Susan Holloway

A Chromosomal Duplication Map of Malformations: Regions of Suspected Haplo- and Triplolethality—and Tolerance of Segmental Aneuploidy—in Humans

The distribution of simple autosomal duplications associated with congenital malformations has been analyzed by means of data contained in the Human Cytogenetics Database. For each of the 47 malformations, the frequency of duplication of a given chromosome band associated with the malformation was compared with the overall frequency of duplication of that band recorded in the database. In total, there were 143 malformation-associated chromosomal regions (MACR); 21 of these contained at least one band with a highly significant (P<.001) association. The average number of bands per MACR was 3.1. Eight bands, representing 2.1% of haploid autosomal length, were not involved in any duplication, and we suggest that these are potentially triplolethal. This compares with 31 bands, representing 11% of haploid autosomal length, that were identified in the previously reported deletion map and that were not involved in any deletion and are potentially haplolethal. In both cases, approximately half of these bands are pericentromeric. The longest duplication involves 4.3% of haploid autosomal length, and the longest deletion involves 2.7%.

The prognosis of adult-onset motor neuron disease: a prospective study based on the Scottish Motor Neuron Disease Register

The Scottish Motor Neuron Disease Register (SMNDR) is a prospective, collaborative, population-based project which has been collecting data on incident patients since 1989. In this report we present the clinical features of 229 patients with motor neuron disease (218 sporadic and 11 familial) diagnosed in 1989 and 1990 and compare their prognosis with previous studies of survival. The overall 50% survival from symptom onset was 2.5 years (95% CI, 2.2–3.0) and 5-year survival 28% (95% Cl, 20–36%). The presence of progressive bulbar palsy (PBP), either at presentation or developing during the course of the illness, significantly reduced survival and was the most important prognostic indicator. Patients who survived longer than 5 years from symptom onset did not have BP as part of their presenting illness. The prognosis was worse for women, and this was in part related to the higher frequency of PBP in older women, but age was also an independent adverse risk factor. Differences in survival between this and previous series can probably be explained on the basis of variation in case definition and ascertainment methods.

A Locus for Isolated Cleft Palate, Located on Human Chromosome 2q32

We present evidence for the existence of a novel chromosome 2q32 locus involved in the pathogenesis of isolated cleft palate. We have studied two unrelated patients with strikingly similar clinical features, in whom there are apparently balanced, de novo cytogenetic rearrangements involving the same region of chromosome 2q. Both children have cleft palate, facial dysmorphism, and mild learning disability. Their karyotypes were originally reported as 46, XX, t(2;7)(q33;p21) and 46, XX, t(2;11)(q33;p14). However, our molecular cytogenetic analyses localize both translocation breakpoints to a small region between markers D2S311 and D2S116. This suggests that the true location of these breakpoints is 2q32 rather than 2q33. To obtain independent support for the existence of a cleft-palate locus in 2q32, we performed a detailed statistical analysis for all cases in the human cytogenetics database of nonmosaic, single, contiguous autosomal deletions associated with orofacial clefting. This revealed 2q32 to be one of only three chromosomal regions in which haploinsufficiency is significantly associated with isolated cleft palate. In combination, our data provide strong evidence for the location at 2q32 of a gene that is critical to the development of the secondary palate. The close proximity of these two translocation breakpoints should also allow rapid progress toward the positional cloning of this cleft-palate gene.

Further evidence of the increased risk for malignant peripheral nerve sheath tumour from a Scottish cohort of patients with neurofibromatosis type 1

A recent study, looking at the lifetime risk of developing malignant peripheral nerve sheath tumour (MPNST) in patients with neurofibromatosis type 1 (NF1), estimated the risk to be 8–13%. Prior to this, longitudinal studies had shown that patients with NF1 had a risk of 4–5% of developing MPNST, and cross-sectional studies had found that only 1–2% of patients with NF1 had MPNST. The aim of this study was to estimate the lifetime risk of MPNST in patients with NF1 in southern Scotland, using patient records obtained from the Edinburgh and Glasgow Genetic Units and Scottish Cancer Register. In the period 1993–2002, 14 patients with NF1 were diagnosed with MPNST in a population of 3.5 million. The lifetime risk of MPNST in the Scottish patients with NF1 was calculated to be 5.9–10.3%. This provides further evidence that patients with NF1 are at greater risk of developing MPNST than was previously estimated, and emphasises the importance of educating patients about suspicious symptoms, which may need an urgent medical opinion. The mean age at diagnosis of MPNST (p<0.05) and 5-year survival (p<0.01) were significantly lower in patients with NF1 than in unaffected individuals. This may be due to patients with NF1 presenting later, because the tumour is mistaken for a neurofibroma, or due to MPNST having a more aggressive course in NF1.

A study of the Huntington's disease associated trinucleotide repeat in the Scottish population.

Accurate measurements of a specific CAG repeat sequence in the Huntingtons disease (HD) gene in 337 HD patients and 229 normal controls from the Scottish population showed a range from 35 to 62 repeats in affected subjects and eight to 33 in normal subjects. A link between early onset of symptoms and very high repeat number was seen. For HD patients with the most common affected allele sizes (39 to 42 repeats) absolute repeat size was a poor index for the age at onset of symptoms. There was variability in the transmitted repeat size for both sexes in the HD size range. We observed a significant increase of repeat size for paternal transmission of the disease and greater instability for paternally transmitted CAG repeats in the HD size range.

Patient satisfaction with two different models of cancer genetic services in south-east Scotland

There is a need to integrate primary- and secondary-care cancer genetic services, but the most appropriate model of service delivery remains unclear. This study reports patients’ expectations of breast cancer genetic services and a comparison of their satisfaction with two service models. In the first model, risk assessment was carried out using mailed family history data. Women estimated as being at high/moderate risk were offered an appointment at the familial breast cancer clinic, and those at low risk were sent a letter of reassurance. In the second model, all women were seen by a genetic nurse specialist, who assessed risk, referred high/moderate-risk women to the above clinic and discharged those at low risk. Over 60% of all women in the study regarded access to breast screening by mammogram and regular check-ups as very important. This underlines the demand for a multidisciplinary service providing both clinical genetic and surgical services. Satisfaction was high with both models of service, although significantly lower among women not at increased cancer risk and thus not offered a clinical check-up and mammography. Increased cancer worry was associated with a greater expressed need for information and for reassurance through follow-up clinical checks and mammography. Better targeting of counselling to the expressed concerns and needs of these women is required to improve the service offered. GPs and patients expressed no clear preference for any specific service location or staffing configuration. The novel community service was less expensive in terms of both staff and patient costs. The potential to decrease health staff/patient contact time and to employ nurse practitioners with both clinical genetic and oncology training should be explored further. The rapidly rising demand for these services suggests that the evaluation of further new models needs to continue to be given priority to guide the development of cancer genetic services.

FISH Mapping of De Novo Apparently Balanced Chromosome Rearrangements Identifies Characteristics Associated with Phenotypic Abnormality

We report fluorescence in situ hybridization (FISH) mapping of 152, mostly de novo, apparently balanced chromosomal rearrangement (ABCR) breakpoints in 76 individuals, 30 of whom had no obvious phenotypic abnormality (control group) and 46 of whom had an associated disease (case group). The aim of this study was to identify breakpoint characteristics that could discriminate between these groups and which might be of predictive value in de novo ABCR (DN-ABCR) cases detected antenatally. We found no difference in the proportion of breakpoints that interrupted a gene, although in three cases, direct interruption or deletion of known autosomal-dominant or X-linked recessive Mendelian disease genes was diagnostic. The only significant predictor of phenotypic abnormality in the group as a whole was the localization of one or both breakpoints to an R-positive (G-negative) band with estimated predictive values of 0.69 (95% CL 0.54-0.81) and 0.90 (95% CL 0.60-0.98), respectively. R-positive bands are known to contain more genes and have a higher guanine-cytosine (GC) content than do G-positive (R-negative) bands; however, whether a gene was interrupted by the breakpoint or the GC content in the 200 kB around the breakpoint had no discriminant ability. Our results suggest that the large-scale genomic context of the breakpoint has prognostic utility and that the pathological mechanism of mapping to an R-band cannot be accounted for by direct gene inactivation.

International collaborative study of the spinal muscular atrophies. Part 1. Analysis of clinical and laboratory data.

There is considerable variation in age of onset, though in over three-quarters of cases onset is before 4 years of age. A febrile episode, often of viral origin, may be present at the time of onset and might possibly be of aetiological significance, perhaps by precipitating the disease in a genetically predisposed individual. Reduced fetal movements and floopiness at birth are present in about one third of those cases where the onset is in early childhood. It would seem that when the onset is before 4 years of age, and particularly if the child has never been able to sit without support, the prognosis is much worse than in cases where the onset is after the age of 4 years. The proximal limb muscles are predominantly affected and muscle tone is usually reduced but pseudohypertrophy is uncommon. Rarely are the cranial nerves affected. Muscle fasiculations are present in about half the cases. Almost 10% of cases appear to be mentally retarded. With regard to the EMG findings, spontaneous activity, reduced full effort pattern increased potential amplitude and duration and increased motor unit territory appear to be the most reliable diagnostic criteria. Routine histological evidence of neurogenic atrophy seems to be a more reliable diagnostic criterion than muscle histochemistry. However, this may be only reflect the way in which the data were selected, that is, from cases where a muscle biopsy showed evidence of neurogenic atrophy on routine histology. Finally the serum level of creatine kinase is rarely very high and in more than half the cases it is normal. The CSF chemistry is always normal.

Life expectancy and death from cardiomyopathy amongst carriers of Duchenne and Becker muscular dystrophy in Scotland

Objectives: To assess life expectancy and cardiovascular mortality in carriers of Duchenne and Becker muscular dystrophy. Design: Family pedigrees of individuals affected with these conditions, held by the four genetics centres in Scotland, were examined to identify a cohort of definite carriers. Electronic death registration data, held by the General Register Office for Scotland, were used to identify death certificates of carriers who had died, to obtain age at death and cause of death. Survival and mortality data were obtained for the general population for comparison. Patients: 397 definite carriers in 202 pedigrees were identified from which 94 deaths were identified by record linkage to death certificates. Main outcome measures: Observed numbers surviving to certain ages and numbers dying of cardiac causes were compared with expected numbers calculated from general population data. Results: There were no significant differences between observed and expected numbers surviving to ages 40–90. The standardised mortality ratio for the 371 carriers alive in 1974 was 0.53 (95% confidence interval 0.32 to 0.82). Conclusions: Whereas female carriers may have clinical features of cardiomyopathy, this study does not suggest that this is associated with reduced life expectancy or increased risk of cardiac death. Routine cardiac surveillance of obligate carriers is therefore probably unnecessary.

Referrals of women with a family history of breast cancer from primary care to cancer genetics services in South East Scotland

As part of a cluster randomised trial to assess an alternative model of cancer genetics services, we gathered data on all referrals from general practitioners (GPs) to cancer genetics services in South East Scotland over a 4-year period. The referral rate per 1000 patients rose by 48% from 0.21 in the 2-year period before the trial to 0.31 during the trial. This increase was much greater in the trial group offered the GP clinic service (64% increase compared to a 38% increase in those referred to the regional service). Thus, the offer of a more local service appeared to have a marked effect on GP management of these women. Referral rates to cancer genetics services from general practices varied widely with higher referral rates from practices with more female partners. There was a negative correlation between referral rates and practice area deprivation scores. However, this was not found during the trial in the group which offered clinics in general practice, the provision of clinic appointments nearer to the homes of more socially deprived women resulting in improved access to women from deprived areas. The interaction with the GP appears to be associated with an inappropriate level of interest in and expectation of the appropriateness of genetic testing. The provision of the clinics within general practice did not result in higher levels of confidence among GPs in managing these women.