Cost Effectiveness of Using Array-CGH for Diagnosing Learning Disability

OBJECTIVE

To undertake a cost-effectiveness analysis of using microarray comparative genomic hybridisation (array-CGH) as a first-line test versus as a second-line test for the diagnosis of causal chromosomal abnormalities in patients referred to a NHS clinical genetics service in the U.K. with idiopathic learning disability, developmental delay and/or congenital anomalies.

METHODS

A cost-effectiveness study was conducted. The perspective is that of a U.K. NHS clinical genetics service provider (with respect to both costs and outcomes). A cohort of patients (n = 1590) referred for array-CGH testing of undiagnosed learning disability and developmental delay by a single NHS regional clinical genetics service (South East Thames Regional Genetics Service), were split into a before-and-after design where 742 patients had array-CGH as a second-line test (before group-comparator intervention) and 848 patients had array-CGH as a first-line test (after group-evaluated intervention). The mean costs were calculated from the clinical genetics testing pathway constructed for each patient including the costs of genetic testing undertaken and clinical appointments scheduled. The outcome was the number of diagnoses each intervention produced so that a mean cost-per-diagnosis could be calculated. The cost effectiveness of the two interventions was calculated as an incremental cost-effectiveness ratio to produce an incremental cost-per-diagnosis (in 2013 GBP). Sensitivity analyses were conducted by altering both costs and effects to check the validity of the outcome.

RESULTS

The incremental mean cost of testing patients using the first-line testing strategy was -GBP241.56 (95% CIs -GBP256.93 to -GBP226.19) and the incremental mean gain in the percentage diagnoses was 0.39% (95% CIs -2.73 to 3.51%), which equates to an additional 1 diagnosis per 256 patients tested. This cost-effectiveness study comparing these two strategies estimates that array-CGH first-line testing dominates second-line testing because it was both less costly and as effective. The sensitivity analyses conducted (adjusting both costs and effects) supported the dominance of the first-line testing strategy (i.e. lower cost and as effective).

CONCLUSIONS

The first-line testing strategy was estimated to dominate the second-line testing strategy because it was both less costly and as effective. These findings are relevant to the wider UK NHS clinical genetics service, with two key strengths of this study being the appropriateness of the comparator interventions and the direct applicability of the patient cohort within this study and the wider UK patient population.

Impacts of introduced European hedgehogs on endemic skinks and weta in tussock grassland

Context Control of introduced pest species is based on the premise that there is a relationship between pest abundance and impact, but this relationship is rarely defined. Aim We investigated the impacts of introduced European hedgehogs (Erinaceus europaeus) on two species of small endemic skink (Oligosoma spp.) and flightless, nocturnal endemic orthopteran ground weta (Hemiandrus spp.), using an enclosure-based experimental manipulation of hedgehog density in tussock grasslands in the South Island of New Zealand. Methods We used capture–mark–recapture methods to estimate the densities of skinks before and after exposure to a range of hedgehog densities over a 3-month period and also compared changes in indices of abundance of skink demographic groups and ground weta. Key results Faecal analysis confirmed that hedgehogs consumed skinks and invertebrates in the enclosures. The proportional change between capture sessions in numbers of captured juvenile McCann’s skinks (O. maccanni) declined with increasing hedgehog density. Similarly, the proportional change in the numbers of ground weta encountered in pitfall traps showed a highly significant negative relationship with increasing hedgehog density. Total species abundances and numbers in other demographic skink groups did not change significantly in relation to hedgehog density. For overall skink abundance estimates, there was an apparent trend suggesting that changes in abundance were more negative with increasing hedgehog density, but this did not reach statistical significance for either skink species. Conclusions Our results confirmed that hedgehogs are important predators of small native fauna, but suggested that highly abundant prey populations may be buffered against significant impacts. Implications Less abundant prey and some demographic groups within populations, however, may be at significant risk from hedgehog predation.

Mutation detection rate and spectrum in familial hypercholesterolaemia patients in the UK pilot cascade project

Cascade testing using DNA-mutation information is now recommended in the UK for patients with familial hypercholesterolaemia (FH). We compared the detection rate and mutation spectrum in FH patients with a clinical diagnosis of definite (DFH) and possible (PFH) FH. Six hundred and thirty-five probands from six UK centres were tested for 18 low-density lipoprotein receptor gene (LDLR) mutations, APOB p.Arg3527Gln and PCSK9 p.Asp374Tyr using a commercial amplification refractory mutation system (ARMS) kit. Samples with no mutation detected were screened in all exons by single strand conformation polymorphism analysis (SSCP)/denaturing high performance liquid chromatography electrophoresis (dHPLC)/direct-sequencing, followed by multiplex ligation-dependent probe amplification (MLPA) to detect deletions and duplications in LDLR.The detection rate was significantly higher in the 190 DFH patients compared to the 394 PFH patients (56.3% and 28.4%, p > 0.00001). Fifty-one patients had inadequate information to determine PFH/DFH status, and in this group the detection rate was similar to the PFH group (25.5%, p = 0.63 vs PFH). Overall, 232 patients had detected mutations (107 different; 6.9% not previously reported). The ARMS kit detected 100 (44%) and the MLPA kit 11 (4.7%). Twenty-eight (12%) of the patients had the APOB p.Arg3527Gln and four (1.7%) had the PCSK9 p.Asp374Tyr mutation. Of the 296 relatives tested from 100 families, a mutation was identified in 56.1%. In 31 patients of Indian/Asian origin 10 mutations (two previously unreported) were identified. The utility of the ARMS kit was confirmed, but sequencing is still required in a comprehensive diagnostic service for FH. Even in subjects with a low clinical suspicion of FH, and in those of Indian origin, mutation testing has an acceptable detection rate.

Multiplex ligation-dependent probe amplification analysis to screen for deletions and duplications of the LDLR gene in patients with familial hypercholesterolaemia

The most common genetic defect in patients with autosomal dominant hypercholesterolaemia is a mutation of the low-density lipoprotein receptor (LDLR) gene. An estimate of the frequency of major rearrangements has been limited by the availability of an effective analytical method and testing of large cohorts. We present data from a cohort of 611 patients referred with suspected heterozygous familial hypercholesterolaemia (FH) from five UK lipid clinics, who were initially screened for point mutations in LDLR and the common APOB and PCSK9 mutations. The 377 cases in whom no mutation was found were then screened for large rearrangements by multiplex ligation-dependent probe amplification (MLPA) analysis. A rearrangement was identified in 19 patients. This represents 7.5% of the total detected mutations of the cohort. Of these, the majority of mutations (12/19) were deletions of more than one exon, two were duplications of more than one exon and five were single exon deletions that need interpreting with care. Five rearrangements (26%) are previously unreported. We conclude that MLPA analysis is a simple and rapid method for detecting large rearrangements and should be included in diagnostic genetic testing for FH.

Apert syndrome: the current role of prenatal ultrasound and genetic analysis in diagnosis and counselling

Apert syndrome is a rare congenital malformation syndrome characterized by the triad of cutaneous and progressive bony syndactyly, midfacial hypoplasia and craniosynostosis. Two missense mutations of the gene encoding the fibroblast growth factor receptor 2 (FGFR2) have been implicated in most cases. We report a case of Apert syndrome detected on prenatal ultrasound. Postnatal genetic analysis showed, for the first time, that the previously reported P253R mutation of the FGFR2 gene is also prevalent in southeast Europe. After prenatal sonographic detection of anomalies suggestive of Apert syndrome, parents should be counselled about prognosis and risk of recurrence, and the option of amniocentesis should be offered.

Multiplex ARMS analysis to detect 13 common mutations in familial hypercholesterolaemia

DNA analysis and mutation identification is useful for the diagnosis of familial hypercholesterolaemia (FH), particularly in the young and in other situations where clinical diagnosis may be difficult, and enables unambiguous identification of at-risk relatives. Mutation screening of the whole of the three FH-causing genes is costly and time consuming. We have tested the specificity and sensitivity of a recently developed multiplex amplification refractory mutation system assay of 11 low-density lipoprotein receptor gene (LDLR) mutations, one APOB (p.R3527Q) and one PCSK9 (p.D374Y) mutation in 400 patients attending 10 UK lipid clinics. The kit detected a mutation in 54 (14%) patients, and a complete screen of the LDLR gene using single-stranded conformation polymorphism/denaturing high performance liquid chromatography identified 59 different mutations (11 novel) in an additional 87 patients, for an overall detection rate of 35%. The kit correctly identified 38% of all detected mutations by the full screen, with no false-positive or false-negative results. In the patients with a clinical diagnosis of definite FH, the overall detection rate was higher (54/110 = 49%), with the kit detecting 52% of the full-screen mutations. Results can be obtained within a week of sample receipt, and the high detection rate and good specificity make this a useful initial DNA diagnostic test for UK patients.

DNA analysis: what and when to request?

Over the last 15 years genetic testing by DNA analysis has expanded enormously both in volume and range due to advances in scientific knowledge and analytical technology. This type of analysis has the potential to provide rapid, cost effective, and accurate diagnostic information but also has its limitations. Some of the changes detected may be of ambiguous consequence and as the knowledge base expands so too does the recognition that other factors can influence the clinical picture. In many cases outcomes may be predicted only on a statistical basis rather than individually. Careful attention should therefore be given to the clinical question that is being addressed before such testing is requested.

Immunological and genetic analysis of 65 patients with a clinical suspicion of X linked hyper-IgM

BACKGROUND

X linked hyper-IgM (XHIM) is a primary immunodeficiency caused by mutations in the tumour necrosis factor superfamily 5 gene, TNFSF5, also known as the CD40 ligand (CD40L) gene. Patients often present with recurrent infections, and confirmation of a diagnosis of XHIM enables appropriate therapeutic interventions, including replacement immunoglobulin, antibiotics, and bone marrow transplantation.

AIM

To review and optimise the institution's diagnostic strategy for XHIM.

METHOD

Samples from 65 boys were referred to this centre for further investigation of suspected XHIM. The results, which included a flow cytometric whole blood assay for CD40L expression followed by mutation analysis in selected patients, were reviewed.

RESULTS

Twenty one patients failed to express CD40L and TNFSF5 mutations were found in 20 of these patients. In contrast, no TNFSF5 mutations were found in 16 patients with weak expression of CD40L. Interestingly, one quarter of patients with confirmed XHIM who had TNFSF5 mutations had low concentrations of IgG, IgA, and IgM. Most of the remaining patients with XHIM had the classic pattern of normal or raised IgM with low concentrations of IgA and IgG.

CONCLUSIONS

This study demonstrates the usefulness of the whole blood staining method as a rapid screen to select patients for subsequent TNFSF5 mutation analysis, and shows the benefits of a unified protein/genetic diagnostic strategy.

Homozygous hypercholesterolaemia and ezetimibe: a case report

A girl of Indian origin presented with unusual nodules on her hands, and total cholesterol was found to be > 25 mmol/L. The girl had "mild" P664L mutation and total cholesterol levels fell by 38% when she was on a diet and statin therapy. A further reduction of 26% in total cholesterol and 37% in low-density lipoprotein (LDL) was achieved by adding ezetimibe to the treatment.

CONCLUSION

A case of homozygous hypercholesterolaemia is reported in order to highlight treatment options such as liver transplantation, LDL-aphaeresis and treatment with ezetimibe.

Genetic pathways of colorectal carcinogenesis rarely involve the PTEN and LKB1 genes outside the inherited hamartoma syndromes

Germline mutations of the PTEN/MMAC1/TEP and LKB1 genes cause hamartomas to develop in the gastrointestinal tracts of patients with Cowden syndrome and Peutz-Jeghers syndrome, respectively. PTEN mutations may also be responsible for some cases of juvenile polyposis. Histologically, hamartomas appear benign, but there is good evidence that in these syndromes, the hamartomas can progress to colorectal carcinoma. It remains unknown whether or not cancers that develop from hamartomas acquire a spectrum of mutations similar to those in sporadic colon cancers. PTEN and LKB1 are candidate genes for mutations in sporadic colon cancers, either as initiating events in tumorigenesis or providing a selective advantage during tumor growth. Using single-strand conformational polymorphism analysis, we have screened a set of sporadic colon cancers for somatic mutations in PTEN and LKB1. No variants predicted to alter protein function were detected in LKB1, but 1 of 72 cancers showed a somatic mutation in PTEN, together with allele loss. This cancer did not have a detectable APC mutation or allele loss at APC. It remains possible that PTEN and LKB1 are inactivated in other sporadic colon cancers by means such as deletion or promoter methylation. Like BRCA1 and BRCA2, however, it appears that PTEN and LKB1 mutations can cause cancers when present in the germline, but occur rarely in the soma.

Homozygotes and heterozygotes for ciliary neurotrophic factor null alleles do not show earlier onset of Huntington's disease

The CAG repeat number on Huntington's disease (HD) chromosomes accounts for about 60% of the variance in the age at onset of HD. However, distinct familial factors may also influence the age at onset. HD is associated with loss of medium-sized GABA-ergic striatal output neurons. Intracerebral administration of human ciliary neurotrophic factor (CNTF) protects striatal output neurons in excitotoxic rodent and primate models of HD induced by intrastriatal quinolinic acid injection. We have examined the effect of a common null mutation in the human CNTF gene on the age of onset of HD using a multiple regression approach that takes into account the CAG repeat number on HD chromosomes. We failed to detect an earlier onset of HD in nine homozygotes and 71 heterozygotes with this CNTF mutation compared with 203 homozygotes with wild-type alleles.

Genotypes at the GluR6 kainate receptor locus are associated with variation in the age of onset of Huntington disease

Huntington disease (HD) is associated with abnormal expansions of a CAG repeat close to the 5' end of the IT15 gene. We have assembled a set of 293 HD subjects whose ages of onset were known and sized their HD CAG repeats. These repeats accounted for 69% of the variance of age of onset when we used the most parsimonious model, which relates the logarithm of age of onset to a function of CAG repeat number. Since other familial factors have been proposed to influence the age of onset of HD, we have examined a number of candidate loci. The CAG repeat number on normal chromosomes, the delta2642 polymorphism in the HD gene, and apolipoprotein E genotypes did not affect the age of onset of HD. Although mitochondrial energy production defects in HD have led to suggestions that variants in the mitochondrial genome may be associated with clinical variability in HD, this suggestion was not supported by our preliminary experiments that examined the DdeI mitochondrial restriction fragment length polymorphism at position 10,394. Excitotoxicity has been a favored mechanism to explain the cell death in HD, particularly since intrastriatal injection of excitatory amino acids in animals creates HD-like pathology. Accordingly, we investigated the GluR6 kainate receptor. Of the variance in the age of onset of HD that was not accounted for by the CAG repeats, 13% could be attributed to GluR6 genotype variation. These data implicate GluR6-mediated excitotoxicity in the pathogenesis of HD and highlight the potential importance of this process in other polyglutamine repeat expansion diseases.

The Impact of Rabbit Control on Predator Sightings in the Semi-Arid High Country of the South Island, New Zealand

Extensive rabbit-poisoning operations were conducted under the Rabbit and Land Management Programme between 1990 and 1993 in the semi-arid high country of New Zealand. Repeated surveys of 371 km of spotlight transects that initially supported more than 40 rabbits per spotlight km showed a 95% decline in sighted rabbits. This was followed within a year by a 71% decline in sighted cats and ferrets. Wild cats and ferrets harbour bovine tuberculosis (Tb) and have an impact on protected native fauna. The means by which these apparent declines in predator numbers occur is important in assessing the role that rabbit control might play in managing for Tb and nature conservation.

Male neonatal death and progressive weakness and immune deficiency in females: an unknown X linked condition

We report a family with an undiagnosed X linked condition. The grandmother, two of her three daughters, and one of her grand-daughters have a slowly progressive proximal weakness, brisk reflexes, poor bladder function, static reduced night vision, and IgG2 deficiency. The diagnosis of the three living symptomatic females was "hereditary spastic paraplegia plus". They have lost five male children who died in the neonatal period of severe hypotonia and were of low birth weight. Investigations have not led to a unifying diagnosis: myotonic dystrophy, NARP, and X linked hyper IgM were specifically eliminated. Using the hypothesis that the condition is X linked dominant, haplotype analysis of the family suggests that the disease locus is within Xq26-qter. This entity should be considered in the differential diagnosis of families presenting with severe neonatal hypotonia in males and females with symptoms suggestive of complex hereditary spastic paraplegia.

Specific molecular prenatal diagnosis for the CTG mutation in myotonic dystrophy

The results of DNA analysis for the specific mutation of myotonic dystrophy are reported in eight pregnancies (two studied retrospectively) in six families. Four results were normal; in the other four, large DNA expansions were found, comparable to the range seen in severely affected children with congenital onset of the disorder. The results agreed with those obtained by linked DNA markers in the six cases where they were available. We conclude that specific molecular prenatal diagnosis of myotonic dystrophy is feasible, and that an abnormal result may also give a guide to possible severity, though this should be interpreted with caution until greater experience is available.

Forage biomass and kangaroo populations (Marsupialia: Macropodidae) in summer and autumn at Hattah-Kulkyne National Park, Victoria

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