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Biomedical subjects

R J McKinlay Gardner

Publications and source records attributed to R J McKinlay Gardner.

At least 19 recordsLinked to original sources
PubMed2006

Cochlear implants for DFNA17 deafness.

BACKGROUND: 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. OBJECTIVE: The objective of this study was to report clinical and genetic analyses of an Australian family with nonsyndromic adult-onset sensorineural hearing loss. METHODS: The clinical presentation of the family was detailed and identification of the causative gene was conducted by SNP genotyping and direct sequencing. RESULTS: 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. CONCLUSIONS: 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.

Adolescent↗
PubMed2005

Dentatorubral-pallidoluysian atrophy in three generations, with clinical courses from nearly asymptomatic elderly to severe juvenile, in an Australian family of Macedonian descent.

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.

Adult↗
PubMed2005

Molecular breakpoint cloning and gene expression studies of a novel translocation t(4;15)(q27;q11.2) associated with Prader-Willi syndrome.

BACKGROUND: 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). METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Adult↗
PubMed2005

Severe fetal brain dysgenesis with focal calcification.

OBJECTIVE: To describe a fetal syndrome of abnormal brain development with intracranial calcification, identified in three successive pregnancies. METHODS: Clinical, imaging, and pathological descriptions, and pedigree assessment. RESULTS: 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. CONCLUSION: 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.

Abnormalities, Multiple↗
PubMed2005

Spinocerebellar ataxia type 15.

Spinocerebellar ataxia type 15 (SCA15) was first reported in 2001 on the basis of a single large Anglo-Celtic family from Australia, the locus mapping to chromosomal region 3p24.2-3pter. The characteristic clinical feature was of very slow progression, with two affected individuals remaining ambulant without aids after over 50 years of symptoms. Head and/or upper limb action tremor, and gaze-evoked horizontal nystagmus were seen in several persons. MRI brain scans showed predominant vermal atrophy, sparing the brainstem. In 2004, a Japanese pedigree was reported, which displayed very similar clinical features to the original SCA15 family, and which mapped to an overlapping candidate region. These two families might plausibly reflect a locus homogeneity, but for the present this remains an open question.

Cerebellum↗
PubMed2005

Spinocerebellar ataxia type 20.

Spinocerebellar ataxia type 20 (SCA20) was reported in 2004 in a single Australian Anglo-Celtic pedigree. The phenotype is distinctive, with palatal tremor, and hypermetric saccades, and early dentate (but not pallidal) calcification in the absence of abnormalities of calcium metabolism. Dysarthria, rather than gait ataxia, was the initial symptom in most, and was typically conjoined with dysphonia, clinically resembling adductor spasmodic dysphonia. The onset of these speech abnormalities was abrupt in some cases. MRI scanning showed mild to moderate pancerebellar atrophy with dentate calcification, with olivary pseudohypertrophy in some cases, in the absence of other brainstem or cerebral changes. Nerve conduction studies were normal. Progression appeared to be slow. SCA20 is probably rare, as despite the distinctive phenotype, only this one pedigree has been described. The locus mapped to the pericentromeric region of chromosome 11 with a LOD score of 4.47, and its candidate region overlaps that of SCA5. It seems probable that these two SCAs may be separate genetic entities, on the basis of their divergent clinical features, but formal proof awaits discovery of one or both responsible genes.

Adult↗
PubMed2004

Frequency of the ATM IVS10-6T-->G variant in Australian multiple-case breast cancer families.

BACKGROUND: Germline mutations in the genes BRCA1 and BRCA2 account for only a proportion of hereditary breast cancer, suggesting that additional genes contribute to hereditary breast cancer. Recently a heterozygous variant in the ataxia-telangiectasia mutated (ATM) gene, IVS10-6T-->G, was reported by an Australian multiple-case breast cancer family cohort study (the Kathleen Cuningham Foundation Consortium for Research into Familial Breast Cancer) to confer a substantial breast cancer risk. Although this variant can result in a truncated ATM product, its clinical significance as a high-penetrance breast cancer allele or its role as a low-penetrance risk-modifier is controversial. METHODS: We determined the frequency of ATM IVS10-6T-->G variants in a cohort of individuals affected by breast and/or ovarian cancer who underwent BRCA1 and BRCA2 genetic testing at four major Australian familial cancer clinics. RESULTS: Seven of 495 patients (1.4%) were heterozygous for the IVS10-6T-->G variant; the carrier rate in unselected Australian women with no family history of breast cancer is reported to be 6 of 725 (0.83%) (P = 0.4). Two of the seven probands also harboured a pathogenic BRCA1 mutation and one patient had a BRCA1 unclassified variant of uncertain significance. CONCLUSION: These findings indicate that the ATM IVS10-6T-->G variant does not seem to occur at a significantly higher frequency in affected individuals from high-risk families than in the general population. A role for this variant as a low-penetrance allele or as a modifying gene in association with other genes (such as BRCA1) remains possible. Routine testing for ATM IVS10-6T-->G is not warranted in mutation screening of affected individuals from high-risk families.

Adult↗
PubMed2004

Dominantly inherited ataxia and dysphonia with dentate calcification: spinocerebellar ataxia type 20.

We describe a pedigree of Anglo-Celtic origin with a phenotypically unique form of dominantly inherited spinocerebellar ataxia (SCA) in 14 personally examined affected members. A remarkable observation is dentate nucleus calcification, producing a low signal on MRI sequences. Unusually for an SCA, dysarthria is typically the initial manifestation. Mild pyramidal signs and hypermetric saccades are noted in some. Its distinguishing clinical features, each present in a majority of affected persons, are palatal tremor, and a form of dysphonia resembling spasmodic dysphonia. Repeat expansion detection failed to identify either CAG/CTG or ATTCT/AGAAT repeat expansions segregating with the disease in this family. The testable SCA mutations have been excluded. On linkage analysis, the locus maps to chromosome 11, which rules out all the remaining mapped SCAs except for SCA5. While locus homogeneity with SCA5 is not formally excluded, we consider it rather unlikely on phenotypic grounds, and propose that this condition may represent an addition to the group of neurogenetic disorders subsumed under the rubric SCA. The International Nomenclature Committee has made a provisional assignment of 'SCA20', although firm designation will have to await a definite molecular distinction from SCA5.

Adult↗
PubMed2003

Spinocerebellar ataxia type 15 (sca15) maps to 3p24.2-3pter: exclusion of the ITPR1 gene, the human orthologue of an ataxic mouse mutant.

We have studied a large Australian kindred with a dominantly inherited pure cerebellar ataxia, SCA15. The disease is characterised by a very slow rate of progression in some family members, and atrophy predominantly of the superior vermis, and to a lesser extent the cerebellar hemispheres. Repeat expansion detection failed to identify either a CAG/CTG or ATTCT/AGAAT repeat expansions segregating with the disease in this family. A genome-wide scan revealed significant evidence for linkage to the short arm of chromosome 3. The highest two-point LOD score was obtained with D3S3706 (Z = 3.4, theta = 0.0). Haplotype analysis identified recombinants that placed the SCA15 locus within an 11.6-cM region flanked by the markers D3S3630 and D3S1304. The mouse syntenic region contains two ataxic mutants, itpr1-/- and opt, affecting the inositol 1,4,5-triphosphate type 1 receptor, ITPR1 gene. ITPR1 is predominantly expressed in the cerebellar Purkinje cells. Mutation analysis from two representative affected family members excluded the coding region of the ITPR1 gene from being involved in the pathogenesis of SCA15. Thus, the itpr1-/- and opt ITPR1 mouse mutants, which each result in ataxia, are not allelic to the human SCA15 locus.

Animals↗
PubMed2002

Familial digital arthropathy-brachydactyly.

We report a large family with a previously undescribed, dominantly inherited condition comprising arthropathy of the hands and feet and progressive shortening of the middle and distal phalanges. We have designated the condition familial digital arthropathy-brachydactyly (FDAB). Onset of FDAB is in the first decade and the arthropathy is progressive, resulting in deformity and pain in adult life. The remainder of the skeleton is not affected. It is hypothesized from the radiological appearance of patients at different ages that FDAB might result from subchondral pathology primarily affecting the heads of the phalanges, metacarpals, and metatarsals, with the arthropathy and brachydactyly being secondary effects.

Arthritis↗
PubMed2002

Paternally inherited inactivating mutations of the GNAS1 gene in progressive osseous heteroplasia.

BACKGROUND: Progressive osseous heteroplasia (POH), an autosomal dominant disorder, is characterized by extensive dermal ossification during childhood, followed by disabling and widespread heterotopic ossification of skeletal muscle and deep connective tissue. Occasional reports of mild heterotopic ossification in Albright's hereditary osteodystrophy (AHO) and a recent report of two patients with AHO who had atypically extensive heterotopic ossification suggested a common genetic basis for the two disorders. AHO is caused by heterozygous inactivating mutations in the GNAS1 gene that result in decreased expression or function of the alpha subunit of the stimulatory G protein (Gsalpha) of adenylyl cyclase. METHODS: We tested the hypothesis that GNAS1 mutations cause POH, using the polymerase chain reaction to amplify GNAS1 exons and exon-intron boundaries in 18 patients with sporadic or familial POH. RESULTS: Heterozygous inactivating GNAS1 mutations were identified in 13 of the 18 probands with POH. The defective allele in POH is inherited exclusively from fathers, a result consistent with a model of imprinting for GNAS1. Direct evidence that the same mutation can cause either POH or AHO was observed within a single family, in which the phenotype correlated with the parental origin of the mutant allele. CONCLUSIONS: Paternally inherited inactivating GNAS1 mutations cause POH. This finding extends the range of phenotypes derived from haplo insufficiency of GNAS1, provides evidence that imprinting is a regulatory mechanism for GNAS1 expression, and suggests that Gsalpha is a critical negative regulator of osteogenic commitment in nonosseous connective tissues.

Base Sequence↗
PubMed2002

Isochromosome 5p mosaicism at prenatal diagnosis: observations and outcomes in six cases at chorionic villus sampling and one at amniocentesis.

We present six cases of 47,+i(5p)/46 mosaicism diagnosed at chorionic villus sampling (CVS), this being the first prospective series to be reported. The clinical indication in each was advanced maternal age. Further prenatal studies in four (amniocentesis, plus fetal blood sampling in one) did not show the isochromosome. In one case, subsequent amniocentesis showed 1/48 in situ colonies with the isochromosome, but fetal blood was karyotypically normal. These five pregnancies resulted in phenotypically normal livebirths; further normal follow-up reports (from age 4 months through 4 years) are noted in four of these. Analysis of placental tissue in one case confirmed the presence of the i(5p) mosaicism. In the remaining case, in which 100% of CVS cultured cells had the i(5p), the pregnancy was terminated. Fetal skin fibroblasts did not show the i(5p). Thus, in none of these six cases was true fetal mosaicism detected, nor an abnormal phenotype noted. We suggest that a 47,+i(5p)/46 karyotype, detected at CVS, may frequently reflect confined placental mosaicism. In addition, we report a case of the primary diagnosis of 47,+i(5p)/46 mosaicism at amniocentesis. The infant appeared normal at birth, but a brain malformation was subsequently identified.

Adult↗
PubMed2002

Chromosomal abnormalities and epilepsy: a review for clinicians and gene hunters.

PURPOSE: We analyzed databases on chromosomal anomalies and epilepsy to identify chromosomal regions where abnormalities are associated with clinically recognizable epilepsy syndromes. The expectation was that these regions could then be offered as targets in the search for epilepsy genes. METHODS: The cytogenetic program of the Oxford Medical Database, and the PubMed database were used to identify chromosomal aberrations associated with seizures and/or EEG abnormalities. The literature on selected small anomalies thus identified was reviewed from a clinical and electroencephalographic viewpoint, to classify the seizures and syndromes according to the current International League Against Epilepsy (ILAE) classification. RESULTS: There were 400 different chromosomal imbalances described with seizures or EEG abnormalities. Eight chromosomal disorders had a high association with epilepsy. These comprised: the Wolf-Hirschhorn (4p-) syndrome, Miller-Dieker syndrome (del 17p13.3), Angelman syndrome (del 15q11-q13), the inversion duplication 15 syndrome, terminal deletions of chromosome 1q and 1p, and ring chromosomes 14 and 20. Many other segments had a weaker association with seizures. The poor quality of description of the epileptology in many reports thwarted an attempt to make precise karyotype-phenotype correlations. CONCLUSIONS: We identified certain chromosomal regions where aberrations had an evident association with seizures, and these regions may be useful targets for gene hunters. New correlations with specific epilepsy syndromes were not revealed. Clinicians should continue to search for small chromosomal abnormalities associated with specific epilepsy syndromes that could provide important clues for finding epilepsy genes, and the epileptology should be rigorously characterized.

Chromosome Aberrations↗
PubMed2002

Identification of a haplosufficient 3.6-Mb region in human chromosome 11q14.3-->q21.

Cytogenetic deletions are almost always associated with phenotypic abnormality and are very rarely transmitted. We have located a hitherto undescribed, familial deletion involving the region 11q14.3-->q21 in five individuals in a three-generation kindred. Four of the deletion carriers show no phenotypic abnormality; the other, who is the proband, was investigated for short stature and poor academic progress. In view of the apparent innocuous nature of this genetic imbalance, the deletion was investigated in detail to determine its size (3.6 Mb) and location with reference to molecular markers and genetic content. The deleted region is described by a contig of 37 BACS including the flanking regions, which we have assembled. Several possible contributory factors are considered, which might explain the lack of clinical significance of this large deletion. It is notable that there are few genes in this region and none have known functions. All most likely have copies elsewhere in the genome and a number of other hypothetical genes appear to be members of certain gene families, i.e. none is unique. Part of the region (1 Mb) is also duplicated at the pericentromeric region 11p11. Given the very low proportion of the genome occupied by single copy genes and their uneven distribution, regions such as this, which appear to be functionally haplosufficient, may be more common than hitherto recognised.

Chromosome Banding↗
PubMed2001

Profuse familial adenomatous polyposis with an adenomatous polyposis coli exon 3 mutation.

The attenuated form of familial adenomatous polyposis coli (AAPC) is associated with mutations in the adenomatous polyposis coli (APC) gene which cluster in the 5' region of the gene. It has been proposed that a 'genotype-phenotype boundary' exists at codons 159-163, and mutations that are 5' of this boundary will produce AAPC. Herein we document a three-generation family with an exon 3 mutation well to the 5' side of the proposed boundary, in which two affected individuals have had, in their 40s, a profuse form of familial adenomatous polyposis coli. We conclude that the codon 159-163 'boundary' is indicative rather than definitive. These two patients also had postoperative intra-abdominal adhesions, severely so in one.

Adenomatous Polyposis Coli↗
PubMed2000

High frequency hearing loss correlated with mutations in the GJB2 gene.

Genetic hearing impairment affects approximately 1/2000 live births. Mutations in one gene, GJB2, coding for connexin 26 cause 10%-20% of all genetic sensorineural hearing loss. Mutation analysis in the GJB2 gene and audiology were performed on 106 families presenting with at least one child with congenital hearing loss. The families were recruited from a hospital-based multidisciplinary clinic, which functions to investigate the aetiology of sensorineural hearing loss in children and which serves an ethnically diverse population. In 74 families (80 children), the aetiology was consistent with non-syndromic recessive hearing loss. Six different connexin 26 mutations, including one novel mutation, were identified. We show that GJB2 mutations cause a range of phenotypes from mild to profound hearing impairment and that loss of hearing in the high frequency range (4000-8000 Hz) is a characteristic feature in children with molecularly diagnosed connexin 26 hearing impairment. We also demonstrate that this type of audiology and high frequency hearing loss is found in a similar-sized group of deaf children in whom a mutation could only be found in one of the connexin 26 alleles, suggesting connexin 26 involvement in the aetiology of hearing loss in these cases. In our study of the M34T mutation, only compound heterozygotes exhibited hearing loss, suggesting autosomal recessive inheritance.

Audiometry↗