Inherited Genetic Disease Group
|Dr Fierdoz Omar||Pathologist|
|Felicity Leisegang||Medical Scientist|
|Surita Meldau||Medical Scientist|
1. Epithelial sodium channel - in collaboration with Prof Brian Rayner
PhD project: Dr Erika Jones “The R563Q mutation of the epithelail sodium channel: prevalence and function.” - completed April 2010
The insights into the sodium epithelial channel b-chain has shown that the R563Q mutation may be a relatively common variant of the beta epithelial sodium channel in South African black people and may be a contributory factor to the high prevalence of hypertension in this population group.
MSc project: Raymond Moholisa “Analysis of a Variant in XPNPEP2 in Black African and Coloured South Africans Presenting with Angioedema Induced by Angiotensin I-converting Enzyme Inhibitors” - to be completed 2010
Angiotensin converting enzyme inhibitors (ACEi) are an important class of drugs widely used by more than 40 million patients worldwide. They are used as standard treatment for hypertension, congestive cardiac failure, renal disease and diabetes. Angioedema is an important adverse reaction associated with the use of ACEi, which has a higher prevalence in African Americans. In South Africa reports have suggested that ACEi angioedema is extremely common especially in the black and coloured populations, and may be life threatening or even fatal.
3. Complement 5 and Complement 6 deficient patients: Frequency of mutations in local population.
In collaboration with Dr Ann Orren, Cardiff University, UK, and Prof Paul Potter
Terminal complement components comprise the final five components of the complement cascade, C5 through to C9. All combine on target cell surfaces to produce the membrane attack complex (MAC) which is potentially lytic/harmful for bacteria, viruses and mammalian cells. MAC formation is not possible if any components are deficient. Complement deficiencies are rare genetic conditions associated with susceptibility to repeated Neisseria meningitidis infections. These deficiencies, particularly C6Q0, occur relatively frequently in the Western Cape. It is possible there are beneficial as well as detrimental consequences of complement deficiencies.
Previous studies identified four genetic defects responsible for C6Q0 in the Western Cape (2,3). We will examine the DNA from a group of South African control individuals (newborn cord bloods) and determine the population gene frequency of mutations leading to C6Q0.
We will investigate candidate proteins and genes which may explain why some patients are more susceptible to meningococcal infections than others.
Work on the implications of complement deficiency will continue as a few patients have chronic immunological problems. During the course of the study we may identify further individuals with terminal component deficiency (components C5 through to C9). If their gene defects are unknown they will be investigated.
4. Cystic fibrosis
Cystic fibrosis (CF) is a genetic disorder of the secretory glands, including the glands that make mucus and sweat. The hallmarks of CF are salty tasting skin, appetite but poor growth and poor weight gain, excess mucus production, and coughing/shortness of breath. Males can be infertile due to the condition congenital bilateral absence of the vas deferens. Often, symptoms of CF appear in infancy and childhood. Meconium ileus is a typical finding in newborn babies with CF. Although technically a rare disease, cystic fibrosis is ranked as one of the most widespread life-shortening genetic diseases.
The gold standard for CF diagnosis is the “sweat” test which if positive is followed by genetic analysis to enable extended family and antenatal testing. Unfortunately the sweat test is often inconclusive in babies and is only available in academic hospitals such as Red Cross Hospital for the Western Cape. Consequently doctors are becoming increasing reliant on genetic testing as the primary test especially for infants and patients living in rural areas.
Over 1,400 different mutations have been detected that can cause CF, however some mutations are more frequent than others. The most common mutation, ΔF508, accounts for two-thirds of CF cases worldwide in Caucasians. Commercial kits have been designed using allele specific primers to detect the frequent mutations in certain local populations. In South Africa we use a kit designed for people of French descent as it contains the most frequent mutations found in the local South African Caucasian population and the one known frequent mutation (3120+1G>A) that occurs in Africans. No specific kit is available for people of African descent for two reasons, firstly the spectrum of mutations in Africans is not fully known and secondly CF is much rarer in Africans than Caucasians making it of little commercial value to develop a specific kit.
We intend to define the spectrum of mutations found in the local African population and to design allele specific primers to detect these mutations in the local patients.
5. Development and Assessment of a Molecular Multiplex Screening Assay for detection of Glutaric Aciduria type 1 and Galactosaemia mutations in South Africa.
In collaboration with Dr G van der Watt
The scientific goal of this project is to apply and then adapt PCR based assays for three common point mutations. These are the A294T substitution in the glutaryl-CoA dehydrogenase gene, which causes glutaric aciduria type 1 (GA-1) in black South Africans, and the S135L and Q188R mutations in the galactos-1-phosphate uridyltransferase (GALT) gene, underlying galactosaemia in South African’s of Black, Mixed and European ancestries. Three standard and separate PCR assays have been develop and are in use in the NHLS/UCT laboratory at Groote Schuur Hospital. All three assays will be used to determine or confirm the carrier frequencies of these mutations in South African’s of black and mixed ancestries, in the first instance. The final goal is to assess, based on the data obtained, the feasibility of a newborn screening program or in an antenatal maternal risk profiling program to ultimately detect and prevent disease in affected neonates. To achieve this new cost effective methods need to be developed as current methods require considerable time and money. The validity of this approach stems from the finding that these mutations are responsible for >95% of all affected subjects with these two genetic conditions (Henderson et al : unpublished results RXH). One of the galactosaemia mutations chosen has a worryingly high carrier frequency in the black population, approx 1/60. We cannot comment on the carrier frequency in the mixed ancestry grouping as this has still to be determined. The GA-1 carrier frequency is unknown but likely to occur at a similar level as the galactosemia mutation. Current predictions are that homozygosity for these mutations, and hence disease, should be seen relatively commonly in South African newborns and represent a significant disease burden for two serious recessive diseases that are easily preventable by low cost interventions, provided affected individuals are detected early. South Africans of European ancestry will not be studied at this point as the prevalence rates for these two genetic conditions is low.
6. Feasibility of determining fetal RhD status and gender status in South African pregnant women using circulating fetal cell free DNA
The project aims to assess the feasibility of using circulating cell free fetal DNA analysis in maternal blood to determine
- Fetal RhD status in pregnant women who are RhD negative
- Fetal gender status in patients at risk for congenital adrenal hyperplasia or X-linked diseases.
- Assess the sensitivity and specificity of these tests for these diagnoses in the different gestational age groups in the local population.
- Rayner BL, Owen EP, King JA, Soule SG, Vreede H, Opie LH, Marais D, Davidson JS.
A new mutation, R563Q, of the beta subunit of the epithelia sodium channel associated with low-renin, low-aldosterone hypertension.
J Hypertension 2003 Vol 21 No 5.
- Heckmann JM, Lambson EM, Little F, Owen EP.
Thiopurine methyltransferase (TPMT) heterozygosity and enzyme activity as predictive tests for the development of azathioprine-related adverse events.
J Neurol Sci. 2005 Apr 15;231(1-2):71-80.
- Human BA, Owen EP, Compagno LJ, Harley EH.
Testing morphologically based phylogenetic theories within the cartilaginous fishes with molecular data, with special reference to the catshark family (Chondrichthyes; Scyliorhinidae) and the interrelationships within them.
Mol Phylogenet Evol. 2006 May;39(2):384-91. Epub 2005 Nov 15.
- Dhanjal MK, Owen EP, Anthony JA, Davidson JS, Rayner BL.
Association of pre-eclampsia with the R563Q mutation of the beta-subunit of the epithelial sodium channel.
BJOG. 2006 May;113(5):595-8
- Swarts L, Leisegang F, Owen EP, Henderson HE.
An OTC deficiency 'phenocopy' in association with Klinefelter syndrome.
J Inherit Metab Dis. 2007 Feb;30(1):101.
- Heckmann JM, Owen EP, Little F.
Myasthenia gravis in South Africans: Racial differences in clinical manifestations.
Neuromuscul Disord. 2007 Aug 24;
- Fukao T, Kursula P, Owen EP, Kondo N
Identification and characterization of a temperature-sensitive R268H mutation in the human succinyl-CoA:3-ketoacid CoA transferase (SCOT) gene.
Mol Genet Metab. 2007 Nov;92(3):216-221.
- Williams EL, Acquaviva C, Amoroso A, Chevalier F, Coulter Mackie M, Monico C, Giachino D, Owen EP, Robbiano A, Salido E, Waterham H, Rumsby G.
Primary hyperoxaluria type 1: Update and additional mutation analysis of the AGXT gene.
Human Mutation vol 30, no 6, 910-917, 2009
- Van der Watt G, Owen EP, Berman P, Meldau S, Watermeyer N, Olpin SE, Manning NJ, Baumgarten I, Leisegang F, Henderson H.
Glutaric aciduria type 1 in South Africa—high incidence of glutaryl-CoA2 dehydrogenase deficiency in black South Africans.
Molecular Genetics and Metabolism 2010 Oct-Nov;101(2-3):178-82.
- Jones ESW, Owen EP, Davidson JS, van der Merwe L, Rayner Bl.
The R563Q Mutation of the Epithelial sodium channel beta subunit is associated with Hypertension.
CardioVascular Journal of Africa 2010 in press
- Owen EP, Heckmann J, Riordan GMT.
Mitochondrial encephalopathies: Experience at Groote Schuur Hospital and Red Cross War Memorial Childrens Hospital. In preparation