Prenatal diagnosis in Canada--1990: a review.

This paper presents the results of a detailed study of the genetic prenatal diagnostic services available in Canada in 1990. All 22 genetic centres offering prenatal diagnostic services as well as the 64 laboratories processing samples were surveyed. Data were collected from each to determine what testing was being done, how many women were being tested, for what conditions, and with what outcomes. Also, data on the 35 formal outreach sites were collected. The statistics presented are for the 1990 calendar year. This survey was conducted for the Canadian Royal Commission on New Reproductive Technologies.

Investigation of the origin of variant, truncated estrogen receptor-like mRNAs identified in some human breast cancer biopsy samples.

Variant, smaller sized, estrogen receptor-like mRNAs have been previously cloned and sequenced from human breast cancer biopsy samples. In this study we have found that one variant estrogen receptor-like mRNA, clone 24, which is expressed in only one tumor, consists of sequences from the normal ER gene which is found on chromosome 6 and sequences unrelated to the ER which are found normally on chromosome 12. A more commonly occurring variant estrogen receptor-like mRNA, clone 4, contains sequences from the normal ER gene and LINE-1 sequences. Similar but not identical LINE-1 sequences have been found in some of the intervening sequences of the normal ER gene. The generation of these transcripts may involve either alternative splicing or trans-splicing mechanisms.

Chromosomal localization of a sequence with in vivo activity for initiation of DNA replication.

The genomic fragment containing the sequence of human cDNA clone 343, previously characterized as capable of autonomous replication upon transfection into mammalians cells and occupying a genomic region inclusive of an initiation zone for DNA replication, was mapped on human chromosome 6q22-qter by a combination of in situ hybridization and G-banding. Southern blot hybridization with a panel of human-hamster somatic cells confirmed the location of the 343 gene on chromosome 6. Fragile sites have been mapped to the region at 6q21 and 6q26. Several neoplastic disorders, including melanoma, acute nonlymphocytic leukemia, acute lymphocytic leukemia, and malignant lymphoma, have also exhibited translocations and deletions involving the region 6q21-6q27.

Transmission of the fra(X) haplotype from three nonpenetrant brothers to their affected grandsons.

We report on a family showing transmission of the fra(X) gene by 3 nonpenetrant, fra(X) negative, normally intelligent, full and half-brothers to their affected grandsons. The mothers of the affected boys are obligate carriers, fra(X) negative, and of normal intelligence. This family illustrates the "Sherman Paradox" and is compatible with the predictions of the Laird X-inactivation imprinting model. In addition, molecular and/or cytogenetic studies have enabled at-risk relatives to learn more about their carrier fra(X) status and have allowed for more accurate genetic counselling.

Somatic recombination rather than uniparental disomy suggested as another mechanism by which genetic imprinting may play a role in the etiology of Prader-Willi syndrome.

Six Prader-Willi syndrome (PWS) patients with normal karyotypes and their parents were analyzed to determine the nature of the molecular aberrations present in the proximal region of 15q and to determine the parental origin of the aberrant chromosome 15. In addition, the likelihood that uniparental disomy plays a significant role in the etiology of PWS patients with normal karyotypes was studied. Restriction fragment length polymorphisms (RFLPs) recognized by seven probes [pML34 (D15S9), pTD3-21, pCGS0.9, pCGS1.1 (D15S10), IR4.3 (D15S11), IR10.1 (DS15S12), p189-1 (D15S13), IR39 (D15S18), and CMW-1 (D15S24)] mapping to the Prader-Willi chromosome region (PWCR) and an additional two probes [pMS1-14 (D15S1); the cDNA of neuromedin B] mapping elsewhere on chromosome 15 were analyzed in the six PWS patients and their parents. Copy number of each locus within the PWCR was determined by densitometry. Molecular rearrangements of the proximal region of 15q were observed in all of the six probands and the origin of the aberrant chromosome 15 when determined was consistently paternal in origin. While data obtained from our six patients does not support the mechanism of disomy, results obtained from three of the six patients show more complex rearrangements hypothesized to have resulted from somatic recombination. These rearrangements have resulted in acquired homozygosity and the lack of a paternal allele at various loci within the PWCR. The presence of only a maternal contribution at certain loci as the result of somatic recombination may be another mechanism by which genetic imprinting plays a role in the presentation of the PWS phenotype.

Molecular and clinical overlap of Angelman and Prader-Willi syndrome phenotypes.

The Prader-Willi (PWS) and Angelman syndromes (AS) share the same apparent cytogenetic and molecular lesions of 15q11-13 and yet exhibit distinct clinical phenotypes. The etiology of PWS or AS appears to depend on the parental origin of the aberrant chromosome 15. Substantial clinical overlap has not been reported between deletion-positive PWS and AS patients. In the present study, we report the clinical, cytogenetic, and molecular findings in three AS patients. The first patient is a mentally retarded woman with a visible deletion of 15q11-13 with typical craniofacial, behavioral, and neurologic changes of AS. This patient is hyperphagic, and she is moderately obese for her height. Her hands and feet are small. These manifestations are more characteristic of PWS and not of AS. The molecular studies showed deletions of maternal origin for five distal PWCR loci. The most proximal locus, D15S18, was not deleted. These findings are identical to those found in our third AS patient who does not have any PWS features. To the best of our knowledge, this is the first report of concurrence of hyperphagia with consequent obesity and the AS phenotype in a patient with a del 15(q11-13) of maternal origin. These clinical findings suggest that overlap in the symptoms of PWS and AS can occur. Our second AS patient presents with atypical molecular findings in that he cannot be classed into any of the three proposed sub-groups of AS patients and may be representative of a fourth sub-group of AS patients.

Long-range restriction mapping and linkage analysis of the Prader-Willi chromosome region (PWCR).

In an attempt to elucidate the relationship between genetic alterations at chromosomal bands 15q11.2-12 and the Prader-Willi syndrome (PWS), we have constructed a long-range restriction map of this region using a combination of pulsed-field gel techniques and the infrequently cutting restriction enzymes NotI, MluI, SalI, SfiI, NruI, SacII, and BssHII. Four previously reported probes mapping to 15q11.2-12 and known to be deleted in PWS patients were used to construct the physical map of this region. The loci recognized by these four probes have been localized to a 2600-kb partial SalI restriction fragment and a 3200-kb partial EcoRI restriction fragment. Linkage studies were performed on nine families to estimate the recombination rates between these loci. The calculated lod scores did not indicate significant linkage between any of the four loci. The contrast between the physical distance and the observed recombination frequency suggests that these four loci are located in a recombinational "hot spot."

Detection of molecular rearrangements in Prader-Willi syndrome patients by using genomic probes recognizing four loci within the PWCR.

The Prader-Willi chromosome region (PWCR) in Prader-Willi syndrome patients was analyzed by using genomic DNA probes mapping to 15q11.2-q12. The present report includes analysis of dosage by RFLP and densitometric studies, and analysis of restriction patterns. Twelve Prader-Willi syndrome (PWS) patients were studied: 5 had deletions of 15q11-q13, one had an unbalanced translocation, and 6 were karyotypically normal. Four genomic DNA probes were used: pML34 (D15S9); pTD3-21 (D15S10); IR4-3 (D15S11), a subclone of IR4; and IR10-1 (D15S12), a subclone of IR10 (Donolon et al.: Proc Natl Acad Sci USA 83:4408-4412, 1986). The results presented demonstrate that molecular rearrangements have occurred in 10 of the 12 PWS patients investigated and that the specific rearrangements differ from patient to patient. Patients with apparently similar cytogenetic deletions differ at the molecular level with deletions and/or duplications of various loci. The present study reports molecular alterations within the PWCR in PWS patients reported as cytogenetically normal. However, the 6 karyotypically normal patients are a heterogeneous group with molecular rearrangements ranging from none detected to deletions and/or duplications. These molecular studies suggest that a physical disruption of the PWCR causes the PWS not only in those patients reported to have a cytogenetic aberration but also in those identified as apparently karyotypically normal. The question remains as to whether the PWS patients in whom a molecular abnormality has not been detected have an autosomal recessive form of PWS, a molecular disruption which has not yet been detected, or another mechanism producing an apparently identical phenotype. The order of the 4 loci on chromosome 15 is hypothesized to be cen----D15S9----D15S12----D15S11----D15S10.

Chromosomal localization and structure of the human P1 protamine gene.

The human P1 protamine gene and mRNA were amplified with the use of the polymerase chain reaction and cloned into PTZ19R. The sequences were determined which revealed the presence of an intron. Southern and Northern hybridization analyses showed that the gene was single copy and that the mRNA was approximately 450 bases long. The gene was mapped to chromosome 16 with the use of a somatic cell hybrid panel and localized to the 21 region of the q arm by in situ hybridization of the human P1 protamine probe to human metaphase chromosomes.