Maternal 3;13 chromosome insertion, with severe pre-eclampsia.

A previously healthy young primigravida suffered very severe pre-eclampsia and was delivered at 32 weeks gestation. The baby was growth retarded with dysmorphic features, and died aged 4 days. Chromosome analysis of the baby revealed partial trisomy 13 resulting from recombination within a maternal insertion of part of 13q into 3p. To date, the maternal insertion has been identified in a further three members of the family and may have contributed to a number of spontaneous abortions, stillbirths and neonatal deaths in other family members. The various possibilities for recombination and malsegregation are discussed. An association between pre-eclampsia and trisomy 13 has been reported previously. To our knowledge this present paper constitutes the first report of partial trisomy for 13q occurring with pre-eclampsia.

Molecular studies of trisomy 18.

We have determined the parental origin of 50 cases of trisomy 18. In 48 cases the additional chromosome was maternal in origin, and in 2 cases it was paternal in origin. Seven cases, including both those with an additional paternal chromosome, appeared to be the result of postzygotic error. In contrast to the situation in nondisjunction involving chromosomes 21 and X, there was no evidence for nullochiasmate nondisjunction.

Long term effects of periconceptional multivitamin supplements for prevention of neural tube defects: a seven to 10 year follow up.

Periconceptional supplementation with Pregnavite Forte F was offered to women who presented consecutively to the Oxford genetic counselling service in the early 1980s who had previously had one or more pregnancies complicated by a neural tube defect. The first 100 children born alive to these women are the subject of this study. Birth weight, gestation, and congenital abnormalities were recorded. At age 2-5 years all 96 children remaining in the United Kingdom were assessed clinically and developmentally and behavioural information was obtained by questionnaire. At age 7-10 years, follow up of 91 children by telephone and postal questionnaire yielded further information about growth, general health, vision, hearing, and educational and behavioural status. Entry criteria excluded single mothers but the social class distribution of the sample was otherwise representative of the Oxfordshire population. There were no recurrences of neural tube defects. One child had radiological evidence of spina bifida occulta affecting only the fifth lumbar vertebra. One had an autosomal recessive disorder. Eight had random minor congenital anomalies. Birth weight for gestational age was significantly greater than for the local population and at age 7-10 years the girls were considerably taller than expected. Health, auditory, visual, and developmental status were no different from the general population. None of the children had special educational needs. None showed a major behaviour disorder but worries, fussiness, and fearfulness were highly significantly over represented.

Molecular studies of the fragile X syndrome.

We have studied families segregating for the fragile X syndrome for the presence of amplification of the CGG repeat sequence adjacent to the HpaII Tiny Fragment (HTF) island in the FMR-1 gene. We demonstrate that 138/143 fragile X positive, mentally retarded males show a characteristic smear of fragments corresponding to somatic variation in the amplification of the CGG sequence. In 7/8 normal transmitting males (NTM's), we show that there is a small amplification of sequence but no evidence for somatic variation. Defined mutated fragments in the size range found in NTM's are seen in daughters of NTM's. The daughters of these female carriers show either a defined fragment in the NTM size range, a defined larger fragment or a heterogeneous pattern of fragments. In the latter 2 cases the clinical phenotype of the females cannot easily be predicted, presumably because of variable X inactivation. In some families, the observed DNA genotype does not correlate with the phenotype; in others we demonstrate the occurrence of individuals with a mosaic DNA genotype. The implications of these data for diagnosis of the disease are discussed.

UK clinicians' knowledge of and attitudes to the prenatal diagnosis of single gene disorders.

Postal questionnaires were sent to 308 clinicians in the UK (general practitioners, obstetricians, clinical geneticists, neurologists, paediatricians, and paediatric neurologists) to assess their knowledge of, and attitudes to, the prenatal diagnosis of three common single gene disorders, Huntington's disease (HD), cystic fibrosis (CF), and Duchenne muscular dystrophy (DMD). Replies received numbered 213, a response rate of 69%. Overall, 95% of responding clinicians thought that offering prenatal diagnosis for the three test conditions was often or always appropriate. There was a correlation between the clinicians' estimates of life expectancy and their willingness to offer prenatal diagnosis (p less than 0.01). Among the non-geneticists questioned, fewer than 50% of general practitioners answered correctly regarding the availability of prenatal tests.

Interstitial deletion of the long arm of chromosome 18, del(18)(q12.2q21.1): a report of three cases of an autosomal deletion with a mild phenotype.

We describe three unrelated patients with apparently identical interstitial deletions of the segment (18) (q12.2q21.1). They were a short and markedly mentally retarded 5 year old girl, a macrocephalic and obese 2 1/2 year old boy with moderate mental retardation, and a macrocephalic, severely mentally retarded 5 year old boy. Findings common to all five liveborn patients so far identified as carrying this deletion include a pattern of minor dysmorphic features (prominent forehead, ptosis of the upper eyelids, full periorbital tissue, epicanthic folds, strabismus), muscular hypotonia, seizures, behavioural disorders, and lack of major malformations.

Severe limb abnormalities after chorion villus sampling at 56-66 days' gestation.

Among 289 pregnancies in which chorion villus sampling (CVS) was carried out at 56-66 days' gestation, 5 babies with severe limb abnormalities were subsequently identified. 4 had oromandibular-limb hypogenesis syndromes, and the other had a terminal transverse limb reduction defect. This high incidence raises the possibility that CVS was an aetiological factor for these developmental anomalies.

Ankyloblepharon filiforme adnatum in trisomy 18 Edwards syndrome.

Three cases of ankyloblepharon filiforme adnatum (AFA) in infants with Edwards syndrome are described. The case for a fifth subgroup of AFA is reinforced.

Investigation of three patients with the "ring syndrome", including familial transmission of ring 5, and estimation of reproductive risks.

We report three cases of ring chromosome 5 [r(5)], two familial (mother and daughter) and one sporadic. The phenotype resembled that of the "ring syndrome" with prenatal onset of short stature, growth retardation, mild facial dysmorphism and normal psychomotor development. Extended metaphase and prometaphase chromosome preparations using G-, R- and Q-banding and scanning electron microscopy (SEM) failed to demonstrate deletion in the ring 5. Flow karyotype using the FACS cell sorter and peak area analysis showed the r(5) to be in the same position as the normal chromosome 5. The deletion that is presumably associated with ring formation appears to involve less that one megabase of DNA. In the "complex" rings, high resolution SEM showed fragile sites at the 5q34 and 5q35 region with frequent deletions at that site. A literature survey suggests that when a parent carries a ring chromosome about 80% of recognised pregnancies result in live birth. Of these, about half have a normal phenotype and karyotype, and half inherit the parental ring; about half of those acquiring the ring (20%) show significant mental retardation.

Prevalence of Huntington's disease among UK immigrants from the Indian subcontinent.

Using the records of Churchill Hospital, Oxford, and those of genetics centres and other national institutions, the minimum prevalence of HD among immigrants from the Indian subcontinent was found to be almost half that found in the indigenous UK population. However, this observed prevalence was probably depressed, and therefore may not differ greatly from that estimated for European populations. All the identified cases were immigrants from Pakistan, the Punjab and Gujerat; none were from Bangladesh.

Neocerebellar hypoplasia in a neonate following intra-uterine exposure to anticonvulsants.

An infant with dysmorphic features was born to an epileptic mother who had taken phenytoin and sodium valproate throughout pregnancy. The infant began to have intractable seizures 10 minutes after delivery, and retrospective reports from the mother suggested they may have occurred in utero. Ultrasound examination of the brain showed a very wide subarachnoid space and CT confirmed cerebral and cerebellar underdevelopment. The infant died at three days of age and autopsy revealed a small brain with neocerebellar hypoplasia. This case might represent an extreme example of anticonvulsant teratogenicity.

Clinical features and molecular analysis of the alpha thalassemia/mental retardation syndromes. I. Cases due to deletions involving chromosome band 16p13.3.

We describe eight patients who have alpha thalassemia which cannot be accounted for by the Mendelian inheritance of abnormal alpha globin genes. Apart from the hematologic abnormality, the other universal clinical finding is mild to moderate mental handicap; there is also a broad spectrum of associated dysmorphic features. Initial analysis of the alpha globin gene complex (which maps to chromosome band 16p13.3), demonstrated that the alpha thalassemia results from failure of the patient to inherit an alpha globin allele from one of the parents. Using a combined molecular and cytogenetic approach, we have extended this analysis to show that all of these patients have 16p deletions which are variable in extent but limited to the terminal band 16p13.3; in at least four cases the deletion results from unbalanced chromosome translocation, and hence aneuploidy of a second chromosome is also present. The relatively nonspecific clinical phenotype contrasts with the other currently known microdeletion syndromes; this may reflect ascertainment bias in the recognition of such syndromes. This work represents the first step in the characterization of a new microdeletion syndrome that is probably underdiagnosed at present.

Clinical features and molecular analysis of the alpha thalassemia/mental retardation syndromes. II. Cases without detectable abnormality of the alpha globin complex.

We have identified five unrelated patients, all of north European origin, who have hemoglobin H (Hb H) disease and profound mental handicap. Surprisingly, detailed molecular analysis of the alpha globin complex is normal in these subjects. Clinically, they present with a rather uniform constellation of abnormalities, notably severe mental handicap, microcephaly, relative hypertelorism, unusual facies and genital anomalies. Hematologically, their Hb H disease has subtly but distinctly milder properties than the recognized Mendelian forms of the disease. These common features suggest that these five "nondeletion" patients have a similar underlying mutation, quite distinct from the 16p13.3 deletion associated with alpha thalassemia and mild to moderate mental retardation described in the accompanying paper. We speculate that the locus of this underlying mutation is not closely linked to the alpha globin complex and may encode a trans-acting factor involved in the normal regulation of alpha globin expression.

Oral fibromatosis in tuberous sclerosis.

Thirty-six families with tuberous sclerosis (TS) were clinically examined for oral fibromatosis and other previously reported oral anomalies. These consisted of 48 affected persons and 69 apparently unaffected parents and children. Fifty control subjects were also examined. Oral fibromatosis was observed in 56% of patients with typical TS and in none of 9 "atypical" cases. The total prevalence was 46%. Similar lesions were not seen in the control series, and they were rare in the otherwise apparently normal relatives with TS. However, three parents of patients with TS were found to have oral fibromas even though they had no signs of TS. It is suggested that examination for oral fibromatosis should be made in all persons suspected of having TS and in their close relatives, since such examination may identify other unsuspected carriers of the gene within the family.

Detection of breakpoints in submicroscopic chromosomal translocation, illustrating an important mechanism for genetic disease.

A 3-year-old boy presented with alpha-thalassaemia, dysmorphic features, and mental handicap. His younger sister is also mentally retarded, but haematologically normal. High resolution cytogenetic analysis revealed a normal karyotype in all family members. However, a combination of DNA analysis and in situ hybridisation demonstrated that the mother has a previously unsuspected balanced reciprocal translocation between the tips of the short arms of chromosomes 1 and 16, and that the alpha-globin gene complex (which maps to the tip of chromosome 16) is included in the translocated segment. Both of her children have inherited one of the translocation chromosomes in an unbalanced fashion: the boy has the derived chromosome 16, and therefore has alpha-thalassaemia, whilst the girl has the derived chromosome 1. Such cytogenetically invisible subtelomeric translocations are probably an important and hitherto unrecognised cause of genetic disease.

The nature of the defect in cobalamin G mutation.

Cobalamin G mutation (cblG) typically presents as a severe megaloblastic anemia during the first few weeks of life. The anemia responds completely to treatment with high doses of Cbl but the neurologic manifestations respond more slowly and not always completely. Cultured fibroblasts from two affected infants and virus-transformed lymphoblasts from one of the infants expressed the following: poor growth in the absence of methionine, the ability to take up and internalize Cbl bound to transcobalamin II, impaired synthesis of methionine from homocysteine, the ability to bind incoming Cbl to the respective coenzymes, but an inability to synthesize methylcobalamin in spite of a normal capacity to synthesize adenosylcobalamin. The in vitro activity of the methyltransferase dependent on methylcobalamin of cell extracts varied from low to high depending on the conditions of culture and assay. The cblG cells were unusually sensitive to the concentration of adenosylmethionine in the assay. More adenosylmethionine was required by cblG cells to achieve the same level of enzyme activity as control cells and high concentrations of adenosylmethionine did not suppress activity as in control cells. It was postulated that the defect in cblG is in the metabolism of adenosylmethionine, an essential substance for the synthesis of methionine from homocysteine.