Ruth McGowan

Heterogeneity of mutational mechanisms and modes of inheritance in auriculocondylar syndrome

Background Auriculocondylar syndrome (ACS) is a rare craniofacial disorder consisting of micrognathia, mandibular condyle hypoplasia and a specific malformation of the ear at the junction between the lobe and helix. Missense heterozygous mutations in the phospholipase C, β 4 (PLCB4) and guanine nucleotide binding protein (G protein), α inhibiting activity polypeptide 3 (GNAI3) genes have recently been identified in ACS patients by exome sequencing. These genes are predicted to function within the G protein-coupled endothelin receptor pathway during craniofacial development. Results We report eight additional cases ascribed to PLCB4 or GNAI3 gene lesions, comprising six heterozygous PLCB4 missense mutations, one heterozygous GNAI3 missense mutation and one homozygous PLCB4 intragenic deletion. Certain residues represent mutational hotspots; of the total of 11 ACS PLCB4 missense mutations now described, five disrupt Arg621 and two disrupt Asp360. The narrow distribution of mutations within protein space suggests that the mutations may result in dominantly interfering proteins, rather than haploinsufficiency. The consanguineous parents of the patient with a homozygous PLCB4 deletion each harboured the heterozygous deletion, but did not present the ACS phenotype, further suggesting that ACS is not caused by PLCB4 haploinsufficiency. In addition to ACS, the patient harbouring a homozygous deletion presented with central apnoea, a phenotype that has not been previously reported in ACS patients. Conclusions These findings indicate that ACS is not only genetically heterogeneous but also an autosomal dominant or recessive condition according to the nature of the PLCB4 gene lesion.

Bohring–Opitz (Oberklaid–Danks) syndrome: clinical study, review of the literature, and discussion of possible pathogenesis

Bohring–Opitz syndrome (BOS) is a rare congenital disorder of unknown etiology diagnosed on the basis of distinctive clinical features. We suggest diagnostic criteria for this condition, describe ten previously unreported patients, and update the natural history of four previously reported patients. This is the largest series reported to date, providing a unique opportunity to document the key clinical features and course through childhood. Investigations undertaken to try and elucidate the underlying pathogenesis of BOS using array comparative genomic hybridization and tandem mass spectrometry of cholesterol precursors did not show any pathogenic changes responsible.

Myhre and LAPS syndromes: clinical and molecular review of 32 patients

Myhre syndrome is characterized by short stature, brachydactyly, facial features, pseudomuscular hypertrophy, joint limitation and hearing loss. We identified SMAD4 mutations as the cause of Myhre syndrome. SMAD4 mutations have also been identified in laryngotracheal stenosis, arthropathy, prognathism and short stature syndrome (LAPS). This study aimed to review the features of Myhre and LAPS patients to define the clinical spectrum of SMAD4 mutations. We included 17 females and 15 males ranging in age from 8 to 48 years. Thirty were diagnosed with Myhre syndrome and two with LAPS. SMAD4 coding sequence was analyzed by Sanger sequencing. Clinical and radiological features were collected from a questionnaire completed by the referring physicians. All patients displayed a typical facial gestalt, thickened skin, joint limitation and muscular pseudohypertrophy. Growth retardation was common (68.7%) and was variable in severity (from −5.5 to −2 SD), as was mild-to-moderate intellectual deficiency (87.5%) with additional behavioral problems in 56.2% of the patients. Significant health concerns like obesity, arterial hypertension, bronchopulmonary insufficiency, laryngotracheal stenosis, pericarditis and early death occurred in four. Twenty-nine patients had a de novo heterozygous SMAD4 mutation, including both patients with LAPS. In 27 cases mutation affected Ile500 and in two cases Arg496. The three patients without SMAD4 mutations had typical findings of Myhre syndrome. Myhre–LAPS syndrome is a clinically homogenous condition with life threatening complications in the course of the disease. Our identification of SMAD4 mutations in 29/32 cases confirms that SMAD4 is the major gene responsible for Myhre syndrome.

DNA copy number variations are important in the complex genetic architecture of müllerian disorders

OBJECTIVE To clinically and genetically investigate women with müllerian disorders, including Mayer-Rokitanksy-Kuster-Hauser (MRKH) syndrome. DESIGN Two-year prospective clinical and laboratory study. SETTING Not applicable. PATIENT(S) Thirty-five women over 16 years of age with a müllerian disorder, including MRKH. INTERVENTION(S) Women were recruited from specialist gynecology clinics or identified from the Scottish Disorders of Sex Development Register (www.sdsd.scot.nhs.uk/index.html). Associated abnormalities were detected by clinical examination, imaging studies, and biochemical analyses. Chromosomal microduplications and microdeletions were detected by array comparative genomic hybridization (CGH) and validated by fluorescence in situ hydridization. MAIN OUTCOME MEASURE(S) Identification of associated congenital and biochemical abnormalities and identification of regions of genomic imbalance using array CGH. RESULT(S) Associated congenital anomalies were common, present in 25/35 (71%) of affected women, particularly renal and skeletal abnormalities, which were present in 15/35 (43%) and 17/35 (49%) women, respectively. Using array CGH, novel or recurrent regions of genomic imbalance were identified in 4/11 (36%) women with MRKH and in 5/24 (21%) women with other müllerian abnormalities. CONCLUSION(S) Additional congenital abnormalities and regions of genomic imbalance are common in women with müllerian disorders, including MRKH. Recurrent microdeletions and microduplications associated with MRKH implicate specific possibly causative genes. The investigation of women with müllerian disorders should be thorough, and array CGH should be considered, given the potential highly significant familial implications of a chromosomal abnormality.

Disorders of sex development: advances in genetic diagnosis and challenges in management

Disorders of sex development (DSD) are a group of rare conditions that usually present with atypical genitalia in the newborn period or as delayed puberty in an adolescent. Although a concern about the development of external genitalia may exist in one in 300 newborn infants, discrete genetic conditions that underlie DSD are generally rarely identified. It is likely that this diagnostic gap exists for a number of reasons and these include an inadequate knowl- edge of the pathogenesis and underlying mechanisms that lead to DSD, variation in assessment and in-depth phenotyping of these rare conditions, inadequate availability of quality accredited laboratories and, lastly, limited awareness of the value of a molecular genetic diagnosis for improving short-term and long-term care of the affected person.

Results of Duchenne muscular dystrophy family screening in practice: leaks rather than cascades?

McGowan R, Challoner BR, Ross S, Holloway S, Joss S, Wilcox D, Holden ST, Tolmie J, Longman C. Results of Duchenne muscular dystrophy family screening in practice: leaks rather than cascades?

The outcome of prenatal identification of sex chromosome abnormalities

Objective The outcome of a pregnancy following identification of a sex chromosome abnormality (SCA) is unclear. The aims of this study were to ascertain the prevalence of SCA detected prenatally in Scotland and to determine the outcomes for these cases. Design Following retrospective identification of all prenatal karyotypes performed in Scotland between 2000 and 2012, data linkage was performed to obtain information regarding maternal characteristics and pregnancy outcomes. Detailed outcome data were also collected for all affected offspring in the West of Scotland and Grampian regions within Scotland. Results Of the 28 145 pregnancies that had a karyotype over the study period, records were available for 27 152 (96%). Karyotype abnormalities were identified in 2139 (8%), with SCA being identified in 321(1%) tests. 45,X was identified as the commonest SCA in 135 pregnancies. Of 121 pregnancies with SCA in the West of Scotland and Grampian, 64 (53%), 52 (43%) and 5 (4%) led to a live birth, termination and intrauterine death, respectively. Of the 64 live births, 21 (33%) had a postnatal karyotype and 35 (54%) received specialist follow-up for the SCA that was identified prenatally. Conclusions Abnormalities of sex chromosomes are identified in approximately 1% of all pregnancies that undergo a prenatal karyotype. There is a need to review the prenatal as well as postnatal care of the affected mother and offspring.

ACTB Loss-of-Function Mutations Result in a Pleiotropic Developmental Disorder

ACTB encodes β-actin, an abundant cytoskeletal housekeeping protein. In humans, postulated gain-of-function missense mutations cause Baraitser-Winter syndrome (BRWS), characterized by intellectual disability, cortical malformations, coloboma, sensorineural deafness, and typical facial features. To date, the consequences of loss-of-function ACTB mutations have not been proven conclusively. We describe heterozygous ACTB deletions and nonsense and frameshift mutations in 33 individuals with developmental delay, apparent intellectual disability, increased frequency of internal organ malformations (including those of the heart and the renal tract), growth retardation, and a recognizable facial gestalt (interrupted wavy eyebrows, dense eyelashes, wide nose, wide mouth, and a prominent chin) that is distinct from characteristics of individuals with BRWS. Strikingly, this spectrum overlaps with that of several chromatin-remodeling developmental disorders. In wild-type mouse embryos, β-actin expression was prominent in the kidney, heart, and brain. ACTB mRNA expression levels in lymphoblastic lines and fibroblasts derived from affected individuals were decreased in comparison to those in control cells. Fibroblasts derived from an affected individual and ACTB siRNA knockdown in wild-type fibroblasts showed altered cell shape and migration, consistent with known roles of cytoplasmic β-actin. We also demonstrate that ACTB haploinsufficiency leads to reduced cell proliferation, altered expression of cell-cycle genes, and decreased amounts of nuclear, but not cytoplasmic, β-actin. In conclusion, we show that heterozygous loss-of-function ACTB mutations cause a distinct pleiotropic malformation syndrome with intellectual disability. Our biological studies suggest that a critically reduced amount of this protein alters cell shape, migration, proliferation, and gene expression to the detriment of brain, heart, and kidney development.

Pregnancy outcome following prenatal diagnosis of chromosomal anomaly: a record linkage study of 26,261 pregnancies

Previous studies have demonstrated the influence of changes in the age at which women give birth, and of developments in prenatal screening and diagnosis on the number of pregnancies diagnosed and terminated with chromosomal anomalies. However, we are unaware of any population studies examining pregnancy terminations after diagnosis of chromosomal anomalies that has included all aneuploidies and the influence of maternal factors. The aims of this study were to examine the association between results of prenatal tests and pregnancy termination, and the proportion of foetuses with and without chromosomal anomalies referred for invasive diagnostic tests over time. Diagnostic information of 26,261 prenatal invasive tests from all genetic service laboratories in Scotland from 2000 to 2011 was linked to Scottish Morbidity Records to obtain details on pregnancy outcome. Binary logistic regression was carried out to test the associations of year and type of diagnosis with pregnancy termination, while controlling for maternal age, neighbourhood deprivation and parity. There were 24,155 (92.0%) with no chromosomal anomalies, 1,483 (5.6%) aneuploidy diagnoses, and 623 (2.4%) diagnoses of anomaly that was not aneuploidy (including translocations and single chromosome deletions). In comparison with negative test results, pregnancies diagnosed with trisomy were most likely to be terminated (adjusted OR 437.40, 95% CI 348.19–549.46) followed by other aneuploid anomalies (adjusted OR 95.94, 95% CI 69.21–133.01). During the study period, fewer pregnancies that were diagnosed with aneuploidy were terminated, including trisomy diagnoses (adjusted OR 0.44, 95% CI 0.26–0.73). Older women were less likely to terminate (OR 0.35, 95% CI 0.28, 0.42), and parity was also an independent predictor of termination. In keeping with previous findings, while the number of invasive diagnostic tests declined, the proportion of abnormal results increased from 6.09% to 10.88%. Systematic advances in prenatal screening have improved detection rates for aneuploidy. This has been accompanied by a reduction in the rate of termination for aneuploidy. This may reflect societal changes with acceptance of greater diversity, but this is speculation, and further research would be needed to test this.

Novel Genetic Associations and Range of Phenotypes in Children with Disorders of Sex Development and Neurodevelopment: Insights from the Deciphering Developmental Disorders Study

A range of phenotypes that are associated with disorders of sex development (DSD) may also be encountered in patients with neurodevelopmental delay. In this study we have undertaken a collaborative retrospective review of anonymised phenotypic and genotypic data from the UK-wide Deciphering Developmental Disorders (DDD) study. Our objectives were to determine the frequency and range of DSD phenotypes observed in participants in the DDD study and to identify novel genetic associations. We found that of 7,439 DDD participants, 603 (8%) had at least one genital abnormality. In addition, we found that DSD occurs in 5% of patients with learning difficulties. Causative mutations were found in 13 developmental genes, of which, crucially, 6 had no previous reported association with DSD. Our findings indicate that recognition of these associations should not be overlooked in the management of patients with complex conditions and that exomic sequencing through projects like DDD increases diagnostic yield.