Anna L. Mitchell

Regions of homozygosity identified by SNP microarray analysis aid in the diagnosis of autosomal recessive disease and incidentally detect parental blood relationships

Purpose:The purpose of this study was to document the ability of single-nucleotide polymorphism microarray to identify copy-neutral regions of homozygosity, demonstrate clinical utility of regions of homozygosity, and discuss ethical/legal implications when regions of homozygosity are associated with a parental blood relationship.Methods:Study data were compiled from consecutive samples sent to our clinical laboratory over a 3-year period. A cytogenetics database identified patients with at least two regions of homozygosity >10 Mb on two separate chromosomes. A chart review was conducted on patients who met the criteria.Results:Of 3,217 single-nucleotide polymorphism microarrays, 59 (1.8%) patients met inclusion criteria. The percentage of homozygosity ranged from 0.9 to 30.1%, indicating parental relationships from distant to first-degree relatives. First-degree kinship was suspected in the parents of at least 11 patients with regions of homozygosity covering >21.3% of their autosome. In four patients from two families, homozygosity mapping discovered a candidate gene that was sequenced to identify a clinically significant mutation.Conclusion:This study demonstrates clinical utility in the identification of regions of homozygosity, as these regions may aid in diagnosis of the patient. This study establishes the need for careful reporting, thorough pretest counseling, and careful electronic documentation, as microarray has the capability of detecting previously unknown/unreported relationships.Genet Med 2013:15(1):70–78

An Xp; Yq Translocation Causing a Novel Contiguous Gene Syndrome in Brothers with Generalized Epilepsy, Ichthyosis, and Attention Deficits

Summary:  Purpose: We describe two brothers with generalized epilepsy, attention deficits, congenital ichthyosis, and Leri–Weill dyschondrosteosis who harbor an unusual Xp; Yq translocation chromosome, resulting in a novel contiguous gene syndrome because of deletion of genes from the distal short arm of the X chromosome.

Molecular mechanisms of classical Ehlers-Danlos syndrome (EDS)

Classical Ehlers‐Danlos syndrome (EDS) is a heritable disorder characterized by joint hypermobility, skin hyperextensibility, and abnormal wound healing. The majority of affected individuals have alterations in 1 of the 2 type V collagen genes, COL5A1 and COL5A2. The most common mechanism is COL5A1 haploinsufficiency due to instability of the transcript of one allele. In dermal fibroblasts from our population of 76 individuals with clinical features of classical EDS, there were 21 (29.5%) with decreased expression of one COL5A1 allele, consistent with published estimates of the frequency of null alleles. We identified the causative mutation in nine of these cell strains (mutations for seven others had been previously described), and found two nonsense mutations, five splice mutations, and two insertion/deletions. The same type of genomic change at splice sites can have different effects at the RNA level and the outcome could not be predicted from the primary genomic DNA alteration. Hum Mutat 30:1–8, 2009.

Effects of pregnancy on the renal and pulmonary manifestations in women with tuberous sclerosis complex

Effects of pregnancy on the renal and pulmonary manifestations in women with tuberous sclerosis complex

Pathogenic FBN1 variants in familial thoracic aortic aneurysms and dissections.

Marfan syndrome (MFS) due to mutations in FBN1 is a known cause of thoracic aortic aneurysms and acute aortic dissections (TAAD) associated with pleiotropic manifestations. Genetic predisposition to TAAD can also be inherited in families in the absence of syndromic features, termed familial TAAD (FTAAD), and several causative genes have been identified to date. FBN1 mutations can also be identified in FTAAD families, but the frequency of these mutations has not been established. We performed exome sequencing of 183 FTAAD families and identified pathogenic FBN1 variants in five (2.7%) of these families. We also identified eight additional FBN1 rare variants that could not be unequivocally classified as disease‐causing in six families. FBN1 sequencing should be considered in individuals with FTAAD even without significant systemic features of MFS.

Ventilatory pattern and energy expenditure are altered in cystic fibrosis mice.

BACKGROUND Altered ventilatory pattern and increased energy expenditure are facets of the complex cystic fibrosis (CF) phenotype. It is not known whether these are inherent attributes of CF, secondary consequences of lung infection or other disease complications. METHODS Studies were performed in congenic C57BL/6J, F508del (Cftr((tm1kth))) and CF gut-corrected (F508del) mice. Ventilatory patterns were measured using whole-body plethysmography. Indirect calorimetry was used to determine oxygen consumption, carbon dioxide production and resting energy expenditure. RESULTS CF mice (F508del and F508del gut-corrected) have a significantly faster respiratory rate and increased ventilatory pattern variability as compared to non-CF mice. F508del but not CF gut-corrected mice had significantly increased energy expenditure per gram body weight. CONCLUSIONS CF mice exhibit a faster, more variable ventilatory pattern. These changes were present in the absence of detectable infection or illness due to gastrointestinal obstruction. Increased resting energy expenditure does not completely account for these differences.

Early pulmonary disease manifestations in cystic fibrosis mice

BACKGROUND Altered pulmonary function is present early in the course of cystic fibrosis (CF), independent of documented infections or onset of pulmonary symptoms. New initiatives in clinical care are focusing on detection and characterization of preclinical disease. Thus, animal models are needed which recapitulate the pulmonary phenotype characteristic of early stage CF. METHODS We investigated young CF mice to determine if they exhibit pulmonary pathophysiology consistent with the early CF lung phenotype. Lung histology and pulmonary mechanics were examined in 12- to 16-week-old congenic C57bl/6 F508del and R117H CF mice using a forced oscillation technique (flexiVent). RESULTS There were no significant differences in the resistance of the large airways. However, in both CF mouse models, prominent differences in the mechanical properties of the peripheral lung compartment were identified including decreased static lung compliance, increased elastance and increased tissue damping. CF mice also had distal airspace enlargement with significantly increased mean linear intercept distances. CONCLUSIONS An impaired ability to stretch and expand the peripheral lung compartment, as well as increased distances between gas exchange surfaces, were present in young CF mice carrying two independent Cftr mutations. This altered pulmonary histopathophysiology in the peripheral lung compartment, which develops in the absence of infection, is similar to the early lung phenotype of CF patients.

Moyamoya disease associated with asymptomatic mosaic turner syndrome: A rare cause of hemorrhagic stroke

Moyamoya disease is a rare cerebrovascular anomaly involving the intracranial carotid arteries that can present clinically with either ischemic or hemorrhagic disease. Moyamoya syndrome, indistinguishable from moyamoya disease at presentation, is associated with multiple clinical conditions including neurofibromatosis type 1, autoimmune disease, prior radiation therapy, Down syndrome, and Turner syndrome. We present the first reported case of an adult patient with previously unrecognized mosaic Turner syndrome with acute subarachnoid and intracerebral hemorrhage as the initial manifestation of moyamoya syndrome. A 52-year-old woman was admitted with a subarachnoid hemorrhage with associated flame-shaped intracerebral hemorrhage in the left frontal lobe. Physical examination revealed short stature, pectus excavatum, small fingers, micrognathia, and mild facial dysmorphism. Cerebral angiography showed features consistent with bilateral moyamoya disease, aberrant intrathoracic vessels, and an unruptured 4-mm right superior hypophyseal aneurysm. Genetic analysis confirmed a diagnosis of mosaic Turner syndrome. Our case report is the first documented presentation of adult moyamoya syndrome with subarachnoid and intracerebral hemorrhage as the initial presentation of mosaic Turner syndrome. It illustrates the utility of genetic evaluation in patients with cerebrovascular disease and dysmorphism.

Microarray comparative genomic hybridization and cytogenetic characterization of tissue-specific mosaicism in three patients.

The presence of more than one cell line in an individual may often be missed by classical cytogenetic analysis due to a low percentage of affected cells or analysis of cells from an unaffected or less affected germ layer. Array comparative genomic hybridization (aCGH) from whole blood or tissue is an important adjunct to standard karyotyping due to its ability to detect genomic imbalances that are below the resolution of karyotype analysis. We report results from three unrelated patients in whom aCGH revealed mosaicism not identified by peripheral blood chromosome analysis. This study further illustrates the important application of aCGH in detecting tissue‐specific mosaicism, thereby leading to an improvement in the ability to provide a diagnosis for patients with normal chromosome analysis and dysmorphic features, congenital anomalies, and/or developmental delay.

AGTR2 absence or antagonism prevents cystic fibrosis pulmonary manifestations

BACKGROUND Pulmonary disease remains the primary cause of morbidity and mortality for individuals with cystic fibrosis (CF). Variants at a locus on the X-chromosome containing the type 2 angiotensin II receptor gene (AGTR2) were identified by a large GWAS as significantly associating with lung function in CF patients. We hypothesized that manipulating the angiotensin-signaling pathway may yield clinical benefit in CF. METHODS Genetic subset analysis was conducted on a local CF cohort to extend the GWAS findings. Next, we evaluated pulmonary function in CF mice with a deleted AGTR2 gene, and in those who were given subcutaneous injections of PD123,319, a selective AGTR2 antagonist for 12 weeks beginning at weaning. RESULTS The genetic subset analysis replicated the initial GWAS identified association, and confirmed the association of this locus with additional lung function parameters. Studies in genetically modified mice established that absence of the AGTR2 gene normalized pulmonary function indices in two independent CF mouse models. Further, we determined that pharmacologic antagonism of AGTR2 improved overall pulmonary function in CF mice to near wild-type levels. CONCLUSIONS These results identify that reduced AGTR2 signaling is beneficial to CF lung function, and suggest the potential of manipulating the angiotensin-signaling pathway for treatment and/or prevention of CF pulmonary disease. Importantly, the beneficial effects were not CF gene mutation dependent, and were able to be reproduced with pharmacologic antagonism. As there are clinically approved drugs available to target the renin-angiotensin signaling system, these findings may be quickly translated to human clinical trials.