Timing of morphological and ecological innovations in the cyanobacteria--a key to understanding the rise in atmospheric oxygen.

When cyanobacteria originated and diversified, and what their ancient traits were, remain critical unresolved problems. Here, we used a phylogenomic approach to construct a well-resolved 'core' cyanobacterial tree. The branching positions of four lineages (Thermosynechococcus elongatus, Synechococcus elongatus, Synechococcus PCC 7335 and Acaryochloris marina) were problematic, probably due to long branch attraction artifacts. A consensus genomic tree was used to study trait evolution using ancestral state reconstruction (ASR). The early cyanobacteria were probably unicellular, freshwater, had small cell diameters, and lacked the traits to form thick microbial mats. Relaxed molecular clock analyses suggested that early cyanobacterial lineages were restricted to freshwater ecosystems until at least 2.4 Ga, before diversifying into coastal brackish and marine environments. The resultant increases in niche space and nutrient availability, and consequent sedimentation of organic carbon into the deep oceans, would have generated large pulses of oxygen into the biosphere, possibly explaining why oxygen rose so rapidly. Rapid atmospheric oxidation could have destroyed the methane-driven greenhouse with simultaneous drawdown in pCO(2), precipitating 'Snowball Earth' conditions. The traits associated with the formation of thick, laminated microbial mats (large cell diameters, filamentous growth, sheaths, motility and nitrogen fixation) were not seen until after diversification of the LPP, SPM and PNT clades, after 2.32 Ga. The appearance of these traits overlaps with a global carbon isotopic excursion between 2.2 and 2.1 Ga. Thus, a massive re-ordering of biogeochemical cycles caused by the appearance of complex laminated microbial communities in marine environments may have caused this excursion. Finally, we show that ASR may provide an explanation for why cyanobacterial microfossils have not been observed until after 2.0 Ga, and make suggestions for how future paleobiological searches for early cyanobacteria might proceed. In summary, key evolutionary events in the microbial world may have triggered some of the key geologic upheavals on the Paleoproterozoic Earth.

Genetics in methanogens: transposon insertion mutagenesis of a Methanococcus maripaludis nifH gene.

We designed a transposon insertion mutagenesis system for Methanococcus species and used it to make mutations in and around a nifH gene in Methanococcus maripaludis. The transposon Mudpur was constructed with a gene for puromycin resistance that is expressed and selectable in Methanococcus species. A 15.6-kb nifH region from M. maripaludis cloned in a lambda vector was used as a target for mutagenesis. A series of 19 independent Mudpur insertions spanning the cloned region were produced. Four mutagenized clones in and around nifH were introduced by transformation into M. maripaludis, where each was found to replace wild-type genomic DNA with the corresponding transposon-mutagenized DNA. Wild-type M. maripaludis and a transformant containing a Mudpur insertion upstream of nifH grew on N2 as a nitrogen source. Two transformants with insertions in nifH and one transformant with an insertion downstream of nifH did not grow on N2. The transposon insertion-gene replacement technique should be generally applicable in the methanococci for studying the effects of genetic manipulations in vivo.

The ocular pathology of Norrie disease in a fetus of 11 weeks' gestational age.

The ocular pathology of Norrie disease was studied for the first time in a fetus of 11 weeks' gestation, following prenatal diagnosis using genetic markers for Norrie disease and elective abortion. The eyes were histologically normal, with no evidence of primary neuroectodermal maldevelopment of the retina, previously postulated to be the cause of the ocular changes. We believe that the retinal and other manifestations of Norrie disease are the result of a primary abnormality of vascular proliferation, probably in relation to persistent hyperplastic primary vitreous after approximately 14 weeks' gestation. We postulate that the ocular and otological effects of Norrie disease may be due to a genetically mediated abnormality of secretion of, or sensitivity to, angiogenic growth factors at endodermal-neuroectodermal interfaces during fetal and postnatal development.

Early onset hereditary spinocerebellar ataxia: an autosomal recessive disorder distinct from Friedreich's ataxia.

The important clinical features of seven patients with an early onset slowly progressive heredofamilial spinocerebellar degenerative disorder of probably autosomal recessive inheritance included limb ataxia, retained and/or exaggerated tendon reflexes (biceps and knee), pyramidal weakness of lower limbs and normal sensory action potentials. This rare disorder is probably distinct from Friedreich's ataxia and carries a better prognosis.

Carrier detection and prenatal diagnosis in Norrie disease.

We report the use of DNA probes to determine carrier status in three young women from a large kindred with Norrie disease. One of the women requested prenatal diagnosis during pregnancy. In this pedigree, Norrie disease was not characterized by a deletion at DXS7.

An evaluation of reinforcement of genetic counselling on the consultand.

This project studied the effect of reinforcement of genetic counselling in the home, on consultand recall of information discussed in the clinic. Acceptable recall was observed in 84% of 227 patients scored for recall of rate of recurrence, understanding of the nature of the disease at special risk and of its mechanism of origin. Our results show no significant difference in the frequency of acceptable recall after reinforcement of genetic counselling compared with an absence of reinforcement. The consultands' understanding was substantially affected by the type of genetic mechanism involved.

Clinical manifestations of trisomy 5q.

A patient with a small deletion of the short arm and a partial duplication of the long arm of chromosome 5 is described. The main clinical features include craniofacial dysmorphism, growth failure, developmental retardation, and congenital heart defect. The mother and male sib each carried an inv(5) (p15.3q35) but were phenotypically normal. The possible clinical manifestations of partial duplication of the long arm of chromosome 5 are discussed with a review of previous published reports.

Screening for polycystic kidney disease: importance of clinical presentation in the newborn.

Fifty per cent of the offspring of adults with the adult (dominant) form of polycystic kidney disease are carriers of the abnormal gene. Clinical symptoms and signs before adolescence are rare, but renal ultrasonography may detect evidence of cyst formation. Twenty two children, all offspring of parents with known adult polycystic kidney disease, have undergone renal ultrasonography. In six cases evidence of disease was detected without clinical manifestations at the ages of 1, 2, 5, 8, 13, and 14 years. There were no renal masses, hypertension, haematuria, or evidence of renal insufficiency. In four children from three sibships, whose families had no previous history of renal disease, bilateral renal masses were noted to be present at birth. In each case one parent was subsequently found to have adult polycystic kidney disease. At the ages of 1, 4, 6, and 20 years, while renal masses were still palpable, there was no evidence of renal insufficiency or hypertension in the younger children, while the oldest had mild renal failure. An analysis of the reported cases in childhood is suggestive of a bimodal distribution of enlarged kidneys, with a number of cases diagnosed at birth or soon after, followed by an increasing incidence during later childhood. Adult polycystic kidney disease presenting at birth may be qualitatively different from the disease detected by screening programmes of children at risk.

A family with craniofrontonasal dysplasia, and fragile site 12q13 segregating independently.

Coronal craniosynostosis, hypertelorism, telecanthus, broad grooved nasal tip, dental anomalies, mild syndactyly and broad thumbs, consistent with craniofrontonasal dysplasia are described in a family of four affected females over three generations. Documentation of the family is of interest because of variable clinical features and an excess of affected females. The excess of females observed in this condition is as yet unexplained, but cannot be referred simply to X-linked dominance with lethality in the male. Autosomal dominance with less frequent and less severe expression in the male is more tenable. Chromosome analysis on two affected family members revealed a fragile site at 12q13, which was also found in a phenotypically normal family member. A third affected individual did not exhibit this fragile site. Thus it appears that there is a heritable fragile 12q13 site segregating in this family separately from the gene for craniofrontonasal dysplasia.

Hereditary cerebellar ataxia and genetic linkage with HLA.

Five families with at least three generations of members affected with autosomal dominant spinocerebellar ataxia (SCA) were studied. HLA typing was carried out and the coded HLA haplotypes were used to calculate the likelihood of linkage using the LIPED computer program. The combined lod scores from these five families does not, by itself, support linkage. Negative lod scores were observed in all five families, however, when pooled with the previously published data significant lod scores were obtained [Z = 3.343 (theta = 0.20) and +4.286 (theta = 0.30)]. In four families, affected members had clinical features consistent with autosomal dominant cerebellar ataxia (ADCA) type I while in the fifth, ADCA type II was suggested. Clinical heterogeneity within ADCA raises doubts about the significance of summed lod scores. In view of the previous reports probably two genetically heterogeneous types of ADCA exist -- HLA linked and nonlinked.

Cornelia de Lange syndrome in several members of the same family.

A family is reported in which several members have the Cornelia de Lange syndrome and other members show facial dysmorphism and other features reminiscent of this syndrome. The segregation pattern is consistent with the view that the dysmorphic features (variable) are the manifestation of a single gene in heterozygous form. Chromosome abnormality was not found.

Interstitial deletion of the short arm of chromosome 5 in a mother and three children.

An interstitial deletion (5) (p13p15.1) was found in a mentally retarded woman and three of her four children. The variable manifestation of this chromosomal defect and the relevance of this particular deletion to the cri du chat syndrome are discussed. To our knowledge the only other reported case of inherited 5p deletion from an affected parent involved the terminal segment of the 5p15.3 band.

Absorption and circular dichroism studies of a gold (I)-DNA complex.

The DNA binding properties of the Au(I)-containing antiarthritic drug Ridaura and related Au(I) complexes have been investigated. Absorption and circular dichroism spectroscopy show that if the gold ion possesses an easily displaced ligand, e.g., Cl- or Br-, Au(I) is capable of interacting, in a nondenaturing fashion, with calf thymus DNA. Absorption studies with the four DNA nucleosides suggest that guanine and cytosine bases are important in the Au(I)DNA interaction.

Grebe chondrodysplasia and brachydactyly in a family.

A family is reported in which various skeletal abnormalities have been segregating over three generations. The Great-grandfather (11) of the consultand had features consistent with Grebe chondrodysplasia. The other members of the family have brachydactyly, radiologically characterised by short first metacarpals and short middle phalanges of the index and little fingers. The possibility of association of familial brachydactyly and Grebe chondrodysplasia is discussed. An attempt has been made to deal with the genetic counselling problem in this particular family.

Segregation of ABO, AK1 and ACONs in families with abnormalities of chromosome 9.

Some families with abnormalities of chromosome 9 have been combined with others from the literature to show that AK1 and ABO must lie near the end of that chromosome. Current evidence suggests that both lie in band 9q34. MNSs, GPT and Gc can be excluded from chromosome 9.

Multiple congenital defects associated with trisomy for long arm of No. 4.

The clinical and cytogenetic findings of a male infant with multiple congenital anomalies and trisomy for the distal third of the long arm of No. 4 are described. The abnormal chromosome was inherited from the mother who had a balanced translocation, t(4;9)(q31;q34). Trisomy for the long arm of No. 4 has previously been described in only 3 patients.