[show abstract][hide abstract] ABSTRACT: Genetic testing at a distance is commonplace where members of a family with a segregating germline mutation are geographically separated. For the most part, this challenge is addressed through the intervention of health professionals in taking and/or processing blood samples for subsequent couriering of DNA to a referral laboratory. In some circumstances, however, the collecting of pivotal clinical material may involve direct patient involvement. We describe such a situation where noninvasive saliva samples were provided by members of a family manifesting Von Hippel-Lindau (VHL) disease. The analysis identified a novel mutation in the VHL gene that was used to exclude other family members as being at risk of VHL disease.
Genetics research international. 01/2013; 2013:189196.
[show abstract][hide abstract] ABSTRACT: Molecular karyotyping using chromosome microarray analysis (CMA) detects more pathogenic chromosomal anomalies than classical karyotyping, making CMA likely to become a first tier test for prenatal diagnosis. Detecting copy number variants of uncertain clinical significance raises ethical considerations. We consider the risk of harm to a woman or her fetus following the detection of a copy number variant of uncertain significance, whether it is ethically justifiable to withhold any test result information from a woman, what constitutes an 'informed choice' when women are offered CMA in pregnancy and whether clinicians are morally responsible for 'unnecessary' termination of pregnancy. Although we are cognisant of the distress associated with uncertain prenatal results, we argue in favour of the autonomy of women and their right to information from genome-wide CMA in order to make informed choices about their pregnancies. We propose that information material to a woman's decision-making process, including uncertain information, should not be withheld, and that it would be paternalistic for clinicians to try to take responsibility for women's decisions to terminate pregnancies. Non-directive pre-test and post-test genetic counselling is central to the delivery of these ethical objectives.
[show abstract][hide abstract] ABSTRACT: The TRPV4 gene encodes a calcium-permeable ion-channel that is widely expressed, responds to many different stimuli and participates in an extraordinarily wide range of physiologic processes. Autosomal dominant brachyolmia, spondylometaphyseal dysplasia Kozlowski type (SMDK) and metatropic dysplasia (MD) are currently considered three distinct skeletal dysplasias with some shared clinical features, including short stature, platyspondyly, and progressive scoliosis. Recently, TRPV4 mutations have been found in patients diagnosed with these skeletal phenotypes.
We critically analysed the clinical and radiographic data on 26 subjects from 21 families, all of whom had a clinical diagnosis of one of the conditions described above: 15 with MD; 9 with SMDK; and 2 with brachyolmia. We sequenced TRPV4 and identified 9 different mutations in 22 patients, 4 previously described, and 5 novel. There were 4 mutation-negative cases: one with MD and one with SMDK, both displaying atypical clinical and radiographic features for these diagnoses; and two with brachyolmia, who had isolated spine changes and no metaphyseal involvement.
Our data suggest the TRPV4 skeletal dysplasias represent a continuum of severity with areas of phenotypic overlap, even within the same family. We propose that AD brachyolmia lies at the mildest end of this spectrum and, since all cases described with this diagnosis and TRPV4 mutations display metaphyseal changes, we suggest that it is not a distinct entity but represents the mildest phenotypic expression of SMDK.
[show abstract][hide abstract] ABSTRACT: Spinocerebellar ataxia type 20 (SCA20), first reported in 2004, is a slowly progressive dominantly inherited disorder so far reported in a single Anglo-Celtic family from Australia. It is characterized by dentate calcification from an early stage of the illness. Dysarthria without ataxia is the first symptom in the majority - an unusual feature amongst the SCAs. In addition to ataxia, examination often reveals spasmodic dysphonia and palatal tremor, but the syndrome is otherwise fairly pure. The responsible genetic abnormality has been tentatively identified as a 260-kb duplication in the pericentric region of chromosome 11, but confirmation will necessarily await description of further families.
Handbook of Clinical Neurology 01/2011; 103:567-73.
[show abstract][hide abstract] ABSTRACT: Spinocerebellar ataxia type 15 (SCA15), first described in 2001, is a slowly progressive, relatively pure dominantly inherited ataxia. Six pedigrees have been reported to date, in Anglo-Celtic and Japanese populations. Other than notably slow progression, its main distinguishing characteristic is tremor, often affecting the head, which is seen in about half of affecteds and which may be the presenting feature. Neuroradiology shows cerebellar atrophy, particularly affecting the anterior and dorsal vermis. SCA15 is due to various deletions of the inositol 1,4,5-triphosphate receptor 1 gene (ITPR1) on the distal short arm of chromosome 3. The potential of point mutations in ITPR1 to cause SCA15 is not yet confirmed. "SCA16" has now been shown to be due to an ITPR1 mutation, and has now been subsumed into SCA15.
Handbook of Clinical Neurology 01/2011; 103:561-5.
[show abstract][hide abstract] ABSTRACT: Periventricular heterotopia (PH) is a brain malformation characterised by heterotopic nodules of neurons lining the walls of the cerebral ventricles. Mutations in FLNA account for 20-24% of instances but a majority have no identifiable genetic aetiology. Often the co-occurrence of PH with a chromosomal anomaly is used to infer a new locus for a Mendelian form of PH. This study reports four PH patients with three different microdeletion syndromes, each characterised by high-resolution genomic microarray. In three patients the deletions at 1p36 and 22q11 are conventional in size, whilst a fourth child had a deletion at 7q11.23 that was larger in extent than is typically seen in Williams syndrome. Although some instances of PH associated with chromosomal deletions could be attributed to the unmasking of a recessive allele or be indicative of more prevalent subclinical migrational anomalies, the rarity of PH in these three microdeletion syndromes and the description of other non-recurrent chromosomal defects do suggest that PH may be a manifestation of multiple different forms of chromosomal imbalance. In many, but possibly not all, instances the co-occurrence of PH with a chromosomal deletion is not necessarily indicative of uncharacterised underlying monogenic loci for this particular neuronal migrational anomaly.
[show abstract][hide abstract] ABSTRACT: The identification of trisomy mosaicism in the prenatal setting is often shrouded with uncertainty for the genetic counsellor, and more importantly for the parents. The outcomes for these pregnancies may well be normal, but abnormalities and even in utero death are possibilities depending on the chromosomal abnormality and the degree of mosaicism. Advice to parents following the diagnosis of trisomy 16 mosaicism at chorionic villus sampling, with confirmation at subsequent amniocentesis, and in the setting of apparently normal fetal ultrasonography, is necessarily cautious. Malformations are seen in the majority of infants born following a diagnosis of mosaic trisomy 16 at amniocentesis, and intrauterine growth retardation, with postnatal catch-up, is the rule. We report here a case with a normal outcome by age 2.5 years and in fact with above-average language ability, and in whom trisomy mosaicism was confirmed postnatally.
Fetal Diagnosis and Therapy 01/2010; 28(2):117-8. · 1.90 Impact Factor
[show abstract][hide abstract] ABSTRACT: Spinocerebellar ataxia type 15 (SCA15) is a slowly progressive neurodegenerative disorder characterized by cerebellar ataxia. Mutation of the ITPR1 gene (inositol 1,4,5-triphosphate receptor, type 1) has been identified recently as the underlying cause, and in most cases the molecular defect is a multiexon deletion. To date, 5 different SCA15 families have been identified with ITPR1 gene deletion.
We have designed a synthetic, dual-color multiplex ligation-dependent probe amplification (MLPA) assay that measures copy number with high precision in selected exons across the entire length of ITPR1 and the proximal region of the neighboring gene, SUMF1 (sulfatase modifying factor 1). We screened 189 idiopathic ataxic patients with this MLPA assay.
We identified ITPR1 deletion of exons 1-10 in the previously reported AUS1 family (4 members) and deletion of exons 1-38 in a new family (2 members). In addition to the multiexon deletions, apparent single-exon deletions identified in 2 other patients were subsequently shown to be due to single-nucleotide changes at the ligation sites.
The frequency of ITPR1 deletions is 2.7% in known familial cases. This finding suggests that SCA15 is one of the "less common" SCAs. Although the deletions in the 5 families identified worldwide thus far have been of differing sizes, all share deletion of exons 1-10. This region may be important, both in terms of the underlying pathogenetic mechanism and as a pragmatic target for an accurate, robust, and cost-effective diagnostic analysis.
[show abstract][hide abstract] ABSTRACT: Spinocerebellar ataxia type 20 (SCA20) has been linked to chromosome 11q12, but the underlying genetic defect has yet to be identified. We applied single-nucleotide polymorphism genotyping to detect structural alterations in the genomic DNA of patients with SCA20. We found a 260 kb duplication within the previously linked SCA20 region, which was confirmed by quantitative polymerase chain reaction and fiber fluorescence in situ hybridization, the latter also showing its direct orientation. The duplication spans 10 known and 2 unknown genes, and is present in all affected individuals in the single reported SCA20 pedigree. While the mechanism whereby this duplication may be pathogenic remains to be established, we speculate that the critical gene within the duplicated segment may be DAGLA, the product of which is normally present at the base of Purkinje cell dendritic spines and contributes to the modulation of parallel fiber-Purkinje cell synapses.
Human Molecular Genetics 10/2008; 17(24):3847-53. · 7.69 Impact Factor
[show abstract][hide abstract] ABSTRACT: Dominant mutations in the three collagen VI genes cause Bethlem myopathy, a disorder characterized by proximal muscle weakness and commonly contractures of the fingers, wrists, and ankles. Although more than 20 different dominant mutations have been identified in Bethlem myopathy patients, the biosynthetic consequences of only a subset of these have been studied, and in many cases, the pathogenic mechanisms remain unknown.
We have screened fourteen Bethlem myopathy patients for collagen VI mutations and performed detailed analyses of collagen VI biosynthesis and intracellular and extracellular assembly.
Collagen VI abnormalities were identified in eight patients. One patient produced around half the normal amount of alpha1(VI) messenger RNA and reduced amounts of collagen VI protein. Two patients had a previously reported mutation causing skipping of COL6A1 exon 14, and three patients had novel mutations leading to in-frame deletions toward the N-terminal end of the triple-helical domain. These mutations have different and complex effects on collagen VI intracellular and extracellular assembly. Two patients had single amino acid substitutions in the A-domains of COL6A2 and COL6A3. Collagen VI intracellular and extracellular assembly was normal in one of these patients.
The key to dissecting the pathogenic mechanisms of collagen VI mutations lies in detailed analysis of collagen VI biosynthesis and assembly. The majority of mutations result in secretion and deposition of structurally abnormal collagen VI. However, one A-domain mutation had no detectable effect on assembly, suggesting that it acts by compromising collagen VI interactions in the extracellular matrix of muscle.
Annals of Neurology 11/2007; 62(4):390-405. · 11.19 Impact Factor
[show abstract][hide abstract] ABSTRACT: Nonsyndromic autosomal dominant sensorineural hearing loss (SNHL) at the DFNA10 locus was described in two families in 2001. Causative mutations that affect the EyaHR domain of the 'Eyes absent 4' (EYA4) protein were identified. We report on the clinical and genetic analyses of an Australian family with nonsyndromic SNHL. Screening of the EYA4 gene showed the novel polypyrimidine tract variation ca. 1,282-12T > A that introduces a new 3' splice acceptor site. This is the first report of a point mutation in EYA4 that is hypothesized to lead to aberrant pre-mRNA splicing and human disease. The DFNA10 family described is only the fourth to be identified. One individual presented with apparently the same phenotype as other affected members of the family. However, genotyping illustrated that he did not share the DFNA10 disease haplotype. Detailed clinical investigation showed differences in the onset and severity of his hearing loss and thus he is presumed to represent a phenocopy, perhaps resulting from long-term exposure to loud noise.
American Journal of Medical Genetics Part A 07/2007; 143A(14):1599-604. · 2.30 Impact Factor
[show abstract][hide abstract] ABSTRACT: We observed a severe autosomal recessive movement disorder in mice used within our laboratory. We pursued a series of experiments to define the genetic lesion underlying this disorder and to identify a cognate disease in humans with mutation at the same locus. Through linkage and sequence analysis we show here that this disorder is caused by a homozygous in-frame 18-bp deletion in Itpr1 (Itpr1(Delta18/Delta18)), encoding inositol 1,4,5-triphosphate receptor 1. A previously reported spontaneous Itpr1 mutation in mice causes a phenotype identical to that observed here. In both models in-frame deletion within Itpr1 leads to a decrease in the normally high level of Itpr1 expression in cerebellar Purkinje cells. Spinocerebellar ataxia 15 (SCA15), a human autosomal dominant disorder, maps to the genomic region containing ITPR1; however, to date no causal mutations had been identified. Because ataxia is a prominent feature in Itpr1 mutant mice, we performed a series of experiments to test the hypothesis that mutation at ITPR1 may be the cause of SCA15. We show here that heterozygous deletion of the 5' part of the ITPR1 gene, encompassing exons 1-10, 1-40, and 1-44 in three studied families, underlies SCA15 in humans.
[show abstract][hide abstract] ABSTRACT: Nonsyndromic autosomal-dominant, adult-onset sensorineural hearing loss resulting from DFNA17 was described in a single American kindred in 1997, and the causative gene was subsequently identified as MYH9.
The objective of this study was to report clinical and genetic analyses of an Australian family with nonsyndromic adult-onset sensorineural hearing loss.
The clinical presentation of the family was detailed and identification of the causative gene was conducted by SNP genotyping and direct sequencing.
Sequence analysis of the MYH9 gene revealed the same missense mutation as in the original DFNA17 family. We are not aware of a link between the two kindreds, making the present one only the second DFNA17 family to be reported.
One important point of clinical relevance is the excellent outcome with cochlear implants in the Australian family compared with a "poor" response in the American family. Thus, cochlear implants should be strongly considered for clinical management of patients with DFNA17 deafness.
The Laryngoscope 01/2007; 116(12):2211-5. · 1.98 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report a three-generation Caucasian family of Macedonian origin with dentatorubral-pallidoluysian atrophy (DRPLA), manifesting as very mild elderly onset, severe young adult onset, and severe childhood onset presentations in the three generations. The grandparental trinucleotide expansion size (52 repeats) is the smallest overtly pathogenic mutation yet reported. This 67-year-old man displayed only subtle neurological and cognitive deficits on formal examination and very slight signs on MRI. His son had developed a choreiform disorder at age 32 years, and by his 40s suffered severe dementia and motor decline. The grandson, the proband, presented as a teenager with progressive myoclonic epilepsy, dysarthria, ataxia, and cognitive decline, having manifesting learning difficulties from the age 5 years. Atrophin-1 expansion sizes of 52, 57, and 66 repeats were demonstrated in the three patients, respectively. Given an absence of any other indicative history in the family, we speculate that the mutation may have expanded from a 'high-end' normal allele to a pathogenic size at the grandfather's conception, or that one of his parents may have had a pathogenic mutation at the lowest end of the expanded range.
American Journal of Medical Genetics Part A 08/2005; 136(2):201-4. · 2.30 Impact Factor
[show abstract][hide abstract] ABSTRACT: To describe a fetal syndrome of abnormal brain development with intracranial calcification, identified in three successive pregnancies.
Clinical, imaging, and pathological descriptions, and pedigree assessment.
All three affected pregnancies were terminated, following imaging diagnosis of brain abnormality. The most complete fetal study, from the third of these pregnancies, showed widespread foci of brain calcification not associated with inflammation, with extensive necrosis and calcification of periventricular white matter, but with sparing of thalamus and basal ganglia. The corticospinal tracts were severely hypoplastic.
This condition appears to be a 'new' genetically determined, probably autosomal recessive disorder of severe early brain dysgenesis with focal calcification, resembling, but distinct from, certain other clinical genetic entities of which brain calcification is a part.
[show abstract][hide abstract] ABSTRACT: Prader-Willi syndrome (MIM #176270; PWS) is caused by lack of the paternally-derived copies, or their expression, of multiple genes in a 4 Mb region on chromosome 15q11.2. Known mechanisms include large deletions, maternal uniparental disomy or mutations involving the imprinting center. De novo balanced reciprocal translocations in 5 reported individuals had breakpoints clustering in SNRPN intron 2 or exon 20/intron 20. To further dissect the PWS phenotype and define the minimal critical region for PWS features, we have studied a 22 year old male with a milder PWS phenotype and a de novo translocation t(4;15)(q27;q11.2).
We used metaphase FISH to narrow the breakpoint region and molecular analyses to map the breakpoints on both chromosomes at the nucleotide level. The expression of genes on chromosome 15 on both sides of the breakpoint was determined by RT-PCR analyses.
Pertinent clinical features include neonatal hypotonia with feeding difficulties, hypogonadism, short stature, late-onset obesity, learning difficulties, abnormal social behavior and marked tolerance to pain, as well as sticky saliva and narcolepsy. Relative macrocephaly and facial features are not typical for PWS. The translocation breakpoints were identified within SNRPN intron 17 and intron 10 of a spliced non-coding transcript in band 4q27. LINE and SINE sequences at the exchange points may have contributed to the translocation event. By RT-PCR of lymphoblasts and fibroblasts, we find that upstream SNURF/SNRPN exons and snoRNAs HBII-437 and HBII-13 are expressed, but the downstream snoRNAs PWCR1/HBII-85 and HBII-438A/B snoRNAs are not.
As part of the PWCR1/HBII-85 snoRNA cluster is highly conserved between human and mice, while no copy of HBII-438 has been found in mouse, we conclude that PWCR1/HBII-85 snoRNAs is likely to play a major role in the PWS- phenotype.
BMC Medical Genetics 06/2005; 6:18. · 2.54 Impact Factor