Daniela V. Luquetti

Microtia: Epidemiology and genetics†

Microtia is a congenital anomaly of the ear that ranges in severity from mild structural abnormalities to complete absence of the ear, and can occur as an isolated birth defect or as part of a spectrum of anomalies or a syndrome. Microtia is often associated with hearing loss and patients typically require treatment for hearing impairment and surgical ear reconstruction. The reported prevalence varies among regions, from 0.83 to 17.4 per 10,000 births, and the prevalence is considered to be higher in Hispanics, Asians, Native Americans, and Andeans. The etiology of microtia and the cause of this wide variability in prevalence are poorly understood. Strong evidence supports the role of environmental and genetic causes for microtia. Although some studies have identified candidate genetic variants for microtia, no causal genetic mutation has been confirmed. The application of novel strategies in developmental biology and genetics has facilitated elucidation of mechanisms controlling craniofacial development. In this paper we review current knowledge of the epidemiology and genetics of microtia, including potential candidate genes supported by evidence from human syndromes and animal models. We also discuss the possible etiopathogenesis in light of the hypotheses formulated to date: Neural crest cells disturbance, vascular disruption, and altitude.

Microtia‐anotia: A global review of prevalence rates

BACKGROUND There are few published studies on microtia-anotia frequency. METHODS Using data from birth defects surveillance programs around the world, we conducted a systematic review on the frequency of microtia-anotia to further explore the differences in prevalence across countries. Ninety-two birth defects surveillance programs were evaluated with a total of 8917 cases of microtia-anotia. We computed the prevalence per 10,000 births for each surveillance program for total cases of microtia-anotia (microtia types I to IV), microtia (types I to III), and anotia (type IV). Prevalence ratios were calculated by large geographic areas, race/ethnicity, and by surveillance methodologies. RESULTS The overall prevalences were: microtia-anotia, 2.06 (confidence interval [CI], 2.02-2.10); microtia, 1.55 (CI, 1.50-1.60); and anotia 0.36 (CI, 0.34-0.38). Higher prevalences were observed for the Americas, Northern Europe and Asia, among Hispanics and Asians, and among active ascertainment and hospital-based surveillance programs. CONCLUSIONS We observed marked variation in the prevalence of microtia-anotia across surveillance programs and within countries. These results must be interpreted cautiously as this variability may be explained mainly by differences in surveillance methods. However, given the magnitude of some of the differences, other factors may also be involved. This study contributes to the knowledge of the prevalence of microtia-anotia by providing a critical analysis of the existing data. In addition, it supports the need for a coding system that allows complete phenotype characterization of microtia-anotia, including severity and laterality, as well as for further studies on the variation of its frequency related to race and ethnicity.

Mandibulofacial dysostosis with microcephaly caused by EFTUD2 mutations: expanding the phenotype.

Heterozygous mutations in the EFTUD2 were identified in 12 individuals with a rare sporadic craniofacial condition termed Mandibulofacial dysostosis with microcephaly (MIM 610536). We present clinical and radiographic features of three additional patients with de novo heterozygous mutations in EFTUD2. Although clinical features overlap with findings of the original report (choanal atresia, cleft palate, maxillary and mandibular hypoplasia, and microtia), microcephaly was present in two of three patients and cognitive impairment was milder in those with head circumference proportional to height. Our cases expand the phenotypic spectrum to include epibulbar dermoids and zygomatic arch clefting. We suggest that craniofacial computed tomography studies to assess cleft of zygomatic arch may assist in making this diagnosis. We recommend consideration of EFTUD2 testing in individuals with features of oculo‐auriculo‐vertebral spectrum and bilateral microtia, or individuals with atypical CHARGE syndrome who do not have a CHD7 mutation, particularly those with a zygomatic arch cleft. The absence of microcephaly in one patient indicates that it is a highly variable phenotypic feature.

Quality of reporting on birth defects in birth certificates: case study from a Brazilian reference hospital

The aim of this study was to evaluate the coverage, validity and reliability of Brazils Information System on Live Births (SINASC) for birth defects in a hospital in the city of Campinas (São Paulo State). The study population consisted of 2,823 newborn infants delivered in 2004 at the Womens Integrated Health Care Center (CAISM). A birth defect registry (ECLAMC) was used as the gold-standard. All birth defect cases reported at CAISM in 2004 (92 cases) were selected from SINASC data files. All 168 birth defect cases from the same city and year registered at ECLAMC were also retrieved. An underreporting of 46.8% was observed for all birth defects, and 36.4% when considering only the major birth defects. The ascertained sensitivity and specificity were, respectively, 54.2% and 99.8%. The reliability of three and four-digit ICD-10 coding for birth defects was 0.77 and 0.55 respectively (kappa statistic). These results suggest that information provided by birth certificates in Campinas still presents limitations when seeking to ascertain accurate estimates of the prevalence of birth defects, hence indicating the need for improvements in the SINASC database to enable it to portray birth defect prevalence at birth in this city.

The genetics of auricular development and malformation: new findings in model systems driving future directions for microtia research.

Microtia is a term used to describe a wide array of phenotypic presentations of the outer ear. Although the majority of the cases are isolated in nature, much of our understanding of the causes of microtia has been driven by the identification of genes underlying syndromic forms where the anomaly co-presents with various other craniofacial and extra-craniofacial structural defects. In this review we discuss recent findings in mice deficient in Hoxa2, a key regulator of branchial arch patterning, which has necessitated a revision to the canonical model of pinna morphogenesis. The revised model will likely impact current classification schemes for microtia and, as we argue in this review, the interpretation of the developmental basis for various auricular malformations. In addition, we highlight recent studies in other mammalian species that are providing the first clues as to possible causes of at least some isolated anomalies and thus should now accelerate the search for the more elusive genetic contributions to the many isolated and non-syndromic cases of microtia. These findings, together with the application of new genome-level sequencing technologies and more thorough quantitative assessment of available mutant mouse resources, promise an exciting future for genetic studies in microtia.

A phenotypic assessment tool for craniofacial microsomia.

Background: Craniofacial microsomia is one of the most common conditions treated by craniofacial teams. However, research regarding the cause of this condition or the surgical outcomes of treatment is scant. This is attributable to the lack of diagnostic criteria and the wide phenotypic spectrum. Standardized description of the craniofacial malformations associated with craniofacial microsomia is a necessary first step for multicenter, interdisciplinary research into this complex condition. Methods: The authors used the previously published pictorial Orbit, Mandible, Ear, Nerve, and Soft tissue–Plus classification scheme to assign a phenotypic severity score to patients with craniofacial microsomia treated at the Craniofacial Center at Seattle Childrens Hospital. The authors modified the tool based on feedback from multidisciplinary focus groups. The authors also developed a standardized photographic protocol to facilitate assessment of patients using two-dimensional images. Results: Feedback from focus groups was synthesized to create a phenotypic assessment tool for craniofacial microsomia based on the pictorial Orbit, Mandible, Ear, Nerve, and Soft tissue–Plus classification system. This tool allows for more comprehensive description of the phenotype of craniofacial microsomia and is found to be effective for clinical use within a multidisciplinary craniofacial team. In addition, the photographic protocol for patients with craniofacial microsomia allows for classification from a two-dimensional photographic database, thereby facilitating research using archived photographs. Conclusions: The phenotypic assessment tool for craniofacial microsomia protocol provides a simple and standardized method for practitioners and researchers to classify patients with craniofacial microsomia. We anticipate that this tool can be used in multicenter investigational studies to evaluate the cause of this condition, its natural history, and comparative effectiveness research.

Fraser and Ablepharon macrostomia phenotypes: Concurrence in one family and association with mutated FRAS1†

To date, Fraser syndrome (FS) and Ablepharon macrostomia syndrome (AMS) have been considered distinct disorders, but they share strikingly similar patterns of congenital abnormalities, specifically craniofacial anomalies. While recent research has led to the identification of the genes FRAS1 and FREM2 as the cause of FS, the genetic basis of AMS continues to be enigmatic. We report on the concurrence of AMS‐like and Fraser phenotypes in a Brazilian family. Both affected sibs were homozygous for a novel splice site mutation in the FRAS1 gene. Extensive studies on mRNA expression indicated that this mutation most likely leads to loss of function as most previously reported FRAS1 mutations associated with FS. We conclude that a phenotype resembling AMS is a rare clinical expression of FS with no obvious genotype–phenotype correlation. However, the molecular basis of “true” AMS which has been reported as a sporadic disorder in all cases but one, and so far with no relation to FS, is probably different and still needs to be further investigated.

Clinical care in craniofacial microsomia: a review of current management recommendations and opportunities to advance research.

Craniofacial microsomia (CFM) is a complex condition associated with microtia, mandibular hypoplasia, and preauricular tags. It is the second most common congenital facial condition treated in many craniofacial centers and requires longitudinal multidisciplinary patient care. The purpose of this article is to summarize current recommendations for clinical management and discuss opportunities to advance clinical research in CFM.

Qualidade da notificação de anomalias congênitas pelo Sistema de Informações sobre Nascidos Vivos (SINASC): estudo comparativo nos anos 2004 e 2007

This study compared the validity of birth defect cases reported in the Brazilian Information System on Live Births in 2004 and 2007 in seven municipalities, out of a total of 27,945 live births in 2004 and 25,905 in 2007. The study also describes quality improvement measures in this area. The Latin American Collaborative Study on Congenital Malformations was used as the gold standard for analyzing the validity of birth defect diagnoses. In 2004, at least 40% of birth defects went unreported, and this situation persisted in 2007. Only one hospital showed a significant increase in reporting sensitivity, from 56.9% to 96.8%. Sensitivity decreased significantly in two hospitals (from 62.7% to 41.75% and from 66.5% to 32.2%, respectively). The positive and negative predictive values and specificity remained above 80%. Only two municipal health departments and four hospitals implemented measures to improve reporting of birth defects. The results indicate the need for investments in the quality of birth defect information on birth certificates.

Deletion of a conserved regulatory element required for Hmx1 expression in craniofacial mesenchyme in the dumbo rat: a newly identified cause of congenital ear malformation

SUMMARY Hmx1 is a homeodomain transcription factor expressed in the developing eye, peripheral ganglia, and branchial arches of avian and mammalian embryos. Recent studies have identified a loss-of-function allele at the HMX1 locus as the causative mutation in the oculo-auricular syndrome (OAS) in humans, characterized by ear and eye malformations. The mouse dumbo (dmbo) mutation, with similar effects on ear and eye development, also results from a loss-of-function mutation in the Hmx1 gene. A recessive dmbo mutation causing ear malformation in rats has been mapped to the chromosomal region containing the Hmx1 gene, but the nature of the causative allele is unknown. Here we show that dumbo rats and mice exhibit similar neonatal ear and eye phenotypes. In midgestation embryos, dumbo rats show a specific loss of Hmx1 expression in neural-crest-derived craniofacial mesenchyme (CM), whereas Hmx1 is expressed normally in retinal progenitors, sensory ganglia and in CM, which is derived from mesoderm. High-throughput resequencing of 1 Mb of rat chromosome 14 from dmbo/dmbo rats, encompassing the Hmx1 locus, reveals numerous divergences from the rat genomic reference sequence, but no coding changes in Hmx1. Fine genetic mapping narrows the dmbo critical region to an interval of ∼410 kb immediately downstream of the Hmx1 transcription unit. Further sequence analysis of this region reveals a 5777-bp deletion located ∼80 kb downstream in dmbo/dmbo rats that is not apparent in 137 other rat strains. The dmbo deletion region contains a highly conserved domain of ∼500 bp, which is a candidate distal enhancer and which exhibits a similar relationship to Hmx genes in all vertebrate species for which data are available. We conclude that the rat dumbo phenotype is likely to result from loss of function of an ultraconserved enhancer specifically regulating Hmx1 expression in neural-crest-derived CM. Dysregulation of Hmx1 expression is thus a candidate mechanism for congenital ear malformation, most cases of which remain unexplained.