Novel Method of Calculating Pulse Pressure Variation to Predict Fluid Responsiveness to Transfusion in Very Low Birth Weight Infants.

A novel technique was used to calculate pulse pressure variation. The algorithm reliably predicted fluid responsiveness to transfusion, with a receiver operating characteristic area under the curve of 0.89. This technique may assist clinicians in the management of fluids and vasoactive medications for premature infants.

Critical Closing Pressure by Diffuse Correlation Spectroscopy in a Neonatal Piglet Model.

The critical closing pressure (CrCP) of the cerebral vasculature is the arterial blood pressure (ABP) at which cerebral blood flow (CBF) ceases. Because the ABP of preterm infants is low and close to the CrCP, there is often no CBF during diastole. Thus, estimation of CrCP may become clinically relevant in preterm neonates. Transcranial Doppler (TCD) ultrasound has been used to estimate CrCP in preterm infants. Diffuse correlation spectroscopy (DCS) is a continuous, noninvasive optical technique that measures microvascular CBF. Our objective was to compare and validate CrCP measured by DCS versus TCD ultrasound. Hemorrhagic shock was induced in 13 neonatal piglets, and CBF was measured continuously by both modalities. CrCP was calculated using a model of cerebrovascular impedance, and CrCP determined by the two modalities showed good correlation by linear regression, median r 2 = 0.8 (interquartile range (IQR) 0.71-0.87), and Bland-Altman analysis showed a median bias of -3.5 (IQR -4.6 to -0.28). This is the first comparison of CrCP determined by DCS versus TCD ultrasound in a neonatal piglet model of hemorrhagic shock. The difference in CrCP between the two modalities may be due to differences in vasomotor tone within the microvasculature of the cerebral arterioles versus the macrovasculature of a major cerebral artery.

Observed and calculated cerebral critical closing pressure are highly correlated in preterm infants.

BACKGROUND: Cerebrovascular critical closing pressure (CrCP) is the arterial blood pressure (ABP) at which cerebral blood flow ceases. Preterm ABP is low and close to CrCP. The diastolic closing margin (diastolic ABP minus CrCP) has been associated with intraventricular hemorrhage in preterm infants. CrCP is estimated from middle cerebral artery cerebral blood flow velocity (CBFV) and ABP waveforms. However, these estimations have not been validated due to a lack of gold standard. Direct observation of the CrCP in preterm infants with hypotension is an opportunity to validate synchronously estimated CrCP. METHODS: ABP and CBFV tracings were obtained from 24 extremely low birth weight infants. Recordings where diastolic CBFV was zero were identified. The gold standard CrCP was delineated using piecewise regression of ABP and CBFV values paired by rank ordering and then estimated using a published formula. The measured and estimated values were compared using linear regression and Bland-Altman analysis. RESULTS: Linear regression showed a high degree of correlation between measured and calculated CrCP (r2 = 0.93). CONCLUSIONS: This is the first study to validate a calculated CrCP by comparing it to direct measurements of CrCP from preterm infants when ABP is lower than CrCP.

Penetrance of biallelic SMARCAL1 mutations is associated with environmental and genetic disturbances of gene expression.

Biallelic mutations of the DNA annealing helicase SMARCAL1 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a-like 1) cause Schimke immuno-osseous dysplasia (SIOD, MIM 242900), an incompletely penetrant autosomal recessive disorder. Using human, Drosophila and mouse models, we show that the proteins encoded by SMARCAL1 orthologs localize to transcriptionally active chromatin and modulate gene expression. We also show that, as found in SIOD patients, deficiency of the SMARCAL1 orthologs alone is insufficient to cause disease in fruit flies and mice, although such deficiency causes modest diffuse alterations in gene expression. Rather, disease manifests when SMARCAL1 deficiency interacts with genetic and environmental factors that further alter gene expression. We conclude that the SMARCAL1 annealing helicase buffers fluctuations in gene expression and that alterations in gene expression contribute to the penetrance of SIOD.

Gene clusters, molecular evolution and disease: a speculation.

Traditionally eukaryotic genes are considered independently expressed under the control of their promoters and cis-regulatory domains. However, recent studies in worms, flies, mice and humans have shown that genes co-habiting a chromatin domain or "genomic neighborhood" are frequently co-expressed. Often these co-expressed genes neither constitute part of an operon nor function within the same biological pathway. The mechanisms underlying the partitioning of the genome into transcriptional genomic neighborhoods are poorly defined. However, cross-species analyses find that the linkage among the co-expressed genes of these clusters is significantly conserved and that the expression patterns of genes within clusters have coevolved with the clusters. Such selection could be mediated by chromatin interactions with the nuclear matrix and long-range remodeling of chromatin structure. In the context of human disease, we propose that dysregulation of gene expression across genomic neighborhoods will cause highly pleiotropic diseases. Candidate genomic neighborhood diseases include the nuclear laminopathies, chromosomal translocations and genomic instability disorders, imprinting disorders of errant insulator function, syndromes from impaired cohesin complex assembly, as well as diseases of global covalent histone modifications and DNA methylation. The alteration of transcriptional genomic neighborhoods provides an exciting and novel model for studying epigenetic alterations as quantitative traits in complex common human diseases.

Neurologic phenotype of Schimke immuno-osseous dysplasia and neurodevelopmental expression of SMARCAL1.

Schimke immuno-osseous dysplasia (OMIM 242900) is an uncommon autosomal-recessive multisystem disease caused by mutations in SMARCAL1 (swi/snf-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a-like 1), a gene encoding a putative chromatin remodeling protein. Neurologic manifestations identified to date relate to enhanced atherosclerosis and cerebrovascular disease. Based on a clinical survey, we determined that half of Schimke immuno-osseous dysplasia patients have a small head circumference, and 15% have social, language, motor, or cognitive abnormalities. Postmortem examination of 2 Schimke immuno-osseous dysplasia patients showed low brain weights and subtle brain histologic abnormalities suggestive of perturbed neuron-glial migration such as heterotopia, irregular cortical thickness, incomplete gyral formation, and poor definition of cortical layers. We found that SMARCAL1 is highly expressed in the developing and adult mouse and human brain, including neural precursors and neuronal lineage cells. These observations suggest that SMARCAL1 deficiency may influence brain development and function in addition to its previously recognized effect on cerebral circulation.

Schimke immuno-osseous dysplasia: a cell autonomous disorder?

SMARCAL1 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a-like protein 1) encodes a SWI/SNF ATP-dependent chromatin remodeling protein. Mutations in SMARCAL1 cause the autosomal-recessive multisystem disorder Schimke immuno-osseous dysplasia (SIOD); this suggests that the SMARCAL1 protein is involved in the development or maintenance of multiple organs. Disease within these many tissues could arise by a cell autonomous or a cell non-autonomous mechanism. Consistent with a cell autonomous mechanism, we did not find any disease recurrence in transplanted organs or protection of other tissues by the organ grafts. In order to better understand the role of SMARCAL1 during normal development and in the pathogenesis of SIOD, we characterized the spatial and temporal expression of the murine homolog (Smarcal1). The Smarcal1 mRNA and protein were expressed throughout development and in all tissues affected in patients with SIOD including the bone, kidney, thymus, thyroid, tooth, bone marrow, hair, eye, and blood vessels. Significantly, the expression profile of Smarcal1 in the mouse has led us to reexamine and identify novel pathology in our patient population resulting in changes in the clinical management of SIOD. The expression of Smarcal1 in affected tissues and the non-recurrence of disease in grafted organs lead us to hypothesize a cell autonomous function for SMARCAL1 and to propose tissue-specific mechanisms for the pathophysiology of SIOD.

Association of migraine-like headaches with Schimke immuno-osseous dysplasia.

Schimke immuno-osseous dysplasia (SIOD) is characterized by spondyloepiphyseal dysplasia, nephropathy, and T-cell deficiency. SIOD is caused by mutations in the putative chromatin remodeling protein SMARCAL1. We report an 8-year-old boy with SIOD and recurrent, severe, refractory migraine-like headaches. Through a retrospective questionnaire-based study, we found that refractory and severely disabling migraine-like headaches occur in nearly half of SIOD patients. We have also found that the vasodilator minoxidil provided symptomatic relief for one patient. We hypothesize that these headaches may arise from an intrinsic vascular, neuroimmune, or neurovascular defect resulting from loss of SMARCAL1 function.

Advances in chromatin remodeling and human disease.

Epigenetic factors alter phenotype without changing genotype. A primary molecular mechanism underlying epigenetics is the alteration of chromatin structure by covalent DNA modifications, covalent histone modifications, and nucleosome reorganization. Remodeling of chromatin structure regulates DNA methylation, replication, recombination, and repair as well as gene expression. As these functions would predict, dysfunction of the proteins that remodel chromatin causes an array of multi-system disorders and neoplasias. Insights from these diseases suggest that during embryonic and fetal life, environmental distortions of chromatin remodeling encode a 'molecular memory' that predispose the individual to diseases in adulthood.