Ann Curtis

Neuroferritinopathy in a French family with late onset dominant dystonia

We recently described a dominantly inherited movement disorder in a large family from Cumbria in the north west of England resulting from an adenine insertion at position 460–461 in the ferritin light polypeptide gene (FTL).1 The disease presented between the ages of 38 and 58 years with chorea in some subjects, focal dystonia in other subjects, and an akinetic rigid parkinsonian syndrome in others. Brain imaging showed basal ganglia cavitation that was confirmed at necropsy. Neuronal loss was accompanied by the formation of neuroaxonal spheroids, with intraneural and extraneural iron deposition. Serum ferritin levels were low in the presence of normal serum iron, transferrin and haemoglobin levels. The results of these investigations provided a direct link between a primary disorder of iron storage metabolism and a late onset neurodegenerative movement disorder.1 Cumbria has a stable, largely white population of Anglo-Saxon and Norman origins. All of the affected subjects described in the original report lived within a 30 mile radius and were traced, using parish records, back to a probable common founder born around 1790.1 A further 10 familial cases with the same mutation were found by screening over 100 patients from northern England with undiagnosed extrapyramidal disease and a small number of other cases referred to us from other parts of the country. The nature of the mutation and our report here of a common haplotype around the gene suggested to us that neuroferritinopathy would be a rare disorder in the UK, likely to have been inherited from a single founder. However, a careful review of published reports identified a number of potentially similar families outside the United Kingdom, including one family from the north of France.

Use of linkage disequilibrium data in prenatal diagnosis of cystic fibrosis.

SummaryParents at risk of bearing a child with cystic fibrosis, and who have no living affected child, often use prenatal diagnosis based on microvillar enzyme assay in second-trimester amniotic fluid samples. If enzyme levels are abnormal and the pregnancy is terminated, it is possible in principle to use the fetal tissues to establish the phase relationship of linked DNA markers for a subsequent first-trimester prenatal diagnosis. However, the probability of a fetus being affected after an abnormal microvillar enzyme test may be no greater than 80%. The strong linkage disequilibrium between haplotypes at the D7S23 locus and the cystic fibrosis gene may be used to increase this probability. If fetal tissues are homozygous for the 6.6-kb band defined by pKM.19 and PstI and also homozygous for the 2.1-kb band with pXV-2c and TaqI, the chance of being affected increases from 80% to between 95% and 97%. We regard this as being sufficiently certain for use in phase determination.

Prenatal exclusion testing for Huntington's disease: a problem of too much information.

At eight weeks of pregnancy a couple were informed that the prospective fathers mother had died of Huntingtons disease (HD). There were no living affected members in the immediate family to confirm the diagnosis. By inspection of the local genetic register, it was established that it was indeed HD segregating in the extended family. Genotyping of the prospective mother and father, the fathers unaffected father, and his unaffected maternal grandmother was carried out using a battery of polymorphic DNA markers, including a new probe which has a very low recombination rate with the HD locus. Analysis of DNA from a chorionic villus sample taken at 10 weeks of pregnancy showed that the fetus must have inherited a chromosome from its fathers affected mother. Its risk of developing HD was 47%. If the genotype of the unaffected maternal grandmother was taken into account, the risk was reduced to 42%. Neither risk was considered acceptable by the prospective parents and the pregnancy was terminated at 12 weeks gestation. Prospects for future pregnancies are good, with a 50% chance of having a child whose risk of inheriting the HD gene is less than 1.5%. In retrospect it was noted that although genotyping of the maternal grandmother had refined the fetal risk, it had also nearly contributed to an inadvertent and unwanted predictive test for HD on the father. This case makes the point that in prenatal exclusion testing, linkage information must be generated with considerable care.

MLH1 Differential allelic expression in mutation carriers and controls.

Germline defects in the MLH1 gene are associated with Lynch syndrome. A substantial proportion of these mutations leads to premature termination codons and can induce nonsense mediated decay (NMD) of the corresponding transcript. Resulting allelic expression differences represent a fast and inexpensive method to identify patients carrying MLH1 mutations. In patients and controls, we show that allelic expression imbalance (AEI) can be readily detected in RNA extracted from whole blood from patients carrying mutations expected to elicit NMD using mass spectrometry. Mutations closer to the 5′ end of the gene tend to show smaller imbalances. AEI can also be detected in normal controls. Analysis of allelic expression in controls and individuals with mutations not expected to exhibit NMD revealed that MLH1 expression is influenced by sequence variation acting in cis. A maximum likelihood framework was used to identify two SNPs, rs1799977 (c.655G>A; p.I219V) and rs1800734 (c.‐93 G>A) that are independently associated with expression. These influences are, however, small compared to the differences associated with pathological variants.

Confirmation of prenatal diagnosis of cystic fibrosis by DNA typing of fetal tissues.

Tissues from eight fetuses, diagnosed on the basis of amniotic fluid microvillar enzyme assay as having cystic fibrosis, were conserved in frozen storage for up to three years. Adequate samples of undegraded DNA could be extracted from small intestine, lung, and liver. DNA typing, with restriction fragment length polymorphisms tightly linked to the cystic fibrosis gene, showed all eight diagnoses to have been correct. Determining the DNA genotype of fetal material can also be used to establish the linkage relationship between markers and the cystic fibrosis gene, and will permit subsequent first trimester prenatal diagnosis for couples who have no living affected child.

Genotyping of cystic fibrosis families with linked DNA probes

Forty‐six British families, containing at least one child affected with cystic fibrosis, were typed for restriction fragment length polymorphisms (RFLPs) by the probes pmet H, pmet D, pJ3.11 and 7c22. Thirty‐five (76%) were fully informative for prenatal diagnosis and carrier detection, while in the remainder prenatal exclusion of an affected fetus could be carried out in half the pregnancies. The frequencies of individual alleles did not differ between cystic fibrosis and normal chromosomes. However, the previously noted excess of one haplotype on chromosomes carrying the cystic fibrosis gene was confirmed.

The haplotype distribution of the delta F508 mutation in cystic fibrosis families in Scotland.

SummaryThe gene defective in cystic fibrosis (CF) has recently been isolated and the major mutation identified. The haplotype distribution of this mutation (ΔF508) has been determined for 215 CF chromosomes in the Scottish population. ΔF508 represents 73% of all CF mutations in this group. There remains considerable linkage disequilibrium between XV2c and KM19 and other mutations in the CF gene.

Presymptomatic testing for Huntington's disease

SummaryPresymptomatic testing for Huntingtons disease (HD) is possible through the use of restriction fragment length polymorphisms (RFLPs) at the closely linked D4S10 locus. Recombination between the HD and D4S10 loci will occur in 4%–5% of meioses, and is a well-recognised complication of predictive testing. Recombination between RFLPs within the D4S10 locus is a rare event and can usually be ignored. We report a case where such an intra-locus recombination frustrated attempts to predict the chance of a high-risk individual inheriting the HD gene.

Genetic linkage between Huntington's disease and D4S10(G8) in Scottish families

Genetic linkage between Huntingtons disease (HD) and polymorphic DNA markers at the D4S10 locus has been investigated in 16 Scottish families. A maximum lod score of 3.499 at a recombination fraction of 0.07 was found, with 95% confidence limits of 0.02 and 0.22. Only one obvious recombinant was detected, and the wide confidence limits probably reflect the large number of unaffected individuals whose risk could only be estimated empirically.

Predictive testing for Huntington's disease with linked DNA markers

Gynecologic Oncology Service, Walter Reed Army Medical Center, Washington, DC20307-5001; USA Gynecologic Oncology; 34/2 (219-221)/1989/ Lymph node metastasis is uncommon in patients with microinvasive squamous cel1 carcinoma of the cervix and is particularly unusal in tumors with early stromal invasion. We describe a patient with maximum stromal invasion of 0.8 mm who had extensive pelvic and para-aortic nodal metastases discovered at laparotomy. Despite combined modality therapy, she died with progressive disease. New clinical staging definitions for Stage IA cervical carcinoma incorporate measurement of both depth of invasion and lateral tumor spread and have resolved many of the descriptive controversies surrounding this entity. Our case illustrates that any degree of stromal invasion carries some risk of nodal metastasis. The management of patients with microinvasive carcinoma should be individualùed. An abdominal approach should be considered for patients being treated by extrafascial hysterectomy to allow assessment of the regional lymph nodes. Whether more aggressive therapy wil1 influence the outcome for the rare patient with lymph node metastasis is unknown.