Genome sequencing reveals underdiagnosis of primary ciliary dyskinesia in bronchiectasis.

BACKGROUND: Bronchiectasis can result from infectious, genetic, immunological and allergic causes. 60-80% of cases are idiopathic, but a well-recognised genetic cause is the motile ciliopathy, primary ciliary dyskinesia (PCD). Diagnosis of PCD has management implications including addressing comorbidities, implementing genetic and fertility counselling and future access to PCD-specific treatments. Diagnostic testing can be complex; however, PCD genetic testing is moving rapidly from research into clinical diagnostics and would confirm the cause of bronchiectasis. METHODS: This observational study used genetic data from severe bronchiectasis patients recruited to the UK 100,000 Genomes Project and patients referred for gene panel testing within a tertiary respiratory hospital. Patients referred for genetic testing due to clinical suspicion of PCD were excluded from both analyses. Data were accessed from the British Thoracic Society audit, to investigate whether motile ciliopathies are underdiagnosed in people with bronchiectasis in the UK. RESULTS: Pathogenic or likely pathogenic variants were identified in motile ciliopathy genes in 17 (12%) out of 142 individuals by whole-genome sequencing. Similarly, in a single centre with access to pathological diagnostic facilities, 5-10% of patients received a PCD diagnosis by gene panel, often linked to normal/inconclusive nasal nitric oxide and cilia functional test results. In 4898 audited patients with bronchiectasis, <2% were tested for PCD and <1% received genetic testing. CONCLUSIONS: PCD is underdiagnosed as a cause of bronchiectasis. Increased uptake of genetic testing may help to identify bronchiectasis due to motile ciliopathies and ensure appropriate management.

Chondrodysplasia with multiple dislocations: comprehensive study of a series of 30 cases.

The group of chondrodysplasia with multiple dislocations includes several entities, characterized by short stature, dislocation of large joints, hand and/or vertebral anomalies. Other features, such as epiphyseal or metaphyseal changes, cleft palate, intellectual disability are also often part of the phenotype. In addition, several conditions with overlapping features are related to this group and broaden the spectrum. The majority of these disorders have been linked to pathogenic variants in genes encoding proteins implicated in the synthesis or sulfation of proteoglycans (PG). In a series of 30 patients with multiple dislocations, we have performed exome sequencing and subsequent targeted analysis of 15 genes, implicated in chondrodysplasia with multiple dislocations, and related conditions. We have identified causative pathogenic variants in 60% of patients (18/30); when a clinical diagnosis was suspected, this was molecularly confirmed in 53% of cases. Forty percent of patients remain without molecular etiology. Pathogenic variants in genes implicated in PG synthesis are of major importance in chondrodysplasia with multiple dislocations and related conditions. The combination of hand features, growth failure severity, radiological aspects of long bones and of vertebrae allowed discrimination among the different conditions. We propose key diagnostic clues to the clinician.

A new explanation for recessive myotonia congenita: exon deletions and duplications in CLCN1.

OBJECTIVE: To assess whether exon deletions or duplications in CLCN1 are associated with recessive myotonia congenita (MC). METHODS: We performed detailed clinical and electrophysiologic characterization in 60 patients with phenotypes consistent with MC. DNA sequencing of CLCN1 followed by multiplex ligation-dependent probe amplification to screen for exon copy number variation was undertaken in all patients. RESULTS: Exon deletions or duplications in CLCN1 were identified in 6% of patients with MC. Half had heterozygous exonic rearrangements. The other 2 patients (50%), with severe disabling infantile onset myotonia, were identified with both a homozygous mutation, Pro744Thr, which functional electrophysiology studies suggested was nonpathogenic, and a triplication/homozygous duplication involving exons 8-14, suggesting an explanation for the severe phenotype. CONCLUSIONS: These data indicate that copy number variation in CLCN1 may be an important cause of recessive MC. Our observations suggest that it is important to check for exon deletions and duplications as part of the genetic analysis of patients with recessive MC, especially in patients in whom sequencing identifies no mutations or only a single recessive mutation. These results also indicate that additional, as yet unidentified, genetic mechanisms account for cases not currently explained by either CLCN1 point mutations or exonic deletions or duplications.

TRPV4 mutations and cytotoxic hypercalcemia in axonal Charcot-Marie-Tooth neuropathies.

OBJECTIVE: To improve understanding of TRPV4-associated axonal Charcot-Marie-Tooth (CMT) neuropathy phenotypes and their debated pathologic mechanism. METHODS: A total of 17 CMT2C phenotypic families with vocal cord and diaphragmatic involvement and 36 clinically undifferentiated CMT2 subjects underwent sequencing analysis of the coding region of TRPV4. Functional studies of mutant proteins were performed using transiently transfected cells for TRPV4 subcellular localization, basal and stimulated Ca(2+) channel analysis, and cell viability assay with or without channel blockade. RESULTS: Two TRPV4 mutations R232C and R316H from 17 CMT2C families were identified in the ankyrin repeat domains. The R316H is a novel de novo mutation found in a patient with CMT2C phenotype. The family with R232C mutation had individuals with and without vocal cord and diaphragm involvement. Both mutant TRPV4 proteins had normal subcellular localization in HEK293 and HeLa cells. Cells transfected with R232C and R316H displayed increased intracellular Ca(2+) levels and reversible cell death by the TRPV channel antagonist, ruthenium red. CONCLUSION: TRPV4 ankyrin domain alterations including a novel de novo mutation cause axonal CMT2. Individuals with the same mutation may have nondistinct CMT2 or have phenotypic CMT2C with vocal cord paresis. Reversible hypercalcemic gain-of-function of mutant TRPV4 instead of loss-of-function appears to be pathologically important. The reversibility of cell death by channel blockade provides an attractive area of investigation in consideration of treatable axonal degeneration.

Cleft lip with cleft palate, ankyloglossia, and hypodontia are associated with TBX22 mutations.

X-linked cleft palate and ankyloglossia (CPX) are caused by mutations in the TBX22 transcription factor. To investigate whether patients with ankyloglossia alone or in the presence of other craniofacial features including hypodontia or CLP might be caused by TBX22 mutations, we analyzed 45 Thai patients with isolated ankyloglossia, 2 unusual CPA families, and 282 non-syndromic Thai and UK patients with CLP. Five putative missense mutations were identified, including 3 located in the T-box binding domain (R120Q, R126W, and R151L) that affects DNA binding and/or transcriptional repression. The 2 novel C-terminal mutations, P389Q and S400Y, did not affect TBX22 activity. Mutations R120Q and P389Q were identified in patients with ankyloglossia only, while R126W and R151L were present in families that included CLP. Several individuals in these families were also found to have micro/hypodontia. This study has expanded the phenotypic spectrum of TBX22-related mutations to include dental anomalies and cleft lip.

Congenital glaucoma and brain stem atrophy as features of Aicardi-Goutières syndrome.

We report on three children from two families with Aicardi-Goutières syndrome. All three had congenital glaucoma. Additionally, neuroimaging demonstrated significant brain stem atrophy in the affected sib-pair. These features have not been previously described in Aicardi-Goutières syndrome and expand the phenotypic spectrum.

X-inactivation patterns in carriers of X-linked myotubular myopathy.

X-linked myotubular myopathy is a rare severe muscle disorder in affected male neonates. Most female carriers are free from symptoms. Skewed X inactivation has been proposed to be responsible for the affected phenotype seen in some carriers. We have compared the X inactivation patterns in blood DNA with the clinical phenotype in carriers of X-linked myotubular myopathy. The X-inactivation analysis was performed using HpaII predigestion of DNA followed by polymerase chain reaction of the highly polymorphic CAG repeat of the androgen receptor (AR) gene. The frequency of skewed X inactivation was similar in the X-linked myotubular myopathy carriers (22%) and in 235 controls (18%). Three overtly affected carriers had skewed X inactivation with the mutated X as the predominantly active X in at least two of them. Four females with mild symptoms had random X inactivation. The unaffected X-linked myotubular myopathy carriers had either skewed X inactivation in favour of expression from the normal X or random X-inactivation. Thus, there was a tendency for females with a more severe phenotype to have a skewed pattern of X inactivation, while females with an intermediate phenotype had a random pattern of X-inactivation.

Clinical and genetic heterogeneity in peroneal muscular atrophy associated with vocal cord weakness.

BACKGROUND: The peroneal muscular atrophy syndrome is the most common inherited disorder of the peripheral nervous system and has extensive clinical and genetic heterogeneity. Cranial nerve involvement is rare, though there are distinct peroneal muscular atrophy syndromes in which vocal cord paralysis is a characteristic feature. Among these dHMN-VII and HMSN-IIC are clinically similar but are differentiated by sensory involvement in HMSN-IIC. The gene for dHMN-VII, designated DHMNVP, has been localised to chromosome 2q14, but the location of the gene for HMSN-IIC is currently unknown. It has been suggested that dHMN-VII and HMSN II-C are allelic disorders. OBJECTIVE: To assess the contribution of the dHMN-VII predisposition gene to peroneal muscular atrophy syndromes associated with vocal cord weakness. METHODS: Linkage analysis of microsatellite markers at chromosome 2q14 was undertaken on two families, one affected by HMSN-IIC and a second manifesting vocal cord paralysis and sensorineural deafness in addition to distal muscular atrophy. RESULTS: Two-point LOD scores at chromosome 2q14 markers encompassing the DHMNVP gene were negative in both families. CONCLUSIONS: These results suggest that at least one further gene predisposing to distal muscular weakness in association with vocal cord paralysis is likely to exist, and that dHMN-VII and HMSN-IIC are unlikely to be allelic disorders. Analyses of further HMSN-IIC families are required to confirm this.

The KBG syndrome, characteristic dental findings: a case report.

Short stature and developmental delay may be observed in many genetic conditions and well-defined syndromes. A 7-year-old girl presented with the non-specific findings of subtle dysmorphism, short stature and developmental delay. Although a genetic syndrome was suspected, a definitive diagnosis was not made until the dental findings of KBG syndrome were recognised, namely grossly enlarged maxillary permanent central incisors and hypodontia.

Localization of the gene for distal hereditary motor neuronopathy VII (dHMN-VII) to chromosome 2q14.

Distal hereditary motor neuronopathy type VII (dHMN-VII) is an autosomal dominant disorder characterized by distal muscular atrophy and vocal cord paralysis. We performed a genomewide linkage search in a large Welsh pedigree with dHMN-VII and established linkage to chromosome 2q14. Analyses of a second family with dHMN-VII confirmed the location of the gene and provided evidence for a founder mutation segregating in both pedigrees. The maximum three-point LOD score in the combined pedigree was 7.49 at D2S274. Expansion of a polyalanine tract in Engrailed-1, a transcription factor strongly expressed in the spinal cord, was excluded as the cause of dHMN-VII.

Familial Prader-Willi syndrome: case report and a literature review.

Prader-Willi syndrome (PWS) is a neurobehavioural disorder arising through a number of different genetic mechanisms. All involve loss of paternal gene expression from chromosome 15q11q13. Although the majority of cases of PWS are sporadic, precise elucidation of the causative genetic mechanism is essential for accurate genetic counselling as the recurrence risk varies according to the mechanism involved. A pair of siblings affected by PWS is described. Neither demonstrates a microscopically visible deletion in 15q11q13 or maternal disomy. Methylation studies at D15S63 and at the SNRPN locus confirm the diagnosis of PWS. Molecular studies reveal biparental inheritance in both siblings with the exception of D15S128 and D15S63 where no paternal contribution is present indicating a deletion of the imprinting centre. Family studies indicate that the father of the siblings carries the deletion which, he has inherited from his mother. The recurrence risk for PWS in his offspring is 50%.

Mutational spectrum in the cardioauditory syndrome of Jervell and Lange-Nielsen.

Jervell and Lange-Nielsen syndrome (JLNS) is an autosomal recessive syndrome characterised by profound congenital sensorineural deafness and prolongation of the QT interval on the electrocardiogram, representing abnormal ventricular repolarisation. In a study of ten British and Norwegian families with JLNS, we have identified all of the mutations in the KCNQ1 gene, including two that are novel. Of the nine mutations identified in this group of 10 families, five are nonsense or frameshift mutations. Truncation of the protein proximal to the recently identified C-terminal assembly domain is expected to preclude assembly of KCNQ1 monomers into tetramers and explains the recessive inheritance of JLNS. However, study of a frameshift mutation, with a dominant effect phenotypically, suggests the presence of another assembly domain nearer to the N-terminus.

Chronic active destructive herpes simplex encephalitis with recovery of viral DNA 12 years after disease onset.

Acute herpes simplex encephalitis (HSE) carries significant morbidity and mortality even after early treatment with antiviral agents (7). As well as causing acute neurological disease, Herpes viruses are associated with relapsing--remitting (Varicella--Zoster, Epstein-Barr) and chronic (Rasmussen encephalitis) disease processes (1). A two-year-old girl developed acute HSE which was followed by a 10-year neurologic illness characterised by asymmetric spastic tetraparesis, pseudobulbar palsy, the opercular syndrome of Foix-Chavany-Marie (4) and seizures. The neurological signs remained static until the child died suddenly 12 years after disease onset. Neuropathologic examination demonstrated active chronic encephalitis. Herpes simplex virus (HSV) DNA was recovered from formalin-fixed paraffin-embedded brain tissue. This case provides additional evidence for the development of chronic neurological disease attributable to persistence of herpes simplex virus type 1.

Aicardi-Goutières syndrome: an expanding phenotype.

The Aicardi-Goutières syndrome (AGS) is an autosomal recessive progressive encephalopathy associated with basal ganglia calcification, white-matter abnormality, cerebro-spinal fluid (CSF) pleocytosis and elevated CSF interferon alpha (IFN alpha). Two brothers of consanguineous parents who presented in the first year with developmental delay are reported. The first boy is normocephalic with spastic diplegia and normal I.Q. Tests in the second year of life showed punctate calcification of the basal ganglia and subcortical white matter and CSF pleocytosis. At 9 years clinical and imaging features are unchanged and CSF including IFN alpha is normal. The second boy at 21 months has dystonic cerebral palsy, slight fall-off in head growth and cognitive delay. Imaging abnormalities are more severe than those in the brother, CSF examination reveals pleocytosis and marked increase in IFN alpha. Detailed metabolic and viral studies were negative in both cases. Although the clinical course is not progressive, it is suggested that the brothers have AGS and represent the mild end of the spectrum of the disorder. CSF examination (including IFN alpha), should be performed early in children with an apparently static encephalopathy and brain calcification, as typical abnormalities decrease or disappear with age.

Mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS) in a Donegal kindred--clinical features and molecular genetic analysis.

A 19 year old female with a background history of migraine, sensorineural deafness and recent personality change developed a parieto-occipital cerebral infarct. Investigations revealed altered lactate to pyruvate ratios, ragged red fibres in muscle and an A-G point mutation at position 3243 in mitochondrial DNA. Subsequent clinical and molecular genetic analysis of 14 family members in three generations identified 12 affected individuals, two of whom were asymptomatic. Maternal inheritance was confirmed. MEALS is an important but under recognised cause of stroke and seizures in the young. There is insufficient data available to determine if the treatment of asymptomatic individuals retards the onset or reduces the severity of stroke.