Margarida Venâncio

Clinical dividends from the molecular genetic diagnosis of craniosynostosis

A dozen years have passed since the first genetic lesion was identified in a family with craniosynostosis, the premature fusion of the cranial sutures. Subsequently, mutations in the FGFR2, FGFR3, TWIST1, and EFNB1 genes have been shown to account for ∼25% of craniosynostosis, whilst several additional genes make minor contributions. Using specific examples, we show how these discoveries have enabled refinement of information on diagnosis, recurrence risk, prognosis for mental development, and surgical planning. However, phenotypic variability can present a significant challenge to the clinical interpretation of molecular genetic tests. In particular, the difficulty of analyzing the complex interaction of genetic background and prenatal environment in determining clinical features, limits the value of identifying low penetrance mutations.

An explanation for another familial case of Rett syndrome: maternal germline mosaicism

Rett syndrome (RTT; OMIM#312750) is a severe neurodevelopmental disorder that affects mainly girls. It has an estimated incidence of 1:10 000–15 000 females. Mutations in the X-linked gene methyl CpG-binding protein 2 (MECP2) have been found in most patients. The most accepted explanation for the sex bias is that the Rett mutation in sporadic cases has its origin in the paternal germline X chromosome and can thus only be transmitted to females. The majority of cases are sporadic (99.5%) but some familial cases have been described. These cases can either be explained by germline mosaicism or by asymptomatic carrier mothers with skewing of X-inactivation towards the wild-type MECP2 allele. We describe one of the few familial cases of RTT in which a maternal germline mosaicism is the most likely explanation. The mutation p.Arg270fs (c.808delC) was identified in both a girl with classical RTT and her brother who had the severe neurological phenotype usually described in males. The mutation was absent in DNA extracted from blood of both parents. These type of events must be taken into consideration in the genetic counselling of families after the diagnosis of a first case of RTT in a female or a MECP2 mutation in a male.

Oculo-auriculo-vertebral spectrum: Clinical and molecular analysis of 51 patients.

INTRODUCTION Oculo-auriculo-vertebral spectrum (OAVS OMIM 164210) is a craniofacial developmental disorder affecting the development of the structures derived from the 1st and the 2nd branchial arches during embryogenesis, with consequential maxillary, mandibular, and ear abnormalities. The phenotype in OAVS is variable and associated clinical features can involve the cardiac, renal, skeletal, and central nervous systems. Its aetiology is still poorly understood. METHODS We have evaluated the clinical phenotypes of 51 previously unpublished patients with OAVS and their parents, and performed comparative genomic hybridization microarray studies to identify potential causative loci. RESULTS Of all 51 patients, 16 (31%) had a family history of OAVS. Most had no relevant pre-natal history and only 5 (10%) cases had a history of environmental exposures that have previously been described as risk factors for OAVS. In 28 (55%) cases, the malformations were unilateral. When the involvement was bilateral, it was asymmetric. Ear abnormalities were present in 47 (92%) patients (unilateral in 24; and bilateral in 23). Hearing loss was common (85%), mostly conductive, but also sensorineural, or a combination of both. Hemifacial microsomia was present in 46 (90%) patients (17 also presented facial nerve palsy). Ocular anomalies were present in 15 (29%) patients. Vertebral anomalies were confirmed in 10 (20%) cases; 50% of those had additional heart, brain and/or other organ abnormalities. Brain abnormalities were present in 5 (10%) patients; developmental delay was more common among these patients. Limb abnormalities were found in 6 (12%) patients, and urogenital anomalies in 5 (10%). Array-CGH analysis identified 22q11 dosage anomalies in 10 out of 22 index cases screened. DISCUSSION In this study we carried out in-depth phenotyping of OAVS in a large, multicentre cohort. Clinical characteristics are in line with those reported previously, however, we observed a higher incidence of hemifacial microsomia and lower incidence of ocular anomalies. Furthermore our data suggests that OAVS patients with vertebral anomalies or congenital heart defects have a higher frequency of additional brain, limb or other malformations. We had a higher rate of familial cases in our cohort in comparison with previous reports, possibly because these cases were referred preferentially to our genetic clinic where family members underwent examination. We propose that familial OAVS cases show phenotypic variability, hence, affected relatives might have been misclassified in previous reports. Moreover, in view of its phenotypic variability, OAVS is potentially a spectrum of conditions, which overlap with other conditions, such as mandibulofacial dysostosis. Array CGH in our cohort identified recurrent dosage anomalies on 22q11, which may contribute to, or increase the risk of OAVS. We hypothesize that although the 22q11 locus may harbour gene(s) or regulatory elements that play a role in the regulation of craniofacial symmetry and 1st and 2nd branchial arch development, OAVS is a heterogeneous condition and many cases have a multifactorial aetiology or are caused by mutations in as yet unidentified gene(s).

Neurodevelopmental disorders associated with dosage imbalance of ZBTB20 correlate with the morbidity spectrum of ZBTB20 candidate target genes

Background Recently, a number of patients have been described with structural rearrangements at 3q13.31, delineating a novel microdeletion syndrome with common clinical features including developmental delay and other neurodevelopmental disorders (NDD). A smallest region of overlapping deletions (SRO) involved five RefSeq genes, including the transcription factor gene ZBTB20 and the dopamine receptor gene DRD3, considered as candidate genes for the syndrome. Methods and results We used array comparative genomic hybridization and next-generation mate-pair sequencing to identify key structural rearrangements involving ZBTB20 in two patients with NDD. In a patient with developmental delay, attention-deficit hyperactivity disorder, psychosis, Tourette’s syndrome and autistic traits, a de novo balanced t(3;18) translocation truncated ZBTB20. The other breakpoint did not disrupt any gene. In a second patient with developmental delay and autism, we detected the first microdeletion at 3q13.31, which truncated ZBTB20 but did not involve DRD3 or the other genes within the previously defined SRO. Zbtb20 directly represses 346 genes in the developing murine brain. Of the 342 human orthologous ZBTB20 candidate target genes, we found 68 associated with NDD. Using chromatin immunoprecipitation and quantitative PCR, we validated the in vivo binding of Zbtb20 in evolutionary conserved regions in six of these genes (Cntn4, Gad1, Nrxn1, Nrxn3, Scn2a, Snap25). Conclusions Our study links dosage imbalance of ZBTB20 to a range of neurodevelopmental, cognitive and psychiatric disorders, likely mediated by dysregulation of multiple ZBTB20 target genes, and provides new knowledge on the genetic background of the NDD seen in the 3q13.31 microdeletion syndrome.

Autosomal Recessive Axonal Neuropathy With Neuromyotonia: A Rare Entity

BACKGROUND Autosomal recessive axonal neuropathy with neuromyotonia is a recently described entity associated to the HINT1 gene, encoding histidine triad nucleotide-binding protein 1. PATIENT The authors report a Portuguese 16-year-old girl of Roma ethnicity, descendant of consanguineous parents, with progressive distal muscular atrophy and weakness, beginning at age 6. After several years of extensive investigation with inconclusive results, clinical myotonia was identified. Electrophysiologic studies revealed neuromyotonia associated with a severe chronic predominantly motor axonal neuropathy and homozygous mutation (c.334 C > A, p.H112 N) in HINT1 was detected. CONCLUSION This report emphasizes the late onset of clinical myotonia essential to the diagnosis.

Mutations in the MECP2 Gene Are Not a Major Cause of Rett Syndrome-Like or Related Neurodevelopmental Phenotype in Male Patients

Rett syndrome is a genetic neurodevelopmental disorder that affects mainly girls, but mutations in the causative MECP2 gene have also been identified in boys with classic Rett syndrome and Rett syndrome-like phenotypes. We have studied a group of 28 boys with a neurodevelopmental disorder, 13 of which with a Rett syndrome-like phenotype; the patients had diverse clinical presentations that included perturbations of the autistic spectrum, microcephaly, mental retardation, manual stereotypies, and epilepsy. We analyzed the complete coding region of the MECP2 gene, including the detection of large rearrangements, and we did not detect any pathogenic mutations in the MECP2 gene in these patients, in whom the genetic basis of disease remained unidentified. Thus, additional genes should be screened in this group of patients.

Critical region in 2q31.2q32.3 deletion syndrome: Report of two phenotypically distinct patients, one with an additional deletion in Alagille syndrome region

BackgroundStandard cytogenetic analysis has revealed to date more than 30 reported cases presenting interstitial deletions involving region 2q31-q32, but with poorly defined breakpoints. After the postulation of 2q31.2q32.3 deletion as a clinically recognizable disorder, more patients were reported with a critical region proposed and candidate genes pointed out.ResultsWe report two female patients with de novo chromosome 2 cytogenetically visible deletions, one of them with an additional de novo deletion in chromosome 20p12.2p12.3. Patient I presents a 16.8 Mb deletion in 2q31.2q32.3 while patient II presents a smaller deletion of 7 Mb in 2q32.1q32.3, entirely contained within patient I deleted region, and a second 4 Mb deletion in Alagille syndrome region. Patient I clearly manifests symptoms associated with the 2q31.2q32.3 deletion syndrome, like the muscular phenotype and behavioral problems, while patient II phenotype is compatible with the 20p12 deletion since she manifests problems at the cardiac level, without significant dysmorphisms and an apparently normal psychomotor development.ConclusionsWhereas Alagille syndrome is a well characterized condition mainly caused by haploinsufficiency of JAG1 gene, with manifestations that can range from slight clinical findings to major symptoms in different domains, the 2q31.2q32.3 deletion syndrome is still being delineated. The occurrence of both imbalances in reported patient II would be expected to cause a more severe phenotype compared to the individual phenotype associated with each imbalance, which is not the case, since there are no manifestations due to the 2q32 deletion. This, together with the fact that patient I deleted region overlaps previously reported cases and patient II deletion is outside this common region, reinforces the existence of a critical region in 2q31.3q32.1, between 181 to 185 Mb, responsible for the clinical phenotype.

Do you know this syndrome? Dyspigmentation along the Blaschko lines caused by trisomy 7 mosaicism

Dyspigmentation along the Blaschko lines is strongly suggestive of a mosaic skin disorder. We report a 9-year-old male patient who presented with swirls and streaks of both hypo and hyperpigmentation involving the entire body. Additionally, he had hypertrichosis, musculoskeletal and minor neurodevelopment abnormalities but no intellectual disability. Cultured fibroblast displayed trisomy 7 mosaicism, which can explain this pigmentary phenotype. Widespread dyspigmentation associated with involvement of other organs should prompt systemic examination to detect additional anomalies and genetic evaluation should be considered, even with normal fetal karyotype.

Intellectual Disability, Unusual Facial Morphology and Hand Anomalies in Sibs

Here we report on a Portuguese family with three sisters who shared moderate intellectual disability, unusual facial morphology (short palpebral fissures; broad nasal tip; thin upper and lower vermillion; broad and pointed chin) and hand anomalies in two of them (short left third and fifth right metacarpals in one case; marked syndactyly between the third and fourth fingers in another). One of the sisters had microcephaly and short stature, and the other two were obese. Obesity and somewhat similar facial features were also present in the otherwise healthy mother. Despite the overlap with several known syndromes (Albright osteodystrophy; Filippi syndrome; Rubinstein–Taybi syndrome; microdeletion 2q37), we suggest this condition is previously unreported, and most likely displays an autosomal recessive pattern of inheritance.

Accuracy of Prenatal Diagnosis in Elective Termination of Pregnancy: 385 Cases from 2000 to 2007

Objective. To evaluate the quality of prenatal results in all cases of termination of pregnancy (TOP) due to fetal abnormalities in a tertiary prenatal diagnosis center. Material and Methods. Retrospective analysis of the 385 TOP performed on our department due to fetal abnormalities between January 1, 2000, and December 31, 2007. We compared all data for agreement between the ultrasound, genetic, and postmortem findings, regarding the abnormalities identified in the etiological diagnosis and its prognosis. Results. Chromosome abnormalities were the most common indication for TOP (39%), followed by abnormalities of CNS (20%), monogenic disorders (11%), sequences (9.6%), polimalformative syndromes (5.2%), and isolated congenital heart diseases (4%). Total agreement was 21%. Further abnormalities were identified in 79%. The data collected after TOP changed the etiologic diagnosis in 21% but the prognosis was changed in only one fetus. Discussion. This study corroborates the necessity of a multidisciplinary team in prenatal diagnosis centers. Their work remarkably improves the genetic counseling and represents an important aspect in quality control of the information given to a couple previously to a TOP.