Barbara R. Pober

Mutations in IRF6 cause Van der Woude and popliteal pterygium syndromes

Interferon regulatory factor 6 (IRF6) belongs to a family of nine transcription factors that share a highly conserved helix–turn–helix DNA-binding domain and a less conserved protein-binding domain. Most IRFs regulate the expression of interferon-α and -β after viral infection, but the function of IRF6 is unknown. The gene encoding IRF6 is located in the critical region for the Van der Woude syndrome (VWS; OMIM 119300) locus at chromosome 1q32–q41 (refs 2,3). The disorder is an autosomal dominant form of cleft lip and palate with lip pits, and is the most common syndromic form of cleft lip or palate. Popliteal pterygium syndrome (PPS; OMIM 119500) is a disorder with a similar orofacial phenotype that also includes skin and genital anomalies. Phenotypic overlap and linkage data suggest that these two disorders are allelic. We found a nonsense mutation in IRF6 in the affected twin of a pair of monozygotic twins who were discordant for VWS. Subsequently, we identified mutations in IRF6 in 45 additional unrelated families affected with VWS and distinct mutations in 13 families affected with PPS. Expression analyses showed high levels of Irf6 mRNA along the medial edge of the fusing palate, tooth buds, hair follicles, genitalia and skin. Our observations demonstrate that haploinsufficiency of IRF6 disrupts orofacial development and are consistent with dominant-negative mutations disturbing development of the skin and genitalia.

Williams–Beuren Syndrome

Williams–Beuren syndrome, a multisystem disorder caused by the deletion of a chromosome region of 1.5 million to 1.8 million base pairs containing 26 to 28 genes, is a disorder of microdeletion or contiguous gene deletion. This review covers current understanding of the biology of this disorder.

A 1.5 million-base pair inversion polymorphism in families with williams-Beuren syndrome

Williams-Beuren syndrome (WBS) is most often caused by hemizygous deletion of a 1.5-Mb interval encompassing at least 17 genes at 7q11.23 (refs. 1,2). As with many other haploinsufficiency diseases, the mechanism underlying the WBS deletion is thought to be unequal meiotic recombination, probably mediated by the highly homologous DNA that flanks the commonly deleted region. Here, we report the use of interphase fluorescence in situ hybridization (FISH) and pulsed-field gel electrophoresis (PFGE) to identify a genomic polymorphism in families with WBS, consisting of an inversion of the WBS region. We have observed that the inversion is hemizygous in 3 of 11 (27%) atypical affected individuals who show a subset of the WBS phenotypic spectrum but do not carry the typical WBS microdeletion. Two of these individuals also have a parent who carries the inversion. In addition, in 4 of 12 (33%) families with a proband carrying the WBS deletion, we observed the inversion exclusively in the parent transmitting the disease-related chromosome. These results suggest the presence of a newly identified genomic variant within the population that may be associated with the disease. It may result in predisposition to primarily WBS-causing microdeletions, but may also cause translocations and inversions.

Mutations in LRP2 , which encodes the multiligand receptor megalin, cause Donnai-Barrow and facio-oculo-acoustico-renal syndromes

Donnai-Barrow syndrome is associated with agenesis of the corpus callosum, congenital diaphragmatic hernia, facial dysmorphology, ocular anomalies, sensorineural hearing loss and developmental delay. By studying multiplex families, we mapped this disorder to chromosome 2q23.3–31.1 and identified LRP2 mutations in six families with Donnai-Barrow syndrome and one family with facio-oculo-acoustico-renal syndrome. LRP2 encodes megalin, a multiligand uptake receptor that regulates levels of diverse circulating compounds. This work implicates a pathway with potential pharmacological therapeutic targets.

Multisystem study of 20 older adults with Williams syndrome

To address the natural history of Williams syndrome (WS), we performed multisystem assessments on 20 adults with WS over 30 years of age and documented a high frequency of problems in multiple organ systems. The most striking and consistent findings were: abnormal body habitus; mild–moderate high frequency sensorineural hearing loss; cardiovascular disease and hypertension; gastrointestinal symptoms including diverticular disease; diabetes and abnormal glucose tolerance on standard oral glucose tolerance testing; subclinical hypothyroidism; decreased bone mineral density on DEXA scanning; and a high frequency of psychiatric symptoms, most notably anxiety, often requiring multimodal therapy. Review of brain MRI scans did not demonstrate consistent pathology. The adults in our cohort were not living independently and the vast majority were not competitively employed. Our preliminary findings raise concern about the occurrence of mild accelerated aging, which may additionally complicate the long‐term natural history of older adults with WS. We provide monitoring guidelines to assist in the comprehensive care of adults with WS.

GATA4 haploinsufficiency in patients with interstitial deletion of chromosome region 8p23.1 and congenital heart disease

Previous studies have shown that patients with deletion of distal human chromosome arm 8p may have congenital heart disease and other physical anomalies. The gene encoding GATA-4, a zinc finger transcription factor implicated in cardiac gene expression and development, localizes to chromosome region 8p23.1. To examine whether GATA-4 deficiency is present in patients with monosomy of 8p23.1 with congenital heart disease, we performed fluorescence in situ hybridization (FISH) with a GATA4 probe on cells from a series of patients with interstitial deletion of 8p23.1. Four individuals with del(8)(p23.1) and congenital heart disease were found to be haploinsufficient at the GATA4 locus by FISH. The GATA4 gene was not deleted in a fifth patient with del(8)(p23.1) who lacked cardiac anomalies. FISH analysis on cells from 48 individuals with congenital heart disease and normal karyotypes failed to detect any submicroscopic deletions at the GATA4 locus. We conclude that haploinsufficiency at the GATA4 locus is often seen in patients with del(8)(p23.1) and congenital heart disease. Based on these findings and recent studies showing that haploinsufficiency for other cardiac transcription factor genes (e.g., TBX5, NKX2-5) causes congenital heart disease, we postulate that GATA-4 deficiency may contribute to the phenotype of patients with monosomy of 8p23.1.

Fog2 Is Required for Normal Diaphragm and Lung Development in Mice and Humans

Congenital diaphragmatic hernia and other congenital diaphragmatic defects are associated with significant mortality and morbidity in neonates; however, the molecular basis of these developmental anomalies is unknown. In an analysis of E18.5 embryos derived from mice treated with N-ethyl-N-nitrosourea, we identified a mutation that causes pulmonary hypoplasia and abnormal diaphragmatic development. Fog2 (Zfpm2) maps within the recombinant interval carrying the N-ethyl-N-nitrosourea-induced mutation, and DNA sequencing of Fog2 identified a mutation in a splice donor site that generates an abnormal transcript encoding a truncated protein. Human autopsy cases with diaphragmatic defect and pulmonary hypoplasia were evaluated for mutations in FOG2. Sequence analysis revealed a de novo mutation resulting in a premature stop codon in a child who died on the first day of life secondary to severe bilateral pulmonary hypoplasia and an abnormally muscularized diaphragm. Using a phenotype-driven approach, we have established that Fog2 is required for normal diaphragm and lung development, a role that has not been previously appreciated. FOG2 is the first gene implicated in the pathogenesis of nonsyndromic human congenital diaphragmatic defects, and its necessity for pulmonary development validates the hypothesis that neonates with congenital diaphragmatic hernia may also have primary pulmonary developmental abnormalities.

Discriminating power of localized three-dimensional facial morphology

Many genetic syndromes involve a facial gestalt that suggests a preliminary diagnosis to an experienced clinical geneticist even before a clinical examination and genotyping are undertaken. Previously, using visualization and pattern recognition, we showed that dense surface models (DSMs) of full face shape characterize facial dysmorphology in Noonan and in 22q11 deletion syndromes. In this much larger study of 696 individuals, we extend the use of DSMs of the full face to establish accurate discrimination between controls and individuals with Williams, Smith-Magenis, 22q11 deletion, or Noonan syndromes and between individuals with different syndromes in these groups. However, the full power of the DSM approach is demonstrated by the comparable discriminating abilities of localized facial features, such as periorbital, perinasal, and perioral patches, and the correlation of DSM-based predictions and molecular findings. This study demonstrates the potential of face shape models to assist clinical training through visualization, to support clinical diagnosis of affected individuals through pattern recognition, and to enable the objective comparison of individuals sharing other phenotypic or genotypic properties.

Mechanisms and treatment of cardiovascular disease in Williams-Beuren syndrome

Williams-Beuren syndrome (WBS) is a microdeletion disorder caused by heterozygous loss of approximately 1.5-Mb pairs of DNA from chromosome 7. Patients with WBS have a characteristic constellation of medical and cognitive findings, with a hallmark feature of generalized arteriopathy presenting as stenoses of elastic arteries and hypertension. Human and mouse studies establish that defects in the elastin gene, leading to elastin haploinsufficiency, underlie the arteriopathy. In this review we describe potential links between elastin expression and arteriopathy, possible explanations for disease variability, and current treatment options and their limitations, and we propose several new directions for the development of nonsurgical preventative therapies based on insights from elastin biology.

Overview of Epidemiology, Genetics, Birth Defects, and Chromosome Abnormalities Associated With CDH

Congenital diaphragmatic hernia (CDH) is a common and well‐studied birth defect. The etiology of most cases remains unknown but increasing evidence points to genetic causation. The data supporting genetic etiologies which are detailed below include the association of CDH with recurring chromosome abnormalities, the existence of CDH‐multiplex families, and the co‐occurrence of CDH with additional congenital malformations.