Germline mismatch repair (MMR) gene analyses from English NHS regional molecular genomics laboratories 1996-2020: development of a national resource of patient-level genomics laboratory records

OBJECTIVE

To describe national patterns of National Health Service (NHS) analysis of mismatch repair (MMR) genes in England using individual-level data submitted to the National Disease Registration Service (NDRS) by the NHS regional molecular genetics laboratories.

DESIGN

Laboratories submitted individual-level patient data to NDRS against a prescribed data model, including (1) patient identifiers, (2) test episode data, (3) per-gene results and (4) detected sequence variants. Individualised per-laboratory algorithms were designed and applied in NDRS to extract and map the data to the common data model. Laboratory-level MMR activity audit data from the Clinical Molecular Genetics Society/Association of Clinical Genomic Science were used to assess early years' missing data.

RESULTS

Individual-level data from patients undergoing NHS MMR germline genetic testing were submitted from all 13 English laboratories performing MMR analyses, comprising in total 16 722 patients (9649 full-gene, 7073 targeted), with the earliest submission from 2000. The NDRS dataset is estimated to comprise >60% of NHS MMR analyses performed since inception of NHS MMR analysis, with complete national data for full-gene analyses for 2016 onwards. Out of 9649 full-gene tests, 2724 had an abnormal result, approximately 70% of which were (likely) pathogenic. Data linkage to the National Cancer Registry demonstrated colorectal cancer was the most frequent cancer type in which full-gene analysis was performed.

CONCLUSION

The NDRS MMR dataset is a unique national pan-laboratory amalgamation of individual-level clinical and genomic patient data with pseudonymised identifiers enabling linkage to other national datasets. This growing resource will enable longitudinal research and can form the basis of a live national genomic disease registry.

Diverse presentations of cutaneous mosaicism occur in CYLD cutaneous syndrome and may result in parent-to-child transmission

Background

Clusters of rare cylindroma or spiradenoma tumors are a recurrent clinical presentation, yet conventional genetic testing results in individuals with these tumors are frequently normal.

Objective

To determine if genetic mosaicism accounts for such cases.

Methods

A study of 6 cases from a series of 55 patients who met criteria for diagnostic gene testing for pathogenic CYLD variants over a 5-year period (2012-2017) was performed. A novel genetic assay was used to study DNA from peripheral blood leukocytes and, where possible, matched skin and tumor tissue.

Results

Two patients had mosaic pathogenic CYLD variants in both the blood and skin. One of these patients transmitted a pathogenic variant to her daughter, and we report the novel phenotype of a contiguous gene deletion syndrome involving CYLD. Two patients had recurrent pathogenic variants in skin tumors from a single cluster but none detectable in the blood.

Limitations

The remaining 2 patients had clinical features of mosaicism, but these cases were not solved with the assays used because of a lack of access of fresh tumor tissue.

Conclusion

Genetic mosaicism should be considered in patients presenting with clustered cylindromas, because this may inform genetic testing and counseling of these patients.

Bi-allelic Loss-of-Function CACNA1B Mutations in Progressive Epilepsy-Dyskinesia

The occurrence of non-epileptic hyperkinetic movements in the context of developmental epileptic encephalopathies is an increasingly recognized phenomenon. Identification of causative mutations provides an important insight into common pathogenic mechanisms that cause both seizures and abnormal motor control. We report bi-allelic loss-of-function CACNA1B variants in six children from three unrelated families whose affected members present with a complex and progressive neurological syndrome. All affected individuals presented with epileptic encephalopathy, severe neurodevelopmental delay (often with regression), and a hyperkinetic movement disorder. Additional neurological features included postnatal microcephaly and hypotonia. Five children died in childhood or adolescence (mean age of death: 9 years), mainly as a result of secondary respiratory complications. CACNA1B encodes the pore-forming subunit of the pre-synaptic neuronal voltage-gated calcium channel Ca_v2.2/N-type, crucial for SNARE-mediated neurotransmission, particularly in the early postnatal period. Bi-allelic loss-of-function variants in CACNA1B are predicted to cause disruption of Ca²⁺ influx, leading to impaired synaptic neurotransmission. The resultant effect on neuronal function is likely to be important in the development of involuntary movements and epilepsy. Overall, our findings provide further evidence for the key role of Ca_v2.2 in normal human neurodevelopment.

Genotype-phenotype correlations in Cornelia de Lange syndrome: Behavioral characteristics and changes with age

Cornelia de Lange syndrome (CdLS) is a multisystem genetic disorder associated with unusual facial features, limb abnormalities, a wide range of health conditions, and intellectual disability. Mutations in five genes that encode (SMC1A, SMC3, RAD21) or regulate (NIPBL, HDAC8) the cohesin complex have been identified in up to 70% of individuals. Genetic cause remains unknown for a proportion of individuals. There is substantial heterogeneity in all aspects of CdLS but very little is known about what predicts phenotypic heterogeneity. In this study, we evaluated genotype-phenotype associations in 34 individuals with CdLS. Participants with NIPBL mutations had significantly lower self help skills and were less likely to have verbal skills relative to those who were negative for the NIPBL mutation. No significant differences were identified between the groups in relation to repetitive behavior, mood, interest and pleasure, challenging behavior, activity, impulsivity, and characteristics of autism spectrum disorder whilst controlling differences in self help skills. Significant correlations indicating lower mood, interest and pleasure, and increased insistence on sameness with older age were identified for those who were NIPBL mutation positive. The findings suggest similarities in the behavioral phenotype between those with and without the NIPBL mutation once differences in self help skills are controlled for. However, there may be subtle differences in the developmental trajectory of these behaviors according to genetic mutation status in CdLS.

Incidence and outcomes for adults diagnosed with acute myeloid leukemia in the north of England: a real world study

We conducted a retrospective population-based study of patients diagnosed with acute myeloid leukemia (AML) in northern England (population 3.1 million) in order to assess the impact of age and genetics on outcome. Four hundred and sixteen patients were diagnosed with AML, between 2007 and 2011. In those aged ≤60 years (n = 20) with acute promyelocytic leukemia (APL) overall survival (OS) was 100%. For non-APL patients aged ≤60 years, OS for those with favorable, intermediate and adverse cytogenetics was not reached, 17 and 9.8 months, respectively (p = 0.0001). Of particular note, intensively treated patients aged >60 years with intermediate cytogenetics and FLT3-/NPM1+ status had a five-year survival of 60% versus median OS of 11 months for other subsets (p = 0.04). Population-based studies reduce selection bias and have utility in studying rarer diseases, particularly in populations that recruit poorly to trials. The highly favorable outcome in our subgroup of intensively-treated FLT3-/NPM1+ older patients merits further study.

Large-scale discovery of novel genetic causes of developmental disorders

Despite three decades of successful, predominantly phenotype-driven discovery of the genetic causes of monogenic disorders, up to half of children with severe developmental disorders of probable genetic origin remain without a genetic diagnosis. Particularly challenging are those disorders rare enough to have eluded recognition as a discrete clinical entity, those with highly variable clinical manifestations, and those that are difficult to distinguish from other, very similar, disorders. Here we demonstrate the power of using an unbiased genotype-driven approach to identify subsets of patients with similar disorders. By studying 1,133 children with severe, undiagnosed developmental disorders, and their parents, using a combination of exome sequencing and array-based detection of chromosomal rearrangements, we discovered 12 novel genes associated with developmental disorders. These newly implicated genes increase by 10% (from 28% to 31%) the proportion of children that could be diagnosed. Clustering of missense mutations in six of these newly implicated genes suggests that normal development is being perturbed by an activating or dominant-negative mechanism. Our findings demonstrate the value of adopting a comprehensive strategy, both genome-wide and nationwide, to elucidate the underlying causes of rare genetic disorders.

CYLD GeneticTesting for Brooke-Spiegler Syndrome, Familial Cylindromatosis and Multiple Familial Trichoepitheliomas

The clinical presentation of multiple, rare, skin appendage tumours called cylindromas has been attributed to germline mutations in the tumour suppressor gene <i>CYLD</i> (OMIM 605018). Brooke-Spiegler Syndrome (BSS), familial cylindromatosis (FC) and multiple familial trichoepitheliomas (MFT) (OMIM #605041, #132700, #601606 respectively) differ due to the types of other skin appendage tumour seen together with cylindroma, such as spiradenoma and trichoepithelioma. Previously thought to be separate entities, they are now viewed as allelic variants with overlapping phenotypes, supported by mutation analysis of <i>CYLD</i> . The conditions display autosomal dominant inheritance and affected individuals develop multiple benign skin tumours most commonly on the head and neck. <i>CYLD</i> testing can be performed using PCR and Sanger sequencing for patients with: 1. Multiple cylindromas, spiradenomas or trichoepitheliomas. 2. A single cylindroma, spiradenoma or trichoepithelioma and an affected first-degree relative with any of these tumours. 3. An asymptomatic family member at 50% risk with a known mutation in the family.

Pilot of BRAF mutation analysis in indeterminate, suspicious and malignant thyroid FNA cytology

BACKGROUND

BRAF V600E mutation has been reported to show a high specificity for papillary thyroid carcinoma (PTC). Using this marker to upgrade 'indeterminate' or 'suspicious' thyroid fine needle aspiration (FNA) cytology to 'malignant' could potentially allow one-stage therapeutic total thyroidectomy.

METHODS

For a 14-month period, FNA cytology specimens in the Thy3-5 categories, which are the UK equivalents of indeterminate (Thy3a, atypical; Thy3f, follicular), suspicious for malignancy (Thy4) and malignant (Thy5) in the Bethesda System, underwent BRAF mutation testing by melt curve analysis. The results were correlated with histology.

RESULTS

We tested 123 cytology specimens of which 12 (9.8%) failed. The BRAF mutation rate in the remainder was 16.2% (18/111), with 93 showing the wild-type. Seventeen mutations were V600E and one was non-V600E. The rate of mutation increased significantly (P < 0.0001 if Thy3a and Thy3f were combined) with the cytology category: 1/42 Thy3a (2.4%), 1/36 Thy3f (2.8%), 4/15 Thy4 (26.7%), 12/18 Thy5 (66.7%). All BRAF mutations correlated with PTC on histology, except for one recurrent PTC without histology. One mutation-positive case with Thy3a cytology showed the target lesion to be a 10-mm follicular adenoma on histology with an immediately adjacent 4-mm micro-PTC, in a patient who did not require total thyroidectomy.

CONCLUSION

BRAF mutational analysis by melt curve analysis is feasible in routine thyroid cytology, and in our series had a 100% specificity for PTC in subsequent histology. The application of BRAF analysis could be useful for indeterminate cytology, but we suggest that it would be most appropriate and cost-effective for Thy4/suspicious cases, for which it could enable one-stage therapeutic surgery in the context of multidisciplinary discussion. In contrast, the sensitivity is low and there is no role for avoiding diagnostic thyroid surgery if wild-type BRAF is found.

Phenotypic variations of cartilage hair hypoplasia: granulomatous skin inflammation and severe T cell immunodeficiency as initial clinical presentation in otherwise well child with short stature

We report a child with short stature since birth who was otherwise well, presenting at 2.8 years with progressive granulomatous skin lesions when diagnosed with severe T cell immunodeficiency. When previously investigated for short stature, and at the time of current investigations, she had no radiological skeletal features characteristics for cartilage hair hypoplasia, but we found a disease causing RMRP (RNase mitochondrial RNA processing endoribonuclease) gene mutation. Whilst search for HLA matched unrelated donor for haematopoietic stem cell transplantation (HSCT) was underway, she developed rapidly progressive EBV-related lymphoproliferative disorder requiring laparotomy and small bowel resection, and was treated with anti-B cell monoclonal antibody and eventually curative allogeneic HSCT. Screening for RMRP gene mutations should be part of immunological evaluation of patients with ‘severe and/or combined’ T cell immunodeficiency of unknown origin, especially when associated with short stature and regardless of presence or absence of radiological skeletal features.

Functional polymorphisms affecting the clinically important arginine-137 residue of AVPR2 do not influence serum sodium concentration at the population level

The protein product of the AVPR2 gene, coding for the arginine vasopressin receptor type 2, is essential for vasopressin-dependent concentration of the urine. The arginine residue at position 137 in the protein product of this gene is uniquely pivotal for function. The R137H mutant inactivates the receptor conferring congenital nephrogenic diabetes insipidus, whereas activating mutations at this same residue (i.e., R137C and R137L) confer pathological water retention in the nephrogenic syndrome of inappropriate antidiuresis. These mutations were discovered in human subjects with conspicuous phenotypes in clinical water balance. Prevalence of these polymorphisms among asymptomatic individuals has not been assessed, nor has their contribution to broad interindividual variation in serum sodium concentration; no data addressing minor allele frequency are available. We genotyped two large cohorts using a validated high-throughput Pyrosequencing-based assay that we designed to capture the totality of pathological variation at this important residue. In the Osteoporotic Fractures in Men (MrOS) Study, all participants were male (i.e., hemizygous for AVPR2 gene on the X-chromosome), and participants were oversampled at the extremes of the population distribution for serum sodium concentration. In the Offspring Cohort of the Framingham Heart Study, male and female participants were genotyped. No pathological variants affecting R137 were detected among the 5,142 AVPR2 alleles successfully genotyped. Even at the population extremes of serum sodium distribution, we estimate minor allele frequency < 0.06%. We conclude that these disease-associated variants are exceedingly uncommon and do not contribute broadly to interindividual variability in serum sodium concentration or to its heritability.

Utility of genetic testing in suspected familial cranial diabetes insipidus

Aim

Differentiating familial cranial diabetes insipidus (CDI) from primary polydipsia can be difficult. We report the diagnostic utility of genetic testing as a means of confirming or excluding this diagnosis.

Patient and methods

The index case presented at 3 months with polydipsia. He was diagnosed with familial CDI based on a positive family history combined with what was considered to be suspicious symptomatology and biochemistry. He was treated with desmopressin (DDAVP) but re-presented at 5 months of age with hyponatraemia and the DDAVP was stopped. Gene sequencing of the vasopressin gene in father and his offspring was undertaken to establish the underlying molecular defect.

Results

Both father and daughter were found to have the pathogenic mutation c.242T>C (p.Leu81Pro) in exon 2 of the AVP gene consistent with a diagnosis of familial diabetes insipidus. The index case did not have the pathogenic mutation and the family could be reassured that he would not require intervention with DDAVP.

Conclusions

Gene sequencing of AVP gene can have a valuable role in predicting whether or not a child is at risk of developing CDI in future. This can help to prevent family uncertainty and unnecessary treatment with its associated risks.

Learning points

Differentiating patients with familial cranial diabetes insipidus from those with primary polydipsia is not always straightforward.

Molecular genetic analysis of the vasopressin gene is a valuable way of confirming or refuting a diagnosis of familial CDI in difficult cases and is a valuable way of identifying individuals who will develop CDI in later childhood. This information can be of great value to families.

Is CFTR-delF508 really absent from the apical membrane of the airway epithelium?

BACKGROUND

Understanding where mutant CFTR is localised in airway epithelia is essential in guiding the best therapeutic approach to correct the dysfunction of the CFTR protein. The widely held paradigm is that CF patients harbouring the commonest mutation, CFTR-delF508, trap CFTR within the endoplasmic reticulum and target it for degradation. However there are conflicting reports concerning expression and localisation of CFTR-delF508 in lung tissue. To attempt to resolve this fundamental issue we developed a novel approach to measure CFTR-delF508 in the lower airways of patients who have undergone lung transplantation for advanced CF. By sampling CF and non-CF epithelium simultaneously from the same individual, confounding factors of different airway microenvironments which may have influenced previous observations can be overcome.

METHODS

Epithelia sampled by bronchial brushing above (CF) and below (non-CF) the bronchial anastomosis were stained for CFTR and the localisation and level of expression assessed (n = 12).

RESULTS

There was no significant difference in the proportion of tall columnar cells showing CFTR immunostaining as a discrete band at the apical membrane in cells harbouring the CFTR-delF508 mutation compared to non-CF cells (p = 0.21, n = 12). However, the amount of CFTR expressed at the apical surface was reduced by ∼50% in CF cells compared to non-CF cells (p = 0.04, n = 5).

CONCLUSIONS

Our novel observation challenges the prevailing paradigm that CFTR is essentially absent from the apical membrane of respiratory cells harbouring the CFTR-delF508 mutation. Moreover, it raises the possibility that the new generation of CFTR potentiators may offer a realistic therapeutic option for CF patients.

Thirst perception and arginine vasopressin production in a kindred with an activating mutation of the type 2 vasopressin receptor: the pathophysiology of nephrogenic syndrome of inappropriate antidiuresis

BACKGROUND

Activating mutations of the vasopressin receptor gene on the X chromosome cause the nephrogenic syndrome of inappropriate antidiuresis (NSIAD). We describe a male child who presented with persistent hyponatraemia and whose mother was also found to be hyponatraemic. She had learnt to avoid excess fluid consumption because of associated malaise. Both individuals had a subnormal ability to excrete a water load with mother also demonstrating a heightened sense of thirst at low serum osmolalities.

RESULTS

Mother and child were found to have the previously characterised activating mutation (p.Arg137Cys) of the arginine vasopressin receptor type 2 gene (AVPR2), but had measurable levels of AVP when hyponatraemic.

CONCLUSIONS

We conclude that female carriers of activating mutations of the vasopressin receptor are susceptible to hyponatraemia and therefore need to be provided with advice regarding fluid intake. An altered thirst perception may increase susceptibility to hyponatraemia. We confirm that the presence of measurable amounts of AVP in patients with hyponatraemia does not exclude the diagnosis of NSIAD.

Quantitative assessment of mixed chimerism in allogeneic stem cell transplant patients: a comparison of molecular genetic and cytogenetic approaches

After allogeneic stem cell transplantation, dual donor and recipient populations may be present. Donor/recipient ratio changes over time may predict clinical outcome: accurate measurement of these changes are needed. Chimerism may be measured by XY-fluorescence in situ hybridization for donor/recipient sex mismatch, or polymerase chain reaction amplification of short tandem repeat loci with donor/recipient sex match. Patients were monitored by each method. Additionally, mononuclear cells from 2 sex-mismatched individuals were mixed and analyzed using both methods. Each gave concordant estimates of patient chimerism and discriminated cell population ratios in mixed blood. We conclude that cytogenetic and molecular methods give accurate donor chimerism estimates.

Characteristics of cattle movements in Britain – an analysis of records from the Cattle Tracing System

This paper reviews the main temporal and spatial characteristics of cattle movements in Britain, based on an analysis of records in the British Cattle Movement Service's Cattle Tracing System (CTS) database, focusing on the period 2001 to 2003, during which notification of cattle movements was mandatory. Movements vary weekly and seasonally according to the production cycle, with peaks in late spring (April) and early autumn (October), and an average 1·63 million farm-to-farm movements per month, equivalent to 19·6 million per annum. The geographical distribution of these movements appears to be relatively stable from year to year, with the great majority of animals moving less than 100 km per journey, although many tens of thousands move over far greater distances of up to 1000 km. The procedures developed to extract, match, geo-reference, analyse and display movement records have greatly enhanced the utility of the CTS database, in that it is now feasible to assess, monitor and mapthe spatial dynamics and geographical distribution of cattle movements, and provide this information in standardized format on a regular basis.

Atypical haemolytic uraemic syndrome associated with a hybrid complement gene

BACKGROUND

Sequence analysis of the regulators of complement activation (RCA) cluster of genes at chromosome position 1q32 shows evidence of several large genomic duplications. These duplications have resulted in a high degree of sequence identity between the gene for factor H (CFH) and the genes for the five factor H-related proteins (CFHL1-5; aliases CFHR1-5). CFH mutations have been described in association with atypical haemolytic uraemic syndrome (aHUS). The majority of the mutations are missense changes that cluster in the C-terminal region and impair the ability of factor H to regulate surface-bound C3b. Some have arisen as a result of gene conversion between CFH and CFHL1. In this study we tested the hypothesis that nonallelic homologous recombination between low-copy repeats in the RCA cluster could result in the formation of a hybrid CFH/CFHL1 gene that predisposes to the development of aHUS.

METHODS AND FINDINGS

In a family with many cases of aHUS that segregate with the RCA cluster we used cDNA analysis, gene sequencing, and Southern blotting to show that affected individuals carry a heterozygous CFH/CFHL1 hybrid gene in which exons 1-21 are derived from CFH and exons 22/23 from CFHL1. This hybrid encodes a protein product identical to a functionally significant CFH mutant (c.3572C>T, S1191L and c.3590T>C, V1197A) that has been previously described in association with aHUS.

CONCLUSIONS

CFH mutation screening is recommended in all aHUS patients prior to renal transplantation because of the high risk of disease recurrence post-transplant in those known to have a CFH mutation. Because of our finding it will be necessary to implement additional screening strategies that will detect a hybrid CFH/CFHL1 gene.

ABCA12 is the major harlequin ichthyosis gene

Harlequin ichthyosis (HI) is the most severe form of autosomal-recessive, congenital ichthyosis. Affected infants have markedly impaired barrier function and are more susceptible to infection. Abnormalities in the localization of epidermal lipids as well as abnormal lamellar granule formation are features of HI skin. Previously, we and others have shown that mutations in the ABCA12 gene encoding an adenosine triphosphate-binding cassette (ABC) transporter underlie the skin disease HI. In this study, we have sequenced the ABCA12 gene in an additional 14 patients and show that all contain mutations, with the majority being either nonsense substitution or frameshift mutations. Eleven HI patients had bi-allelic ABCA12 mutations, whereas in the remaining three HI patients in this study, ABCA12 mutations were detected on only one allele by sequencing. In addition, the one patient from the previous study where no sequence mutations were detected was screened for heterozygous deletions. A combination of oligonucleotide arrays, multiplex PCR analysis and single-nucleotide polymorphism genotyping revealed a heterozygous intragenic deletion in exon 8. These mutation data establish ABCA12 as the major HI gene.

Cattle movements and bovine tuberculosis in Great Britain

For 20 years, bovine tuberculosis (BTB) has been spreading in Great Britain (England, Wales and Scotland) and is now endemic in the southwest and parts of central England and in southwest Wales, and occurs sporadically elsewhere. Although its transmission pathways remain poorly understood, the disease's distribution was previously modelled statistically by using environmental variables and measures of their seasonality. Movements of infected animals have long been considered a critical factor in the spread of livestock diseases, as reflected in strict import/export regulations, the extensive movement restrictions imposed during the 2001 foot-and-mouth disease outbreak, the tracing procedures after a new case of BTB has been confirmed and the Government's recently published strategic framework for the sustainable control on BTB. Since January 2001 it has been mandatory for stock-keepers in Great Britain to notify the British Cattle Movement Service of all cattle births, movements and deaths. Here we show that movements as recorded in the Cattle Tracing System data archive, and particularly those from areas where BTB is reported, consistently outperform environmental, topographic and other anthropogenic variables as the main predictor of disease occurrence. Simulation distribution models for 2002 and 2003, incorporating all predictor categories, are presented and used to project distributions for 2004 and 2005.

The rise and fall of the Aldabran giant tortoise population

At the end of the 19th century, after prolonged and extensive harvesting, indigenous giant tortoises had been eliminated from all islands in the Indian Ocean, except Aldabra atoll, where only a few survived. With greatly reduced levels of exploitation during the 20th century, the population recovered to a revised estimated total of 129,000 in 1973-1974, when the first sample census was conducted. A repeat census in 1997 revealed a highly significant reduction in numbers over the past 24 years to an estimated total of 100,000. The great majority of tortoises are still found at relatively high density in south-eastern Grande Terre, where the number of animals has declined by more than one-third. In contrast, low-density subpopulations on Malabar and Picard have almost doubled in size, but they represent less than 5% of the total population. Corroborative evidence for the crash in the Grande Terre subpopulation comes from two independent observations: a significant increase in tortoise mortality; and a significant decline in tortoise counts on long-term population monitoring transects. These population changes are attributed to natural population regulatory mechanisms, exacerbated by low rainfall years in the period 1980-1997, including two consecutive years of below average rainfall in 1995-1996 and 1996-1997.

H4 acetylation, XIST RNA and replication timing are coincident and define x;autosome boundaries in two abnormal X chromosomes

The inactive X (Xi) differs from its active homologue (Xa) in a number of ways, including increased methylation of CpG islands, replication late in S phase, underacetylation of histone H4 and association with XIST RNA. Global changes in DNA methylation occur relatively late in development, but the other properties all change during or shortly after the establishment of Xi and may play a role in the mechanism by which an inactive chromatin conformation spreads across most of the chromosome. In the present report, we use two human X;autosome translocation chromosomes to study the spreading of inactive X chromatin across X;autosome boundaries. In one of these chromosomes, t(X;6), Xp distal to p11.2 is replaced by 6p21.1-6pter and, in the other, ins(X;16), a small fragment derived from 16p13 is inserted into the distal third of Xq. In lymphoid cells from patients carrying these translocations in an unbalanced form, Xi was shown by HUMARA assay to be derived exclusively [t(X:6)] or predominantly [ins (X;16)] from the derived X chromosome. We used a combination of immunolabelling and RNA/DNA fluorescence in situ hybridization to define the distribution of XIST RNA, deacetylated H4 and late-replicating DNA across the two derived X chromosomes in inactive form. Within the limits of the cytogenetic techniques employed, the results show complete coincidence of these three parameters, with all three being excluded from the autosomal component of the derived X chromosome.

Highly polymorphic dinucleotide repeat at the NF2 gene

A highly polymorphic CA repeat was identified in a cosmid containing the 5' end of the NF2 tumour suppressor gene. This marker has proved useful in presymptomatic diagnosis in affected families.

Diagnostic issues in a family with late onset type 2 neurofibromatosis

We report a family with type 2 neurofibromatosis and late onset tumours. Five members of this family have developed hearing loss late in life, two of whom have only been shown to have the diagnosis in their seventies, and three other obligate gene carriers died undiagnosed at 64, 72, and 78 years of age. A missense mutation at the C-terminal end of the NF2 protein has been identified in this family and segregates with disease. The use of highly polymorphic markers for predictive testing is also shown. There appears to be an autosomal dominant form of spinocerebellar degeneration which is segregating separately to NF2 in this family, which created a diagnostic dilemma.

Eleven novel mutations in the NF2 tumour suppressor gene

Eleven novel mutations were identified in the NF2 tumour suppressor gene in a panel of British NF2 patients. Screening was performed using a combination of heteroduplex and single-strand conformation polymorphism analysis on polymerase chain reaction amplified material.

A mutation in the neurofibromatosis type 2 tumor-suppressor gene, giving rise to widely different clinical phenotypes in two unrelated individuals

We have sought mutations in the recently identified neurofibromatosis type 2 (NF2) tumor-suppressor gene in a large panel of NF2 patients, using PCR-based SSCP and heteroduplex analysis, followed by cloning and sequencing of appropriate PCR products. Two unrelated NF2 patients were found to have identical nonsense mutations caused by a C-to-T transition in a CpG dinucleotide that is a potential mutational hot spot in the NF2 tumor-suppressor gene. Unexpectedly, the two individuals had widely different clinical phenotypes, representing the severe Wishart and mild Gardner clinical subtypes. Analysis of DNA samples from different tissues of the mildly affected patient suggests that he is a somatic mosaic for the mutation.

Germline mutations in the neurofibromatosis type 2 tumour suppressor gene

The recent identification of the NF2 tumour suppressor gene has enabled large scale screening for pathological mutations in the gene. We have sought germline mutations in the NF2 gene by SSCP and heteroduplex analysis of cDNA and genomic DNA samples followed by cloning and sequencing of mutant alleles. In the present report we describe 11 putative pathological mutations, including five nonsense mutations, three short insertions or deletions causing frameshifts and three missense mutations. Most stop mutations and frameshift mutations were found in individuals expressing a severe phenotype while one of the three missense mutations was associated with a mild phenotype. Four unrelated NF2 patients of the 93 tested were found to have identical nonsense mutations caused by a C to T transition (C169) in a CpG dinucleotide, which is a potential mutational hotspot in the NF2 tumour suppressor gene.

An intron-containing tRNAArg gene within a large cluster of human tRNA genes

The insert within lambda Ht363, a recombinant selected from a bank of human genomic DNA cloned in lambda Ch4A, is described. Southern blot hybridization with a mixed tRNA[32P]pCp probe revealed the presence of four tRNA genes, which were shown to represent further copies of genes previously identified as a solitary tRNAGly gene and as a three gene cluster on two different recombinants. In vitro transcription of a fragment containing the three gene cluster revealed the presence of a further pol III gene, which was shown to be that for a tRNAArgTCT. This gene contains a 15 bp intron, the presence of which presumably prevented its detection on Southern blots by tRNA hybridisation. The gene is present in the previously reported cluster and occurs in higher copy number (> 7) in other arrangements in the genome. Most of the copies of the gene have related intron sequences.

Screening for noninsulin dependent diabetes mellitus and impaired glucose tolerance in a Dunedin general practice--is it worth it?

AIMS

the main aims of this study were to investigate the feasibility of screening for noninsulin dependent diabetes mellitus (NIDDM) and impaired glucose tolerance (IGT) in general practice and to compare random blood glucose measurements with the two hour oral glucose tolerance test as screening methods.

METHODS

one thousand, one hundred and eighty-four people aged 39-79 years who were registered with two general practitioners were invited to be screened using a random blood glucose test. Subjects who had a random test and were aged 39-69 years were subsequently invited to have a two hour oral glucose tolerance test (OGTT). Those subjects who had a raised random blood glucose level or a raised fasting and/or two hour plasma glucose level according to WHO criteria, were invited back for two additional OGTTs.

RESULTS

the overall response rate for the random blood glucose testing was 67%. Forty-seven percent of those aged 50-69 years and 35% of those aged 39-49 years completed one OGTT. A number of people with high random blood glucose levels had normal OGTTs which suggests that the risk of a false positive result from the random test is high. In addition, a number of false negative results from the random test were identified. A total of 20 people were found to have IGT, although only three of these were identified from the random test which confirms the necessity of administering an OGTT for the identification of IGT. Only 44% of those identified with IGT from a single test remained in the IGT category after repeat testing. The prevalence of NIDDM and IGT for people aged 39-69 years was 4.4%.

CONCLUSIONS

the random glucose test did identify people with NIDDM however this test was found to be an insensitive technique for identifying IGT. A number of cases of NIDDM and IGT did not persist after repeat testing. The small number of new diabetics diagnosed from this screening study suggests that screening for diabetes in a predominantly European general practice is not cost effective in terms of the resources required.

Chromosomal assignment of a large tRNA gene cluster (tRNA(Leu), tRNA(Gln), tRNA(Lys), tRNA(Arg), tRNA(Gly)) to 17p13.1

A cluster of tRNA genes (tRNA(UAGLeu), tRNA(CUGGln), tRNA(UUULys), tRNA(UCUArg)) and an adjacent tRNA(GCCGly) have been assigned to human chromosome 17p12-p13.1 by in situ hybridization using a 4.2 kb human DNA fragment for tRNA(Leu), tRNA(Gln), tRNA(Lys), tRNA(Arg), and, for tRNA(Gly), 1.3 kb and 0.58 kb human DNA fragments containing these genes as probes. This localization was confirmed and refined to 17p13.100-p13.105 using a somatic cell hybrid mapping panel. Preliminary experiments with the biotinylated tRNA Leu, Gln, Lys, Arg probe and metaphase spreads from other great apes suggest the presence of a hybridization site on the long arm of gorilla (Gorilla gorilla) chromosome 19 and the short arm of orangutan (Pongo pygmaeus) chromosome 19 providing further support for homology between HSA17, GGO19 and PPY19.

The successful use of work oxen in agricultural development of tsetse infested land in Ethiopia

For the past five years a herd of work oxen, now numbering some 450 individuals, has been maintained under the protection of trypanocidal drugs on a settlement scheme in an area of western Ethiopia infested with tsetse. This paper describes the environmental conditions and the epizootiology of trypanosomiasis in the oxen and in the vector, Glossina morsitans. It is concluded that with the strategic use of drugs, oxen can be kept alive and perform useful agricultural work, in areas of high tsetse challenge, provided reasonable standards of veterinary supervision and management are maintained.