Karyotypes found in the population declared at increased risk of Down syndrome following maternal serum screening

Of the 65 328 pregnancies of South Australian mothers screened by the South Australian Maternal Serum Antenatal Screening (SAMSAS) Programme between 1 January 1991 and 31 December 1997, 3431 (5.25%) were declared at increased risk of fetal Down syndrome. Fetal or neonatal karyotype was determined in 2737/3431 (79.8%) of these pregnancies, including 16 with early fetal loss. Interrogation of the database of the South Australian Neonatal Screening Service showed 643 live-born infants whose phenotype was not subsequently questioned among the 694 pregnancies whose karyotype was not determined. Of the remaining 51/3431 pregnancies, 19 ended in early fetal loss without karyotyping and no newborn screening or other records could be found for 32 cases. The 129 instances of abnormal karyotype found were Down syndrome (84), trisomy 18 (four), trisomy 13 (three), triploidy (two), female sex chromosome aneuploidy (six) and male sex chromosome aneuploidy (five), inherited balanced rearrangements (19), mosaic or de novo balanced abnormalities (four) and unbalanced karyotypes (two). In the pregnancies declared at increased risk of fetal Down syndrome, only the karyotype for Down syndrome occurred with a frequency greater than that expected for the general, pregnant population.

Giant axonal neuropathy locus refinement to a < 590 kb critical interval

Giant axonal neuropathy (GAN) is a rare autosomal recessive neurodegenerative disorder, characterised clinically by the development of chronic distal polyneuropathy during childhood, mental retardation, kinky or curly hair, skeletal abnormalities and, ultrastructurally, by axons in the central and peripheral nervous systems distended by masses of tightly woven neurofilaments. We recently localised the GAN locus in 16q24.1 to a 5-cM interval between the D16S507 and D16S511 markers by homozygosity mapping in three consanguineous Tunisian families. We have now established a contig-based physical map of the region comprising YACs and BACs where we have placed four genes, ten ESTs, three STSs and two additional microsatellite markers, and where we have identified six new SSCP polymorphisms and six new microsatellite markers. Using these markers, we have refined the position of our previous flanking recombinants. We also identified a shared haplotype between two Tunisian families and a small region of homozygosity in a Turkish family with distant consanguinity, both suggesting the occurrence of historic recombinations and supporting the conclusions based on the phase-known recombinations. Taken together, these results allow us to establish a transcription map of the region, and to narrow down the GAN position to a < 590 kb critical interval, an important step toward the identification of the defective gene.

Characterization of regions of chromosomes 12 and 16 involved in nephroblastoma tumorigenesis

There are at least three loci involved in Wilms' tumor (WT) tumorigenesis: WT1 in 11p13, WT2 in 11p15.5, and WT3, as yet unmapped. A compilation of cytogenetic data published for 107 WT revealed that deletion of chromosome 16 and duplication of chromosome 12 occur as frequently as the well-documented 11p deletions. Allelic imbalance for chromosomes 16 and 12 was investigated in a series of 28 WT. By use of a large panel of restriction fragment length polymorphisms and (CA)n probes, we demonstrated loss of heterozygosity (LOH) for 16q in seven (25%) of the tumors. The whole length of 16q was involved in six of the tumors. Moreover, consistent with a previous report of 16q13 LOH in a sporadic WT and a constitutional breakpoint with a Beckwith-Wiedemann patient, we map a region of particular interest to between D16S308 and D16S320. The assumption that 16q LOH may be an early event was based on: 1) the detection of 16q LOH in one case of nephroblastomatosis; 2) the presence of a complete (clonal) 16q LOH in a tumor with partial (mosaic) 11p LOH; and 3) 16q LOH as the sole abnormality in one WT. By quantification of chromosome 12 allelic imbalance, we detected duplication in 18% of the total series and in 25% of the sporadic unilateral cases. The common region extended from the centromere to D12S7 in 12q21.1-q23. We also suggest that the various pathogenetically important loci are not equally involved in the different forms of WT and that their sequential involvement may differ.

Genetic heterogeneity in neuronal ceroid lipofuscinosis (NCL): evidence that the late-infantile subtype (Jansky-Bielschowsky disease; CLN2) is not an allelic form of the juvenile or infantile subtypes

The neuronal ceroid lipofuscinoses (NCLs) are a group of inherited neurodegenerative disorders characterized by the accumulation of autofluorescent lipopigment in neurons and other cell types. Inheritance is autosomal recessive. Three main childhood subtypes are recognized: infantile (Haltia-Santavuori disease; MIM 256743), late infantile (Jansky-Bielschowsky disease; MIM 204500), and juvenile (Spielmeyer-Sjögren-Vogt, or Batten, disease; MIM 204200). The gene loci for the juvenile (CLN3) and infantile (CLN1) types have been mapped to human chromosomes 16p and 1p, respectively, by linkage analysis. Linkage analysis of 25 families segregating for late-infantile NCL has excluded these regions as the site of this disease locus (CLN2). The three childhood subtypes of NCL therefore arise from mutations at distinct loci.

Regional mapping of human DNA excision repair gene ERCC4 to chromosome 16p13.13-p13.2

Mitomycin C (MMC)-resistant interspecific somatic cell hybrids made between human cells and the MMC-sensitive, Chinese hamster ovary (CHO) excision repair-deficient UV41 cells generally contained human chromosome 16, while other human chromosomes were randomly present. MMC-sensitive and -resistant subclones were isolated from resistant clones, and resistance generally segregated concordantly with human chromosome 16 markers. UV radiation survival analysis of subclones indicated that MMC and UV resistance were correlated. Therefore, the complementing gene, Excision Repair Cross Complementing 4 (ERCC4), was assigned to human chromosome 16. Complementation of UV41 by human cells derived from patients with xeroderma pigmentosum groups A, C, D and F excluded ERCC4 from involvement in those disease syndromes. Resistant hybrids containing only portions of chromosome 16 were identified by the lack of concordance of multiple chromosome 16 markers. When such hybrids were used as a source of probe for fluorescent in situ hybridization onto normal human metaphases, the only region of chromosome 16 identified as being consistently present was 16p13.1-p13.3. Genetic marker analysis of informative hybrids with mapped probes refined the position of ERCC4 to 16p13.13-p13.2 and allowed the following order of markers within the region to be established: pter--(PRM1, D16S215)-D16S213-D16S53-(D16S214,ERCC4) -D16S3-D16S96-cen.

Evaluation of a cosmid contig physical map of human chromosome 16

A cosmid contig physical map of human chromosome 16 has been developed by repetitive sequence finger-printing of approximately 4000 cosmid clones obtained from a chromosome 16-specific cosmid library. The arrangement of clones in contigs is determined by (1) estimating cosmid length and determining the likelihoods for all possible pairwise clone overlaps, using the fingerprint data, and (2) using an optimization technique to fit contig maps to these estimates. Two important questions concerning this contig map are how much of chromosome 16 is covered and how accurate are the assembled contigs. Both questions can be addressed by hybridization of single-copy sequence probes to gridded arrays of the cosmids. All of the fingerprinted clones have been arrayed on nylon membranes so that any region of interest can be identified by hybridization. The hybridization experiments indicate that approximately 84% of the euchromatic arms of chromosome 16 are covered by contigs and singleton cosmids. Both grid hybridization (26 contigs) and pulsed-field gel electrophoresis experiments (11 contigs) confirmed the assembled contigs, indicating that false positive overlaps occur infrequently in the present map. Furthermore, regional localization of 93 contigs and singleton cosmids to a somatic cell hybrid mapping panel indicates that there is no bias in the coverage of the euchromatic arms.

Molecular analysis of human chromosome 16 cosmid clones containing NotI sites

To test the feasibility of using cloned NotI sites as markers for physical mapping, we have screened for cosmid clones spanning the NotI sites on human Chromosome (Chr) 16. Fluorescence in situ hybridization analysis of these clones confirms the previously reported cluster of NotI sites on 16p13.3. Methylation status of the cloned NotI sites on genomic DNA was established by hybridization of the cosmids to Southern blots containing EcoRI and EcoRI/NotI digest of genomic DNA. These results indicated that four of six clones included in our study can be used as linking clones for physical mapping. Two clones have NotI sites which are not cleavable in the cell lines tested. In one clone, the NotI site exists as an isolated rare-cutting restriction enzyme site, whereas in the other clone the NotI site appears to be island-related.

Mapping of a cerebellar degeneration related protein and DXS304 around the fragile site

We have localized the gene encoding a cerebellar degeneration related (CDR) protein to a region proximal to the fragile site close to DXS98 and DXS105. This gene is polymorphic with the enzyme RsaI and therefore also provides a new genetic marker in this region. We have refined the localization of the locus DXS304 distal to the breakpoint in a patient suffering from Hunter disease. This confirms the localization of DXS304 distal to the fragile site previously suggested by linkage studies and localizes the fragile X mutation to a relatively small region between the Hunter breakpoint and the breakpoint in another hybrid B17.

Association of Treacher Collins syndrome and translocation 6p21.31/16p13.11: exclusion of the locus from these candidate regions

Treacher Collins syndrome (TCS) is an autosomal dominant defect of craniofacial development which has not been chromosomally localized. We have identified a mother and two children who have TCS and also a balanced translocation t(6;16)(p21.31;p13.11), which suggested the possibility that the TCS locus might be located at one of the translocation breakpoints. These were defined by in-situ hybridization as 6p21.31 (by using loci in the HLA complex defined by the probes p45.1DP beta 003/HLA-DPB2 and pRS5.10/HLA class I chain) and 16p13.11 (by using probes pACHF1.3.2/D16S8 and VK45/D16S131). Pairwise and multipoint linkage analysis using localized chromosome 6 probes and chromosome 16 probes in 12 unrelated TCS families with multiple affected siblings excluded the TCS locus from proximity to both translocation breakpoints. These data were confirmed when a third affected child, who did not exhibit the translocation, was born to the mother.

Quantification of progressive diabetic macular nonperfusion

We used the IS-2000 Image Analyzer to estimate the extent of progressive diabetic macular nonperfusion in a patient by means of an automatic clustering algorithm applied to digitized fluorescein angiograms of the patient's macula taken over time. This method may provide an objective and reproducible quantification of progressive macular nonperfusion.

A human retinoblastoma cell line expressing the common acute lymphoblastic leukemia antigen and displaying an unusual chromosome abnormality

A new continuous cell line derived from an untreated human retinoblastoma has been established. This cell line, FMC-RB1 is strongly positive for common acute lymphoblastic leukemia antigen and shows a number of ring chromosomes and two marker chromosomes considered to be derivations of chromosome #17; the nonrandom chromosomal changes associated with retinoblastoma, particularly the loss of a chromosome #13 or the deletion of 13q14 was not observed. The establishment of the cell line initially required the presence of bone marrow stromal cells. Morphologically, this cell line grew as a suspension of small round cells in grape-like clusters with periodic "shedding" of single cells. FMC-RB1 could be cloned in soft agar, even in the absence of bone marrow stromal cells as "feeders", making it suitable for a variety of biological studies.

RCH-ACV: a lymphoblastic leukemia cell line with chromosome translocation 1;19 and trisomy 8

A cell line (RCH-ACV) was established from a bone marrow sample of a child with acute lymphoblastic leukemia (ALL). The cell line lacked Epstein-Barr virus nuclear antigen and exhibited a recently described nonrandom chromosome translocation, 1;19, thought to be associated with pre-B-ALL and poor prognosis. Banding studies confirm that the breakpoint of chromosome #19 occurs at p13.3. Cell surface marker analysis using a panel of monoclonal antibodies revealed markers consistent with common ALL phenotype. Although the cells did not show cytoplasmic immunoglobulin, studies of the immunoglobulin gene rearrangement confirmed the pre-B phenotype. This cell line could be of great value to studies of the role of the specific translocation 1;19 in the etiology of pre-B-ALL.

Prenatal diagnosis. A preliminary study of first-trimester chorionic villous biopsy

Biopsy of the developing placenta before the thirteenth gestational week was performed by transcervical cannula aspiration guided by real-time ultrasound in 21 consecutive patients. Chorionic villi were obtained in 20 patients and chromosomal analysis was possible in 19. One significant complication occurred: perforation of one gestational sac in the only patient in the series with a twin pregnancy. More studies are required in order to provide an adequate assessment of the risk--of fetal loss, culture failure and trophoblastic chromosomal abnormalities not representative of the mature fetus--associated with the technique. In practised hands, the procedure may provide a preferable and safe alternative to amino-centesis and fetoscopy for the prenatal diagnosis of genetic defects.

Metamorphosis of retinal exudation following argon laser photocoagulation of retinal telangiectasia

The authors report a case of retinal telangiectasia in which numerous spheroidal, presumably lipid bodies formed within the subretinal space and in instances migrated within the subretinal space and into the vitreous following argon laser photocoagulation to the anomalous retinal vessels.