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Publications (4)17.52 Total impact

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    ABSTRACT: We report on the fifth case, and oldest reported patient, of an individual affected with mosaic tetrasomy 5p resulting from an isochromosome 5p [i(5)(p10)] marker chromosome. A syndrome of mosaic tetrasomy 5p is defined, and includes the following features seen in the reported cases: developmental delay, seizures, ventriculomegaly (other brain anomalies), small stature/growth delay and mosaic pigmentary skin changes. Other findings include various dysmorphic facial features as well as hand and foot anomalies. This syndrome is likely more common than suggested in the literature, as the clinical presentation can be variable, and the chromosome anomaly is unlikely to be found on routine karyotype of peripheral blood lymphocytes. The i(5)(p10) marker chromosome is found only as a mosaic anomaly, with levels ranging from 0% to 10% in cultured lymphocytes to 12-85% in cultured skin fibroblasts. Microarray analysis performed on unstimulated lymphocytes from the patient in this report did not detect any evidence of the chromosome abnormality, indicating that this methodology may not be useful as a diagnostic tool in this disorder. Diagnosis of the mosaic tetrasomy 5p syndrome will rely on good clinical assessment, and appropriate cytogenetic studies, including analysis of skin fibroblasts. A child with unexplained developmental delay, seizures, hypotonia, and ventriculomegaly with or without dysmorphic features should be assessed carefully for pigmentary changes of the skin. If a diagnosis of mosaic 5p tetrasomy is suspected, karyotype of cultured fibroblasts in addition to routine cytogenetic analysis, to look for this marker chromosome is warranted.
    American Journal of Medical Genetics Part A 02/2012; 158A(2):406-11. · 2.30 Impact Factor
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    ABSTRACT: Primary microcephaly is a rare condition in which brain size is substantially diminished without other syndromic abnormalities. Seven autosomal loci have been genetically mapped, and the underlying causal genes have been identified for MCPH1, MCPH3, MCPH5, MCPH6, and MCPH7 but not for MCPH2 or MCPH4. The known genes play roles in mitosis and cell division. We ascertained three families from an Eastern Canadian subpopulation, each with one microcephalic child. Homozygosity analysis in two families using genome-wide dense SNP genotyping supported linkage to the published MCPH4 locus on chromosome 15q21.1. Sequencing of coding exons of candidate genes in the interval identified a nonconservative amino acid change in a highly conserved residue of the centrosomal protein CEP152. The affected children in these two families were both homozygous for this missense variant. The third affected child was compound heterozygous for the missense mutation plus a second, premature-termination mutation truncating a third of the protein and preventing its localization to centrosomes in transfected cells. CEP152 is the putative mammalian ortholog of Drosphila asterless, mutations in which affect mitosis in the fly. Published data from zebrafish are also consistent with a role of CEP152 in centrosome function. By RT-PCR, CEP152 is expressed in the embryonic mouse brain, similar to other MCPH genes. Like some other MCPH genes, CEP152 shows signatures of positive selection in the human lineage. CEP152 is a strong candidate for the causal gene underlying MCPH4 and may be an important gene in the evolution of human brain size.
    The American Journal of Human Genetics 07/2010; 87(1):40-51. · 11.20 Impact Factor
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    ABSTRACT: von Hippel-Lindau (VHL) disease is an autosomal dominant condition characterized by the development of benign and malignant tumours, including cases of renal cell carcinoma (RCC). Early detection of RCC through routine surveillance can lead to decreased morbidity and mortality. Data on the number of patients in Nova Scotia (NS) who have VHL disease, disease manifestations and the frequency and mode of the surveillance have not previously been collected or reported. This project was designed to obtain that information. The number and management of patients with VHL disease was determined by multiple sources: the Maritime Medical Genetics Service, patient charts, and pathology, radiology and laboratory data. The actual surveillance being performed was compared with that recommended in the literature. Twenty-one patients from 11 families in NS were identified. Manifestations included cases of RCC (31.6%), central nervous system (CNS) hemangioblastoma (73.7%), retinal hemangioma (47.4%), renal cyst (47.4%) and pheochromocytoma (10.5%). Of the 6 patients with RCC, 4 had bilateral tumours, 2 required kidney transplants and 1 developed metastatic disease. Routine surveillance was being done for the CNS in 62.5% of patients, retina in 47.4%, abdomen in 43.8% and urine catecholamines in only 10.5%. Only 1 of the 6 patients who developed RCC was undergoing routine abdominal imaging. Surveillance investigations were ordered by a number of different specialists. Patients with VHL disease in NS have a number of manifestations associated with their disease, including RCC, in a similar frequency to that reported in the literature. The surveillance of these patients is suboptimal in frequency and coordination. von Hippel-Lindau disease is a complex condition that requires a coordinated approach to care to ensure proper surveillance and treatment. Our study highlights current deficiencies and offers an enormous opportunity for improvement.
    Canadian Urological Association journal = Journal de l'Association des urologues du Canada 03/2009; 3(1):32-6. · 1.66 Impact Factor
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    ABSTRACT: We report a child with polycythemia vera (PV). This patient demonstrates the acquired somatic JAK2 V617F mutation and also has neurofibromatosis type I (NF1). NF1, while not previously associated with PV, is associated with another childhood MPD, juvenile myelomonocytic leukemia (JMML). Thus we examined a number of genetic abnormalities identified in JMML patients, but found no association in this case. Neurofibromin sequencing failed to identify a causative mutation. An unknown genetic abnormality resulting in NF1 may have predisposed this young child to acquiring the common JAK2 mutation.
    Pediatric Blood & Cancer 08/2008; 51(5):689-91. · 2.35 Impact Factor