S. Jeremiah

The gene for human complement component C9 mapped to chromosome 5 by polymerase chain reaction

The gene for human complement component C9 has been mapped to chromosome 5. This was achieved by using a novel application of the polymerase chain reaction to amplify specifically the human C9 gene on a background of rodent DNA in somatic cell hybrids. The assignment to chromosome 5 was confirmed by in situ hybridization to human metaphase chromosomes, giving a regional localization of 5p13.

Assignment of the human locus determining phosphoglycolate phosphatase (PGP) to chromosome 16

The segregation of human phosphoglycolate phosphatase has been studied in 52 independent human-rodent hybrids and 69 subclones. The results suggest that human PGP is on chromosome 16. Family data suggest that PGP is not close to 16qh or alpha Hp. The most likely regional assignment for PGP would appear to be 16p13 or 16p12, but a site on 16q cannot be entirely excluded. New data on 16qh and alpha Hp suggest that the male recombination fraction between these loci is about 0.2.

A mutation screen of the TSC1 gene reveals 26 protein truncating mutations and 1 splice site mutation in a panel of 79 tuberous sclerosis patients

The entire coding region of the TSC1 gene has been screened for mutations in 79 unrelated patients with tuberous sclerosis. Causative mutations have been found in 27 of these patients and five other variations in the gene have been identified. 26 of the mutations are predicted to cause premature truncation of the protein product of the gene and one mutation is in a splice site. The mutation screen has revealed that TSC1 mutations are rarer in sporadic tuberous sclerosis patients than in familial cases. We have also found that the only previously described case of non‐penetrance can no longer be described as such, and that a single ungual fibroma is not necessarily diagnostic of tuberous sclerosis, important findings for the genetic counselling of tuberous sclerosis patients.

The assignment of the genes coding for human complement components C6 and C7 to chromosome 5

A panel of 19 somatic cell hybrids was tested for the presence of human sequences coding for complement components C6 and C7 by restriction enzyme digestion and Southern blots probed with human C6 and C7 cDNA probes. C7 was also detected by amplifying part of the human gene in hybrid DNA using the polymerase chain reaction. Detection of human C6 and C7 was completely correlated with the presence of chromosome 5.

Mapping studies on human mitochondrial glutamate oxaloacetate transaminase

Data from six primary hybrids and twenty‐two subclones have confirmed the assignment of the mitochondrial form of glutamate oxaloacetate transaminase to chromosome 16. Family studies have provided independent confirmation of this and have suggested the gene order PGP‐16qh‐GOT2‐HP. These studies were made easier by the development of a new stain for the detection of GOT activity.

Assignment of the human nicotinic acetylcholine receptor genes: the alpha and delta subunit genes to chromosome 2 and the beta subunit gene to chromosome 17

The chromosomal assignments of the genes coding for the alpha, beta and delta subunits of the human nicotinic acetylcholine receptor have been determined from a panel of somatic cell hybrids and by direct in situ hybridization. The results localize CHRNA to 2q24‐2q32. CHRNB to 17p11 17p12, and CHRND to chromosome 2q33‐2qter.

Differences in genetic stability between human cell lines from patients with and without lymphoreticular malignancy

Isozymes determined by 11 loci have been examined in 137 human lymphoblastoid lines of various origins with a view to determining their phenotypic stability in culture. Lines of normal origin are stable and at these loci are phenotypically identical to the individuals from whom they are derived. Lymphomas and some lines from patients with leukaemias show a tendency to increased apparent homozygosity, presumably resulting from loss of expression of one or other allele during culture. Taken together with the cytogenetic evidence this suggests that progressive loss of functional parts of the genome with time in culture is a characteristic of lines derived from malignant lymphoid cells.

Deficiency of malic enzyme: a possible marker for malignancy in lymphoid cells

Soluble malic enzyme (MES) has been examined in long‐term human lymphoid cell lines cultured from 101 individuals. In 65 out of 66 lines derived from people without lymphoreticular malignancy the enzyme was very active. Lines established from 35 individuals with various forms of lymphoreticular malignancy were also examined, including in some cases more than 1 line derived from the same patient. In all cases where the cell line was thought to be derived from normal cells MES was active, but in 27 out of 29 lines thought to be derived from malignant cells (from 25 patients) MES was not detected. In the case of two patients with chronic lymphatic leukaemia ‘normal’ lines active for malic enzyme, and ‘leukaemic’ lines lacking malic enzyme, had been cultured from the same individual. Preliminary investigations of the lack of malic enzyme in somatic cell hybrids derived from lymphoma and leukaemia cell lines are compatible with an alteration at the level of the structural locus MES on chromosome 6. However, the restoration of MES activity in one line by fusion with mouse teratocarcinoma cells suggests that the alteration may be of a regulatory nature.

The biochemical genetics of human γ-aminobutyric acid transaminase

1. Two methods have been devised for the detection after electrophoresis of γ‐aminobutyric acid transaminase (GABAT) isozymes.

Chromosomal localisation of genes coding for human and mouse liver cytosolic cysteine dioxygenase

A panel of 22 hybrids was tested for the presence of the gene coding for human cysteine dioxygenase (CDO) by using human specific oligonucleotide primers in the polymerase chain reaction. Detection of human CDO completely correlated with the presence of human chromosome 5. A human total genome cosmid library was screened with a PCR product from the coding region of human CDO cDNA and the two positive clones identified were used in fluorescent in situ hybridisation (FISH) analysis on metaphase chromosome spreads. Fluorescent signals were seen on chromosome 5q22–23. Interspecific backcross mapping in the mouse indicated that Cdo, the mouse homologue of CDO, is situated in the central region of mouse chromosome 18 which shares a region of homology with human chromosome 5.