[Show abstract][Hide abstract] ABSTRACT: Infantile hypertrophic pyloric stenosis (IHPS) is the most common inherited form of gastrointestinal obstruction in infancy
with a striking male preponderance. Infants present with vomiting due to gastric outlet obstruction caused by hypertrophy
of the smooth muscle of the pylorus. Two loci specific to extended pedigrees displaying autosomal dominant inheritance have
been identified. A genome scan identified loci on chromosomes 11q14–q22 and Xq23–q24 which are predicted to be responsible
for a subset of smaller families with IHPS demonstrating non-Mendelian inheritance. The two linked chromosomal regions both
harbour functional candidate genes which are members of the canonical transient receptor potential (TRPC) family of ion channels.
Both TRPC5 (Xq23–q24) and TRPC6 (11q14–q22) have a potential role in smooth muscle control and hypertrophy. Here, we report suggestive evidence for a third
locus on chromosome 3q12–q25 (Z
max=2.7, p<0.004), a region which harbours a third TRPC gene, TRPC1. Fine mapping of all three genes using a tagSNP approach and re-sequencing identified a SNP in the promoter region of TRPC6 and a missense variant in exon 4 of TRPC6 which may be putative causal variants.
Human Genetics 12/2009; 126(6):819-831. DOI:10.1007/s00439-009-0735-5 · 4.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Childhood absence epilepsy (CAE) is an idiopathic generalised epilepsy (IGE) characterised by typical absence seizures manifested by transitory loss of awareness with 2.5–4 Hz spike-wave complexes on ictal EEG. A genetic component to the aetiology is well recognised but the mechanism of inheritance and the genes involved are yet to be fully established.
A genome wide single nucleotide polymorphism (SNP)-based high density linkage scan was carried out using 41 nuclear pedigrees with at least two affected members. Multipoint parametric and non-parametric linkage analyses were performed using MERLIN 1.1.1 and a susceptibility locus was identified on chromosome 3p23-p14 (Zmean = 3.9, p < 0.0001; HLOD = 3.3, α = 0.7). The linked region harbours the functional candidate genes TRAK1 and CACNA2D2. Fine-mapping using a tagSNP approach demonstrated disease association with variants in TRAK1.
Epilepsy research 10/2009; 87(2-3):247-55. DOI:10.1016/j.eplepsyres.2009.09.010 · 2.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Primary ciliary dyskinesia (PCD) is a genetically heterogeneous inherited disorder arising from dysmotility of motile cilia and sperm. This is associated with a variety of ultrastructural defects of the cilia and sperm axoneme that affect movement, leading to clinical consequences on respiratory-tract mucociliary clearance and lung function, fertility, and left-right body-axis determination. We performed whole-genome SNP-based linkage analysis in seven consanguineous families with PCD and central-microtubular-pair abnormalities. This identified two loci, in two families with intermittent absence of the central-pair structure (chromosome 6p21.1, Zmax 6.7) and in five families with complete absence of the central pair (chromosome 6q22.1, Zmax 7.0). Mutations were subsequently identified in two positional candidate genes, RSPH9 on chromosome 6p21.1 and RSPH4A on chromosome 6q22.1. Haplotype analysis identified a common ancestral founder effect RSPH4A mutation present in UK-Pakistani pedigrees. Both RSPH9 and RSPH4A encode protein components of the axonemal radial spoke head. In situ hybridization of murine Rsph9 shows gene expression restricted to regions containing motile cilia. Investigation of the effect of knockdown or mutations of RSPH9 orthologs in zebrafish and Chlamydomonas indicate that radial spoke head proteins are important in maintaining normal movement in motile, "9+2"-structure cilia and flagella. This effect is rescued by reintroduction of gene expression for restoration of a normal beat pattern in zebrafish. Disturbance in function of these genes was not associated with defects in left-right axis determination in humans or zebrafish.
The American Journal of Human Genetics 03/2009; 84(2):197-209. DOI:10.1016/j.ajhg.2009.01.011 · 10.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Following a 15-week attachment in paediatrics and child health, general practice and dermatology medical students in their second clinical year at this medical school undertake a high-stakes assessment including an objective structured clinical examination (OSCE). There were 2 hypotheses. Firstly, groups of similar stations map to competency domains identifiable by factor analysis. Secondly, poor performance in individual domains is compensated for by achieving the required standard of performance across the whole assessment.
A total of 647 medical students were assessed by an OSCE during 5 individual examination sittings (diets) over 2 years. Ten scoring stations in the OSCE were analysed and confirmatory factor analysis performed comparing a 1-factor model (where all the stations are discrete entities related to one underlying domain) with a 3-factor model (where the stations load onto 3 domains from a previously reported exploratory factor analysis).
The 3-factor model yielded a significantly better fit to the data (chi(2 )=( )15.3, P < 0.01). Assessing the compensation data of 1 diet, 29 of 127 students failed in 1 or more domains described, whereas only 5 failed if compensation was allowed across all domains.
Confirmatory factor analysis showed a significant fit of the data to previously described competency domains for a high-stakes undergraduate OSCE. Compensation within but not between competency domains would provide a more robust standard, improve validity, and substantially reduce the pass rate.
Medical Education 06/2008; 42(6):600-6. DOI:10.1111/j.1365-2923.2008.03021.x · 3.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Infantile hypertrophic pyloric stenosis (IHPS) is the most common inherited form of gastrointestinal obstruction in infancy. The disease is considered a paradigm for the sex-modified model of multifactorial inheritance and affects males four times more frequently than females. However, extended pedigrees consistent with autosomal dominant inheritance have been documented. We have analysed data from an extended IHPS family including eight affected individuals (five males and three females) and mapped the disease locus to chromosome 16q24 (LOD score=3.7) through an SNP-based genome wide scan. Fourteen additional multiplex pedigrees did not show evidence of linkage to this region, indicating locus heterogeneity.
European Journal of HumanGenetics 06/2008; 16(9):1151-4. DOI:10.1038/ejhg.2008.86 · 4.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Infantile hypertrophic pyloric stenosis (IHPS) has an incidence of 1-8 per 1000 live births and is inherited as a complex sex-modified multifactorial trait with a striking male preponderance. Syndromic and monogenic forms exist, and two loci have been identified. Infants present with vomiting due to gastric-outlet obstruction caused by hypertrophy of the smooth muscle of the pylorus. A genome-wide SNP-based high-density linkage scan was carried out on 81 IHPS pedigrees. Nonparametric and parametric linkage analysis identified loci on chromosomes 11q14-q22 (Z(max) = 3.9, p < 0.0001; HLOD(max) = 3.4, alpha = 0.34) and Xq23 (Z(max) = 4.3, p < 0.00001; HLOD(max) = 4.8, alpha = 0.56). The two linked chromosomal regions each harbor functional candidate genes that are members of the canonical transient receptor potential (TRPC) family of ion channels and have a potential role in smooth-muscle control and hypertrophy.
The American Journal of Human Genetics 03/2008; 82(3):756-62. DOI:10.1016/j.ajhg.2007.12.023 · 10.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Paroxysmal extreme pain disorder (PEPD), previously known as familial rectal pain (FRP, or OMIM 167400), is an inherited condition characterized by paroxysms of rectal, ocular, or submandibular pain with flushing. A genome-wide linkage search followed by mutational analysis of the candidate gene SCN9A, which encodes hNa(v)1.7, identified eight missense mutations in 11 families and 2 sporadic cases. Functional analysis in vitro of three of these mutant Na(v)1.7 channels revealed a reduction in fast inactivation, leading to persistent sodium current. Other mutations in SCN9A associated with more negative activation thresholds are known to cause primary erythermalgia (PE). Carbamazepine, a drug that is effective in PEPD, but not PE, showed selective block of persistent current associated with PEPD mutants, but did not affect the negative activation threshold of a PE mutant. PEPD and PE are allelic variants with distinct underlying biophysical mechanisms and represent a separate class of peripheral neuronal sodium channelopathy.
[Show abstract][Hide abstract] ABSTRACT: Idiopathic generalized epilepsy (IGE) accounts for approximately 20% of all epilepsies and affects about 0.2% of the general population. The etiology of IGE is genetically determined, but the complex pattern of inheritance suggests an involvement of a large number of susceptibility genes. The objective of the present study was to explore the genetic architecture of common IGE syndromes and to dissect out susceptibility loci predisposing to absence or myoclonic seizures.
Genome-wide linkage scans were performed in 126 IGE-multiplex families of European origin ascertained through a proband with idiopathic absence epilepsy or juvenile myoclonic epilepsy. Each family had at least two siblings affected by IGE. To search for seizure type-related susceptibility loci, linkage analyses were carried out in family subgroups segregating either typical absence seizures or myoclonic and generalized tonic-clonic seizures on awakening.
Nonparametric linkage scans revealed evidence for complex and heterogeneous genetic architectures involving linkage signals at 5q34, 6p12, 11q13, 13q22-q31, and 19q13. The signal patterns differed in their composition, depending on the predominant seizure type in the families.
Our results are consistent with heterogeneous configurations of susceptibility loci associated with different IGE subtypes. Genetic determinants on 11q13 and 13q22-q31 seem to predispose preferentially to absence seizures, whereas loci on 5q34, 6p12, and 19q13 confer susceptibility to myoclonic and generalized tonic-clonic seizures on awakening.
[Show abstract][Hide abstract] ABSTRACT: CACNA1H was evaluated in a resource of Caucasian European patients with childhood absence epilepsy by linkage analysis and typing of sequence variants previously identified in Chinese patients. Linkage analysis of 44 pedigrees provided no evidence for a locus in the CACNA1H region and none of the Chinese variants were found in 220 unrelated patients.
Epilepsy Research 06/2006; 69(2):177-81. DOI:10.1016/j.eplepsyres.2006.01.009 · 2.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, we elucidate the roles of the winged-helix transcription factor Foxa2 in ventral CNS development in zebrafish. Through cloning of monorail (mol), which we find encodes the transcription factor Foxa2, and phenotypic analysis of mol-/- embryos, we show that floorplate is induced in the absence of Foxa2 function but fails to further differentiate. In mol-/- mutants, expression of Foxa and Hh family genes is not maintained in floorplate cells and lateral expansion of the floorplate fails to occur. Our results suggest that this is due to defects both in the regulation of Hh activity in medial floorplate cells as well as cell-autonomous requirements for Foxa2 in the prospective laterally positioned floorplate cells themselves. Foxa2 is also required for induction and/or patterning of several distinct cell types in the ventral CNS. Serotonergic neurones of the raphenucleus and the trochlear motor nucleus are absent in mol-/- embryos, and oculomotor and facial motoneurones ectopically occupy ventral CNS midline positions in the midbrain and hindbrain. There is also a severe reduction of prospective oligodendrocytes in the midbrain and hindbrain. Finally, in the absence of Foxa2, at least two likely Hh pathway target genes are ectopically expressed in more dorsal regions of the midbrain and hindbrain ventricular neuroepithelium, raising the possibility that Foxa2 activity may normally be required to limit the range of action of secreted Hh proteins.
Development 03/2005; 132(4):645-58. DOI:10.1242/dev.01611 · 6.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Primary ciliary dyskinesia is an autosomal recessive disorder characterised by recurrent sinopulmonary infections, bronchiectasis, and subfertility, due to dysfunction of the cilia. Fifty percent of patients with primary ciliary dyskinesia have defects of laterality (situs inversus) and this association is known as Kartagener syndrome. Primary ciliary dyskinesia has an estimated incidence of 1 in 20 000 live births.
To identify loci for this genetically heterogeneous condition, genome wide linkage scans and subsequent fine mapping were performed in two different isolated populations with distinct ciliary ultrastructural defects, from the Faroe Islands and the Druze community in northern Israel.
A locus was mapped in seven families from the Faroe Islands to a 2.8 cM interval on chromosome 16p12.1-12.2, with a maximum lod score of 3.15, obtained using GENEHUNTER. A locus was mapped in three out of four Druze families from the Golan region of Israel to a 17 cM region on chromosome 15q13.1-15.1, with a maximum hlod score of 3.2 at (proportion of linked families) = 0.7, using GENEHUNTER.
This study provides further evidence of the genetic heterogeneity underlying primary ciliary dyskinesia and has established a framework to facilitate isolation of two genes for primary ciliary dyskinesia. Determining the molecular basis of primary ciliary dyskinesia will provide insight into the genetic control of cilia assembly and function and the pathway which determines the vertebrate left right axis.
Journal of Medical Genetics 04/2004; 41(3):233-40. · 6.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The neuronal ceroid lipofuscinoses (NCLs) are a group of autosomal recessive neurodegenerative diseases of childhood. CLN6, the gene mutated in variant late infantile NCL (vLINCL), was recently cloned. We report the identification of eight further mutations in CLN6 making a total of 18 reported mutations. These mutations include missense, nonsense, small deletions or insertions, and two splice-site mutations. Ten mutations affect single amino acids, all of which are conserved across vertebrate species. Minor differences in the pattern of disease symptom evolution can be identified. One patient with a more protracted disease progression was a compound heterozygote for a missense mutation and an unidentified mutation. Fifteen CLN6 mutations occur in one or two families only, and families from the same country do not all share the same mutation. Unlike NCLs caused by mutations in CLN1, CLN3, CLN5, and CLN8, there is no major founder mutation in CLN6. However, one mutation (E72X) is significantly more common in patients from Costa Rica than two other mutations present in that same population. In addition, a 1-bp insertion (c.316insC) is associated with families from Pakistan and I154del may be common in Portugal. A group of Roma Gypsy families from the Czech Republic share two disease-associated haplotypes, one of which is also present in a Pakistani family, consistent with the proposed migration of the Roma from the Indian subcontinent 1,000 years ago. All mutations are recorded in the NCL Mutation Database together with their country of origin for use in the development of rapid screening assays to confirm diagnosis and to facilitate carrier testing appropriate to a population.
Human Mutation 07/2003; 22(1):35-42. DOI:10.1002/humu.10227 · 5.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A recent genome-wide scan revealed a major susceptibility locus for idiopathic generalized epilepsies (IGEs) in the chromosomal region 8p12 in 32 IGE families without members with juvenile myoclonic epilepsy (JME). This study explored the presence of an IGE locus in the chromosomal region 8p12.
Our study included 176 multiplex families of probands with common IGE syndromes. Parametric and nonparametric multipoint linkage analyses were carried out between the IGE trait and six microsatellite polymorphisms encompassing the putative susceptibility locus. To explore the associated phenotype-genotype relation, two distinct subgroups of families were selected by the presence (n = 64) or absence (n = 112) of a family member with JME. To adjust the phenotypic spectrum toward adolescent-onset IGEs, a third subgroup of 28 families without JME was chosen through an IGE proband with seizure onset at age 10-20 years.
Parametric and nonparametric multipoint linkage analyses provided no evidence for linkage between IGE and markers encompassing the putative IGE locus in the chromosomal region 8p12. Furthermore, we found no hint of linkage along the candidate region in any of the three family subgroups.
We failed to provide evidence for a major IGE locus in the chromosomal region 8p12. On the contrary, these parametric linkage results provide strong evidence against linkage across the candidate region under a broad range of genetic models. If there is a susceptibility locus for IGE in the chromosomal region 8p12, then the size of the effect or the proportion of linked families is too small to detect linkage in the investigated family sample.
[Show abstract][Hide abstract] ABSTRACT: A recent genome-wide scan revealed suggestive evidence for two susceptibility loci for idiopathic generalized epilepsy (IGE) in the chromosomal regions 5p15 and 5q14-q22 in families with typical absence seizures. The present replication study tested the validity of the tentative IGE loci on chromosome 5. Our study included 99 multiplex families in which at least one family member had typical absence seizures. Parametric and non-parametric multipoint linkage analyses were carried out between the IGE trait and 23 microsatellite polymorphisms covering the entire region of chromosome 5. Multipoint parametric heterogeneity lod scores < -2 were obtained along chromosome 5 when a proportion of linked families greater than 50% was assumed under recessive inheritance and > 60% under dominant inheritance. Furthermore, non-parametric multipoint linkage analyses revealed no hint of linkage throughout the candidate region (P > 0.05). Accordingly, we failed to support previous evidence for common IGE loci on chromosome 5. If there is a susceptibility locus for IGE on chromosome 5 then the size of the effect or the proportion of linked families is too small to detect linkage in the investigated family sample.
Epilepsy Research 10/2002; 51(1-2):23-9. DOI:10.1016/S0920-1211(02)00097-9 · 2.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A recent genome-wide scan showed strong evidence for a major locus for common syndromes of idiopathic generalized epilepsy (IGE) at the marker D18S474 on chromosome 18q21.1 (LOD score 4.5/5.2 multipoint/two-point). The present replication study tested the presence of an IGE locus in the chromosomal region 18q21.1. Our linkage study included 130 multiplex families of probands with common IGE syndromes. Eleven microsatellite polymorphisms encompassing a candidate region of 30 cM on either side of the marker D18S474 were genotyped. The two-point homogeneity LOD score for D18S474 showed strong evidence against linkage at the original linkage peak (Z = -18.86 at theta(m = f) = 0.05), assuming a recessive mode of inheritance with 50% penetrance. Multipoint parametric heterogeneity LOD scores < -2 were obtained along the candidate region when proportions of linked families greater than 35% were assumed under recessive inheritance. Furthermore, non-parametric multipoint linkage analyses showed no hint of linkage throughout the candidate region (P > 0.19). Accordingly, we failed to support evidence for a major IGE locus in the chromosomal region 18p11-18q23. If there is a susceptibility locus for IGE in this region then the size of the effect or the proportion of linked families is too small to detect linkage in the investigated family sample.
American Journal of Medical Genetics 08/2002; 114(6):673-8. DOI:10.1002/ajmg.10645 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Multisystem pseudohypoaldosteronism (PHA), is a syn- drome of unresponsiveness to aldosterone with autosomal recessive inheritance. Previously we showed that muta- tions in the epithelial sodium channel (ENaC) -, -, and -subunits are responsible for PHA. In this study we exam- ined four independent probands with multisystem PHA, three of whom were born to consanguineous parents. In our search for mutations we also determined the complete cod- ing sequences of each of the three genes encoding -, -, and -subunits in individuals representing different ethnic groups. Our analyses revealed the following homozygous mutations in three probands: 1) insertion o faTi nexon 8 of the ENaC gene that causes a frameshift error at Tyr447 and leads to a premature stop codon at K459 in a Pakistani patient; 2) R508stop mutation in exon 11 of the ENaC gene in an Indian patient; and 3) a splice site mutation in intron 12 of the ENaC gene (1669 1g 3a) in a Scottish patient. The parents were heterozygous for the latter two mutations. The second mutation was previously observed in an Iranian Jewish patient. Our sequencing of the -, -, and -coding sequences revealed some sequence variants, some of which may represent single nucleotide polymorphisms. The -sub- unit protein sequence was completely conserved in the six subjects examined. The homozygous mutations identified in the and ENaC genes should result in reduced or abol- ished ENaC activity in PHA patients, explaining the disease symptoms. (J Clin Endocrinol Metab 87: 3344 -3350, 2002)
[Show abstract][Hide abstract] ABSTRACT: Multisystem pseudohypoaldosteronism (PHA), is a syndrome of unresponsiveness to aldosterone with autosomal recessive inheritance. Previously we showed that mutations in the epithelial sodium channel (ENaC) alpha-, beta-, and gamma-subunits are responsible for PHA. In this study we examined four independent probands with multisystem PHA, three of whom were born to consanguineous parents. In our search for mutations we also determined the complete coding sequences of each of the three genes encoding alpha-, beta-, and gamma-subunits in individuals representing different ethnic groups. Our analyses revealed the following homozygous mutations in three probands: 1) insertion of a T in exon 8 of the alpha ENaC gene that causes a frameshift error at Tyr(447) and leads to a premature stop codon at K459 in a Pakistani patient; 2) R508stop mutation in exon 11 of the alpha ENaC gene in an Indian patient; and 3) a splice site mutation in intron 12 of the beta ENaC gene (1669 + 1 g-->a) in a Scottish patient. The parents were heterozygous for the latter two mutations. The second mutation was previously observed in an Iranian Jewish patient. Our sequencing of the alpha-, beta-, and gamma-coding sequences revealed some sequence variants, some of which may represent single nucleotide polymorphisms. The gamma-subunit protein sequence was completely conserved in the six subjects examined. The homozygous mutations identified in the alpha and beta ENaC genes should result in reduced or abolished ENaC activity in PHA patients, explaining the disease symptoms.
[Show abstract][Hide abstract] ABSTRACT: Genetics continues to advance at an accelerating pace. The completion of the human genome draft sequence is a milestone in human biology, and represents the foundation stone for a revolution in our understanding of the biology of man. Annotation of the genome, that is elucidating the function of all the genes, represents a major challenge for the future. Over 1000 Mendelian disease genes have now been identified and recent discoveries concerning the role of ion channels in human epilepsies are reviewed. The focus is now shifting towards the analysis of ‘complex’ traits using new information on human genetic variation manifested as single-nucleotide polymorphisms. Identification of a susceptibility locus for Crohn's disease,N0D2 , represents a first step in this direction.
Current Paediatrics 06/2002; 12(3):238-243. DOI:10.1054/cupe.2001.0291
[Show abstract][Hide abstract] ABSTRACT: A previous study of 34 nuclear pedigrees segregating juvenile myoclonic epilepsy (JME) gave significant evidence of linkage with heterogeneity to marker loci on chromosome 15q13-14 close to the candidate gene CHRNA7 (Hum. Mol. Genet. 6 (1997) 1329). The aim of this work was to further evaluate the putative aetiological role of CHRNA7 in JME within the 34 families originally described, and to assess the contribution of this locus to a broader phenotype of idiopathic generalised epilepsy (IGE). Multipoint linkage analysis and intrafamilial association studies were performed with microsatellite markers that encompass both CHRNA7 and its partial duplication (CHRFAM7A). A maximum HLOD of 3.45 [alpha=0.58; (Zall=2.88, P=0.0008)] was observed 8 cM distal to D15S1360, a CHRNA7 intragenic marker. Significant exclusion lod scores were obtained across the region in 12 mixed phenotype JME/IGE families. Mutation screening of the CHRNA7 gene (and consequently exons 5-10 of CHRFAM7A) and its putative promoter sequence identified a total of 13 sequence variants across 23 of 34 JME-affected families. Two variants (c.1354G>A and c.1466C>T) are predicted to result in amino acid changes and one (IVS9+5G>A) is predicted to result in aberrant transcript splicing. However, none of the variants alone appeared either necessary or sufficient to cause JME in the families in which they occurred. In conclusion, linkage analyses continue to support the existence of a locus on chromosome 15q13-14 that confers susceptibility to JME but not to a broader IGE phenotype. Causal sequence variants in the positional candidate CHRNA7 have not been identified but the presence of multiple segmental duplications in this region raises the possibility of undetected disease-causing genomic rearrangements.
Epilepsy Research 04/2002; 49(2):157-72. DOI:10.1016/S0920-1211(02)00027-X · 2.02 Impact Factor