A paternally derived inverted duplication of 7q with evidence of a telomeric deletion.

We report on a de novo constitutional rearrangement involving the long arm of chromosome 7 in a second trimester fetus with the karyotype of 46,XX, inv dup del (7)(pter-q36::q36-q21.2:) pat. Both a large duplication (q21.2-q36) and a small deletion (within q36) were confirmed by FISH studies. DNA analysis on the family showed that the abnormal chromosome was derived from a single paternal homolog. A mechanism is proposed in light of this finding. The phenotype at autopsy was consistent with reported cases of similar duplications in chromosome 7 in that hydrocephalus, a depressed nasal bridge, low set ears, microretrognathia and a short neck were present.

Physical mapping by PFGE localizes the COL3A1 and COL5A2 genes to a 35-kb region on human chromosome 2.

The genes encoding the alpha 1 chain of Type III collagen (COL3A1) and the alpha 2 chain of Type V (COL5A2) collagen have been mapped to the long arm of human chromosome 2. Linkage analysis in CEPH families indicated that these two genes are close to each other, with no recombination in 37 informative meioses. In the present study, DNA probes from the 3' ends of each gene have been physically mapped by pulsed-field gel electrophoresis. The probes recognized 11 macrorestriction fragments in common, ranging from greater than 1000 kb MluI and NotI fragments to a 35-kb SfiI fragment. Therefore, the COL3A1 and COL5A2 genes appear to exist as a gene cluster on chromosome 2. This is the third example of a collagen gene cluster. Other examples include the COL4A1-COL4A2 genes on chromosome 13q and the COL6A1-COL6A2 genes on chromosome 21q. The physical proximity of these genes may indicate common evolution and/or regulation.

Analysis of DNA polymorphism haplotypes linked to the cystic fibrosis locus in North American black and Caucasian families supports the existence of multiple mutations of the cystic fibrosis gene.

Strong linkage disequilibrium (LD) was found between DNA marker XV2c and the cystic fibrosis (CF) locus (delta = 0.46) and between DNA marker KM19 and CF (delta = 0.67) in 157 CF and 138 normal chromosomes from U.S. Caucasians. DNA haplotypes with nine polymorphic sites were created in 54 Caucasian families. There is a strong LD between the haplotypes and the presence of the mutant CF genes. This implies that the DNA polymorphisms examined are close to the CF gene and that one mutation of the CF gene predominates in the Caucasian population. Haplotype analysis can also be used to refine estimates of CF carrier risk in Caucasians. Data for XV2c and MET markers in 16 American black patients and their families revealed a different haplotype distribution and LD pattern with the CF locus. These data suggest that racial admixture alone does not explain the occurrence of CF in American blacks and that multiple alleles of the CF gene may exist in this population.

The use of polymerase chain reaction to determine fetal RhD status.

OBJECTIVE: Our purpose was (1) to establish the accuracy of a deoxyribonucleic acid amplification method in determination of RhD status in adult blood samples, including weak D variants (previously referred to as Du) and a D mosaic, and (2) to apply the method to determine fetal RhD status in alloimmunized pregnancies. STUDY DESIGN: Twenty-five adult blood samples, including five weak D variants and one D mosaic, were analyzed with a polymerase chain reaction to determine RhD type. The method was then applied to amniotic fluid samples obtained by amniocentesis from three RhD-negative women with known RhD sensitization. RESULTS: RhD type determined by polymerase chain reaction for all adult blood samples agreed with serologic typing results. All weak D variants and the D mosaic gave results consistent with RhD positivity. Fetal RhD status was determined in each of the three alloimmunized pregnancies, and obstetric management decisions were made on the basis of these results. CONCLUSIONS: This polymerase chain reaction method allows rapid and accurate determinations of fetal RhD status by amniocentesis. Fetal blood sampling or serial amniocenteses may be avoided when the fetus is RhD negative, and plans for surveillance and intervention can be confidently made if the fetus is RhD positive. However, before the widespread use of this assay, its sensitivity and specificity must be established. Because weak D variants and a D mosaic demonstrated RhD-positive status by polymerase chain reaction, the method described is applicable to these RhD variants.

A cluster of cystic fibrosis mutations in the first nucleotide-binding fold of the cystic fibrosis conductance regulator protein.

The gene responsible for cystic fibrosis (CF) has recently been identified and is predicted to encode a protein of 1,480 amino acids called the CF transmembrane conductance regulator (CFTR). Several functional regions are thought to exist in the CFTR protein, including two areas for ATP-binding, termed nucleotide-binding folds (NBFs), a regulatory (R) region that has many possible sites for phosphorylation by protein kinases A and C, and two hydrophobic regions that probably interact with cell membranes. The most common CF gene mutation leads to omission of phenylalanine residue 508 in the putative first NBF, indicating that this region is functionally important. To determine whether other mutations occur in the NBFs of CFTR, we determined the nucleotide sequences of exons 9, 10, 11 and 12 (encoding the first NBF) and exons 20, 21 and 22 (encoding most of the second NBF) from 20 Caucasian and 18 American-black CF patients. One cluster of four mutations was discovered in a 30-base-pair region of exon 11. Three of these mutations cause amino-acid substitutions at residues that are highly conserved among the CFTR protein, the multiple-drug-resistance proteins and ATP-binding membrane-associated transport proteins. The fourth mutation creates a premature termination signal. These mutations reveal a functionally important region in the CFTR protein and provide further evidence that CFTR is a member of the family of ATP-dependent transport proteins.

Cloning of the gamma-aminobutyric acid (GABA) rho 1 cDNA: a GABA receptor subunit highly expressed in the retina.

Type A gamma-aminobutyric acid (GABAA) receptors are a family of ligand-gated chloride channels that are the major inhibitory neurotransmitter receptors in the nervous system. Molecular cloning has revealed diversity in the subunits that compose this heterooligomeric receptor, but each previously elucidated subunit displays amino acid similarity in conserved structural elements. We have used these highly conserved regions to identify additional members of this family by using the polymerase chain reaction (PCR). One PCR product was used to isolate a full-length cDNA from a human retina cDNA library. The mature protein predicted from this cDNA sequence in 458 amino acids long and displays between 30 and 38% amino acid similarity to the previously identified GABAA subunits. This gene is expressed primarily in the retina but transcripts are also detected in the brain, lung, and thymus. Injection of Xenopus oocytes with RNA transcribed in vitro produces a GABA-responsive chloride conductance and expression of the cDNA in COS cells yields GABA-displaceable muscimol binding. These features are consistent with our identification of a GABA subunit, GABA rho 1, with prominent retinal expression that increases the diversity and tissue specificity of this ligand-gated ion-channel receptor family.