Biomedical subjects
Publications and source records attributed to S M Huson.
Three sibs, the offspring of first cousin Pakistani parents, are reported with an apparently 'new' form of spondyloepiphyseal dysplasia with microcephaly, unusual facies and moderate developmental delay.
Neurofibromatosis (NF) type 1 (NF1) is notable for its variable expression. To determine whether variation in expression has an inherited component, we examined 175 individuals in 48 NF families, including six MZ twin pairs. Three quantitative traits were scored--number of café-au-lait patches, number of cutaneous neurofibromas, and head circumference; and five binary traits were scored--the presence or absence of plexiform neurofibromas, optic gliomas, scoliosis, epilepsy, and referral for remedial education. For café-au-lait patches and neurofibromas, correlation was highest between MZ twins, less high between first-degree relatives, and lower still between more distant relatives. The high correlation between MZ twins suggests a strong genetic component in variation of expression, but the low correlation between distant relatives suggests that the type of mutation at the NF1 locus itself plays only a minor role. All of the five binary traits, with the exception of plexiform neurofibromas, also showed significant familial clustering. The familial effects for these traits were consistent with polygenic effects, but there were insufficient data to rule out other models, including a significant effect of different NF1 mutations. There was no evidence of any association between the different traits in affected individuals. We conclude that the phenotypic expression of NF1 is to a large extent determined by the genotype at other "modifying" loci and that these modifying genes are trait specific.
A panel of 200 unrelated NF1 individuals has been screened for mutations using a panel of specific clones for the entire gene. DNA analysis on conventional Southern blots indicated that (20) 10% of NF1 patients showed aberrant bands. Small lesions involving nucleotide alterations were detected in a further 10 patients; 5 of these alterations have been fully characterised and are the novel mutations in the NF1 gene. A number of mutations were identified in exon 2. Identical mutations in this exon in two unrelated individuals involved an insertion of cytosine into codon 5662 and resulted in an inappropriate stop codon. This mutation also created a new MnlI site. Another novel mutation in exon 2 resulted from the insertion of thymidine at nucleotide 5678, which also created an inappropriate stop codon. We have so far completed the screen of exons 1-9 of the NF1 gene for the identification of mutations and have found no evidence of clustering of such mutations in the gene.
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A clinical and genetic study of type 2 neurofibromatosis (NF2) has been carried out in the United Kingdom. Virtually complete ascertainment of cases in the north-west of England was achieved and suggests a population incidence of 1 in 33,000 to 40,000. In the UK as a whole, 150 cases have been identified and been used to study the clinical and genetic features of NF2. The autosomal dominant inheritance of NF2 was confirmed, 49% of cases were assessed as representing new mutations, and the mutation rate was estimated to be 6.5 x 10(-6). Evidence to support a maternal gene effect was found in that age at onset was 18.17 years in 36 maternally inherited cases and 24.5 in 20 paternally inherited cases (p = 0.027). The preponderance of maternally inherited cases was also significant (p = 0.03). Data are presented which suggest that there are two types of NF2, one with later onset and bilateral vestibular schwannomas as the only usual feature, and the other with earlier onset and multiple other tumours. A considerable number of cases did not fall easily into one or other group and other factors such as maternal effect on severity and anticipation need to be considered.
The major defining features, age at onset of symptoms, and survival in 150 patients with type 2 neurofibromatosis (NF2) have been studied. The mean age at onset was 21.57 years (n = 110) and no cases presented after 55 years of age. Patients presented with symptoms attributable to vestibular schwannomas (acoustic neuroma), cranial meningiomas, and spinal tumours. In 97 cases studied personally by the authors, skin and eye examination were found to be useful to detect early signs of the condition. Examination of the skin is likely to assist in early diagnosis in at least 10% of cases and examination of the eye for a lens opacity or cataract in at least as many again. There are marked interfamilial differences in disease severity and tumour susceptibility. Vestibular schwannomas are not fully penetrant, but the condition is usually expressed in another way. Alteration to the current diagnostic criteria is advocated to cover the lack of provision for new mutations. A screening protocol is proposed and the effect of disease heterogeneity on management is discussed.
A two year experience of DNA diagnosis for NF1 is presented. Twenty-three NF1 families have been analysed using 11 closely linked and intragenic markers. Prenatal testing was undertaken for six families; 11 affected subjects and their partners wished to know if they would be informative for future prenatal testing, seven of whom are so far fully informative. Presymptomatic testing was done for six subjects. Despite the availability of a series of closely linked markers, informativeness could not be achieved in all of the families tested.
A male infant, whose parents were first cousins, was born with tense chylous ascites, mild generalized oedema and facial dysmorphism. The baby initially seemed well but subsequently probably aspirated, developed septicaemia and finally died at 26 days from a bleeding diathesis, possibly secondary to liver dysfunction. No cause for the chylous ascites was found at post mortem. This case is presumed to represent an example of recessively determined chylous ascites. The mouse mutant Chy may be an homologous condition.
The clinical features, age at onset of symptoms and survival of 150 patients with type 2 neurofibromatosis were studied. The mean age at onset was 21.57 years (n = 110) and no patients presented after 55 years of age. Patients presented with symptoms attributable to vestibular schwannomas (acoustic neuroma), cranial meningiomas and spinal tumours. In 100 patients studied personally by the authors 44 per cent presented with deafness and this was unilateral in the majority (35/44). Deafness was accompanied by tinnitus in a further 10 per cent and muscle weakness or wasting was the first symptom in 12 per cent. Less common presenting symptoms were seizures (8 per cent), vertigo (8 per cent) numbness and tingling (2 per cent) and blindness (1 per cent). Eleven patients were diagnosed asymptomatically through screening. Café au lait spots occurred in 43 per cent (n = 43) but only one case had six. Skin tumours were detected in 68 per cent (68/100) and 38 per cent (34/90) had an identifiable lens opacity or cataract. The mean age at death in 40 cases was 36.25 years and all but one death was a result of a complication of neurofibromatosis. There are marked inter-family differences in disease severity and tumour susceptibility.
This paper describes three children of a Pakistani first cousin marriage with a distinctive, non-progressive disorder characterised by variable phalangeal anomalies, microcephaly, pre- and postnatal growth retardation, poor vision, dystonic movements, a characteristic face, and severe mental retardation. This combination of features seems to be distinct and to represent a new autosomal recessive syndrome.
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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.
Von Recklinghausen neurofibromatosis (NF-1) is a common autosomal dominant disorder. The estimated new mutation rate (1 x 10(-4] is one of the highest for a human disorder. Here we report that in 12 of 14 families we have analysed, the new mutation is of paternal origin. This result is similar to that recently obtained for retinoblastoma. In other genetic disorders that show a bias towards paternal origin of new mutations, there is a marked increase in the incidence of mutations with paternal age, consistent with the mutations arising from replication errors in mitosis of spermatogonial stem cells. In retinoblastoma and NF-1, however, such paternal age effects are slight or absent. The mechanism or timing of germline mutation could therefore be different in the two cases.
A family is described with type III syndactyly and facies resembling the oculodentodigital dysplasia facial phenotype in the absence of any of the other characteristic findings of the latter condition. The relationship between type III syndactyly and oculodentodigital dysplasia is discussed.
A case is reported where the major clinical features of craniostenosis and radial aplasia led to an initial diagnosis of Baller-Gerold syndrome. Mild fibular hypoplasia on skeletal survey led to review of the diagnosis and the similarity of the facial phenotype to that of Roberts syndrome was noted. Chromosome analysis showed the premature centromere separation characteristic of this condition. This case raises the question as to whether the Baller-Gerold syndrome can be considered as a distinct entity. It is suggested that cases diagnosed as having Baller-Gerold syndrome should have cytogenetic analysis and that known Roberts syndrome survivors are reviewed for signs of craniostenosis.
MASA syndrome (mental retardation, aphasia, shuffling gait and adducted thumbs) is an X-linked disorder first described in 1974. Since that time, two further pedigrees have been reported with similar features. The main clinical features are summarised by the acronym. Kenwrick et al. reported a separate family with X-linked recessive spastic paraplegia and mental retardation and demonstrated close linkage to DXS15 and DXS52 (DX13 and St14) at Xq28. Four affected individuals in this family were said to have absence of the extensor pollicis longus. Here we report a family where two adult brothers and their nephew have the phenotype of MASA syndrome. We demonstrate by clinical and gene mapping studies that MASA syndrome is most likely the same condition as that described by Kenwrick et al., and we review its clinical course and presentation.
Although one large family with hereditary motor and sensory neuropathy (HMSN) type I that showed linkage to the Duffy blood group (FY) on chromosome 1 has previously been reported, we have failed to find evidence for such linkage after examining 14 markers from chromosome 1 in 12 pedigrees. We have excluded linkage between HMSN I and FY up to theta = 0.15 (lod = -3.01) and also between HMSN I and markers flanking FY; amylase (AMY), polymorphic urinary mucin (PUM), serum amyloid protein (APCS), and alpha-spectrin (SPTA). We have excluded HMSN I from 70 cM around this linkage group. Other markers examined were MS1, oncogene L-myc (MYCL), beta-subunit of nerve growth factor (NGFB), oncogene N-ras (NRAS), glucocerebrosidase (GBA), apolipoprotein AII (APOA2), antithrombin III (AT3), renin (REN), and MS32. These cover both the long and the short arms of chromosome 1 in addition to the centromeric region and yielded no evidence of linkage to HMSN I. Two-point lod scores between these markers are also presented. It is possible that there are two or more loci for HMSN I and it will be necessary to obtain significant lod scores from individual families to resolve this issue. This is increasingly possible now that hypervariable genetic markers such as PUM are available.
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