Correlation of cord blood pH, base excess, and lactate concentration measured with a portable device for identifying fetal acidosis

OBJECTIVE

To determine the effectiveness of portable lactate analyzers in identifying fetal acidosis by correlating arterial and venous lactate values from umbilical cord blood with lactate, pH, and base excess measurements from central laboratory analyzers.

METHODS

We performed a prospective study using arterial and venous cord blood from 52 women with a singleton fetus delivered at term. We evaluated the correlation between the cord blood lactate concentration measured using two of the same portable devices (Lactate Plus, Nova Biomedical) with the result from a central laboratory analyzer. Analyses of the correlation between arterial lactate concentration measured on the portable device with arterial pH and base excess were then performed.

RESULTS

We observed a median arterial pH of 7.24 (range 7.05 to 7.35) and a median arterial lactate concentration of 3.7 mmol/L (range 1.7 to 8.8 mmol/L). An excellent correlation was observed between lactate concentrations measured by the two portable devices (arterial R² = 0.98 and venous R² = 0.98), and between the portable device and the central laboratory analyzer (arterial R² = 0.94 and venous R² = 0.95). In our population, the optimal cut-offs to predict a pH < 7.20 or a base excess > -8.0 mmol/L were a lactate concentration of 4.9 mmol/L and 5.3 mmol/L, respectively, according to receiver operator characteristic analysis. With a lactate concentration > 4.9 mmol/L, the portable device had a sensitivity of 82% and a specificity of 90% to identify samples with an arterial pH < 7.20.

CONCLUSION

Cord blood lactate concentration measured with a portable device is a good predictor of cord blood base excess and pH. Future studies should be designed to correlate scalp blood lactate measurements with clinical outcomes.

Mutations in NOTCH2 in families with Hajdu-Cheney syndrome

Hajdu-Cheney syndrome (HCS) is a rare genetic disorder whose hallmark is acro-osteolysis, shortening of terminal phalanges, and generalized osteoporosis. We assembled a cohort of seven families with the condition and performed whole exome resequencing on a selected set of affected patients. One protein-coding gene, NOTCH2, carried heterozygous truncating variants in all patients and their affected family members. Our results replicate recently published studies of HCS and further support this as the causal gene for the disorder. In total, we identified five novel and one previously reported mutation, all clustered near the carboxyl terminus of the gene, suggesting an allele specific genotype-phenotype effect since other mutations in NOTCH2 have been reported to cause a form of Alagille syndrome. Notch-mediated signaling is known to play a role in bone metabolism. Our results support a potential therapeutic role for Notch pathways in treatment of osteoporosis.

Mutations in a novel serine protease PRSS56 in families with nanophthalmos

PURPOSE

Nanophthalmos is a rare genetic ocular disorder in which the eyes of affected individuals are abnormally small. Patients suffer from severe hyperopia as a result of their markedly reduced axial lengths, but otherwise are capable of seeing well unlike other more general forms of microphthalmia. To date one gene for nanophthalmos has been identified, encoding the membrane-type frizzled related protein MFRP. Identification of additional genes for nanophthalmos will improve our understanding of normal developmental regulation of eye growth.

METHODS

We ascertained a cohort of families from eastern Canada and Mexico with familial nanophthalmos. We performed high density microsatellite and high density single nucleotide polymorphism (SNP) genotyping to identify potential chromosomal regions of linkage. We sequenced coding regions of genes in the linked interval by traditional PCR-based Sanger capillary electrophoresis methods. We cloned and sequenced a novel cDNA from a putative causal gene to verify gene structure.

RESULTS

We identified a linked locus on chromosome 2q37 with a peak logarithm (base 10) of odds (LOD) score of 4.7. Sequencing of coding exons of all genes in the region identified multiple segregating variants in one gene, recently annotated as serine protease gene (PRSS56), coding for a predicted trypsin serine protease-like protein. One of our families was homozygous for a predicted pathogenic missense mutation, one family was compound heterozygous for two predicted pathogenic missense mutations, and one family was compound heterozygous for a predicted pathogenic missense mutation plus a frameshift leading to obligatory truncation of the predicted protein. The PRSS56 gene structure in public databases is based on a virtual transcript assembled from overlapping incomplete cDNA clones; we have now validated the structure of a full-length transcript from embryonic mouse brain RNA.

CONCLUSIONS

PRSS56 is a good candidate for the causal gene for nanophthalmos in our families.

Mice deficient in Neu4 sialidase exhibit abnormal ganglioside catabolism and lysosomal storage

Mammalian sialidase Neu4, ubiquitously expressed in human tissues, is located in the lysosomal and mitochondrial lumen and has broad substrate specificity against sialylated glycoconjugates. To investigate whether Neu4 is involved in ganglioside catabolism, we transfected beta-hexosaminidase-deficient neuroglia cells from a Tay-Sachs patient with a Neu4-expressing plasmid and demonstrated the correction of storage due to the clearance of accumulated GM2 ganglioside. To further clarify the biological role of Neu4, we have generated a stable loss-of-function phenotype in cultured HeLa cells and in mice with targeted disruption of the Neu4 gene. The silenced HeLa cells showed reduced activity against gangliosides and had large heterogeneous lysosomes containing lamellar structures. Neu4(-/-) mice were viable, fertile and lacked gross morphological abnormalities, but showed a marked vacuolization and lysosomal storage in lung and spleen cells. Lysosomal storage bodies were also present in cultured macrophages preloaded with gangliosides. Thin-layer chromatography showed increased relative level of GD1a ganglioside and a markedly decreased level of GM1 ganglioside in brain of Neu4(-/-) mice suggesting that Neu4 may be important for desialylation of brain gangliosides and consistent with the in situ hybridization data. Increased levels of cholesterol, ceramide and polyunsaturated fatty acids were also detected in the lungs and spleen of Neu4(-/-) mice by high-resolution NMR spectroscopy. Together, our data suggest that Neu4 is a functional component of the ganglioside-metabolizing system, contributing to the postnatal development of the brain and other vital organs.

Laminar organization of the early developing anterior hypothalamus

The bHLH-PAS transcription factor SIM1 is required for the development of neurons of the anterior hypothalamus (AH). In order to dissect this developmental program, we compared gene expression in the AH of E12.5 Sim1(+/+) and Sim1(-/-) littermates using an oligonucleotide-based microarray. Our analysis identified 48 genes that were downregulated and 8 genes that were upregulated. We examined the expression pattern of 10 of the identified genes--Cart, Cbln1, Alcam, Unc-13c, Rgs4, Lnx4, Irx3, Sax1, Ldb2 and Neurod6--by in situ hybridization in E12.5 embryos. All of these genes are expressed in domains that are contained within that of Sim1 and their expression is changed in Sim1(-/-) embryos as predicted by the microarray analysis. Classical dating studies have established that the hypothalamus follows an "outside-in" pattern of neurogenesis, with neurons of the lateral hypothalamus being born before the medial ones. Analysis of the genes identified in this microarray study showed that the developing AH is characterized by different layers of gene expression that most likely correspond to distinct waves of neurogenesis. In addition, our analysis suggests that Sim1 function is required for the production or the survival of postmitotic neurons as well as for correct positioning of AH neurons.

Sim1 and Sim2 are required for the correct targeting of mammillary body axons

The mammillary body (MB), and its axonal projections to the thalamus (mammillothalamic tract, MTT) and the tegmentum (mammillotegmental tract, MTEG), are components of a circuit involved in spatial learning. The bHLH-PAS transcription factors SIM1 and SIM2 are co-expressed in the developing MB. We have found that MB neurons are generated and that they survive at least until E18.5 in embryos lacking both Sim1 and Sim2 (Sim1(-/-);Sim2(-/-)). However, the MTT and MTEG are histologically absent in Sim1(-/-);Sim2(-/-) embryos, and are reduced in embryos lacking Sim1 but bearing one or two copies of Sim2, indicating a contribution of the latter to the development of MB axons. We have generated, by homologous recombination, a null allele of Sim1 (Sim1(tlz)) in which the tau-lacZ fusion gene was introduced, allowing the staining of MB axons. Consistent with the histological studies, lacZ staining showed that the MTT/MTEG is barely detectable in Sim1(tlz/tlz);Sim2(+/-) and Sim1(tlz/tlz);Sim2(-/-) brains. Instead, MB axons are splayed and grow towards the midline. Slit1 and Slit2, which code for secreted molecules that induce the repulsion of ROBO1-producing axons, are expressed in the midline at the level of the MB, whereas Robo1 is expressed in the developing MB. The expression of Rig-1/Robo3, a negative regulator of Slit signalling, is upregulated in the prospective MB of Sim1/Sim2 double mutants, raising the possibility that the growth of mutant MB axons towards the midline is caused by a decreased sensitivity to SLIT. Finally, we found that Sim1 and Sim2 act along compensatory, but not hierarchical, pathways, suggesting that they play similar roles in vivo.

Looking for trouble: a search for developmental defects of the hypothalamus

The hypothalamus is a critical integrator of several homeostatic processes that are required for the survival of vertebrates. Disruption of the development of the hypothalamus thus has the potential of perturbing important physiological processes with lifelong consequences. We review current knowledge about how cell types are specified and circuits are formed within the developing hypothalamus. We emphasize the potential clinical impact of the perturbations of these pathways using the regulation of energy balance as a model. We predict that disruption of hypothalamic development is a common, previously unsuspected cause of disorders of homeostatic processes such as obesity and high blood pressure.

Regionalization of the anterior hypothalamus in the chick embryo

Loss-of-function experiments in mice have shown that the transcription factors Sim1, Otp, Sim2, and Brn2 form a cascade essential for the differentiation of neuroendocrine cells of the anterior hypothalamus that produce vasopressin, oxytocin, somatostatin (SS), thyrotropin-releasing hormone (TRH), and corticotropin-releasing hormone (CRH). Very little is known about how the differentiation of these cell types is regulated in chick. Here, we report the cloning of the chick homolog of Otp. Moreover, we have systematically compared the expression of Sim1, Sim2, Brn2, and Otp with that of the markers of terminal differentiation TRH, SS, CRH, vasotocin, and mesotocin during development of chick embryos. We have found that the cell types studied generally develop in domains expressing these transcriptional regulators but that the pattern of neuronal differentiation and the spatial distribution of some regulators were not the same as in mice. Our results provide a framework useful for the functional analysis of hypothalamus development in chick.