specific yeast artificial chromosome to 1q24.3–q25.2.

Deficiency of coagulation factors VII and X associated with deletion of a chromosome 13 (q34). Evidence from two cases with 46,XY,t(13;Y)(q11;q34)

SummaryDeficiency of coagulation factors VII and X was found in two patients (Erlangen and Nancy) who shared the same chromosomal aberration 46,XY,t(13;Y)(q11;q34) with probable loss of a terminal segment of 13q. Loci involved in synthesis or constitution of these factors may be located at 13 (q34).

Incidence and significance of 22q11.2 hemizygosity in patients with interrupted aortic arch.

Interruption of the aortic arch (IAA) is a severe malformation of the heart with known association to DiGeorge syndrome (DGS) and 22q11.2 hemizygosity. The aim of this study was to establish incidence and significance of 22q11.2 hemizygosity in an unbiased sample of patients with IAA. All 15 children with IAA who were referred to our hospital in a 3-year period were tested by chromosome and fluorescence in situ hybridization (FISH) analysis with the probes D22S75, Tuplel, and cHKAD26 and by a set of 10 simple tandem repeat polymorphic (STRP) markers. In nine of 11 children with IAA type B, 22q11.2 hemizygosity was demonstrated by FISH and STRP analysis, but in none of the four children with type A. In all but one child, deletion size was approximately 3 Mb. The girl with the smaller deletion of approximately 1.5 Mb differed because of an Ullrich-Turner syndrome-like phenotype and severe T-cell defect. Additionally, in one patient with phenotypic signs of DGS, a small deletion distal to the known DGS region containing the marker D22S308 was suspected by STRP analysis. One deletion was shown to be inherited from a healthy father and one IAA type A recurred in a sib. T-cell anomalies were evident in eight of the nine children with classical deletion, five of whom suffered also from hypoparathyroidism. With respect to cause and clinical course, IAA type A and B were shown to represent different entities. This study showed that variable symptoms of 22q11.2 hemizygosity may cluster.

Langer‐Giedion syndrome and additional congenital malformations with interstitial deletion of the long arm of chromosome 8 46, XY, del 8 (q 13–22)

Deletion of the long arm of chromosome 8 was found in a mentally retarded boy with typical features of the Langer‐Giedion syndrome (TRP syndrome type II). Additional malformations were colobomata of the iris and partial syndactyly of the 4th and 5th fingers.