Jill Clayton-Smith

Recurrent rearrangements of chromosome 1q21.1 and variable pediatric phenotypes

BACKGROUND Duplications and deletions in the human genome can cause disease or predispose persons to disease. Advances in technologies to detect these changes allow for the routine identification of submicroscopic imbalances in large numbers of patients. METHODS We tested for the presence of microdeletions and microduplications at a specific region of chromosome 1q21.1 in two groups of patients with unexplained mental retardation, autism, or congenital anomalies and in unaffected persons. RESULTS We identified 25 persons with a recurrent 1.35-Mb deletion within 1q21.1 from screening 5218 patients. The microdeletions had arisen de novo in eight patients, were inherited from a mildly affected parent in three patients, were inherited from an apparently unaffected parent in six patients, and were of unknown inheritance in eight patients. The deletion was absent in a series of 4737 control persons (P=1.1x10(-7)). We found considerable variability in the level of phenotypic expression of the microdeletion; phenotypes included mild-to-moderate mental retardation, microcephaly, cardiac abnormalities, and cataracts. The reciprocal duplication was enriched in nine children with mental retardation or autism spectrum disorder and other variable features (P=0.02). We identified three deletions and three duplications of the 1q21.1 region in an independent sample of 788 patients with mental retardation and congenital anomalies. CONCLUSIONS We have identified recurrent molecular lesions that elude syndromic classification and whose disease manifestations must be considered in a broader context of development as opposed to being assigned to a specific disease. Clinical diagnosis in patients with these lesions may be most readily achieved on the basis of genotype rather than phenotype.

Cognitive function at 3 years of age after fetal exposure to antiepileptic drugs

BACKGROUND Fetal exposure of animals to antiepileptic drugs at doses lower than those required to produce congenital malformations can produce cognitive and behavioral abnormalities, but cognitive effects of fetal exposure of humans to antiepileptic drugs are uncertain. METHODS Between 1999 and 2004, we enrolled pregnant women with epilepsy who were taking a single antiepileptic agent (carbamazepine, lamotrigine, phenytoin, or valproate) in a prospective, observational, multicenter study in the United States and the United Kingdom. The primary analysis is a comparison of neurodevelopmental outcomes at the age of 6 years after exposure to different antiepileptic drugs in utero. This report focuses on a planned interim analysis of cognitive outcomes in 309 children at 3 years of age. RESULTS At 3 years of age, children who had been exposed to valproate in utero had significantly lower IQ scores than those who had been exposed to other antiepileptic drugs. After adjustment for maternal IQ, maternal age, antiepileptic-drug dose, gestational age at birth, and maternal preconception use of folate, the mean IQ was 101 for children exposed to lamotrigine, 99 for those exposed to phenytoin, 98 for those exposed to carbamazepine, and 92 for those exposed to valproate. On average, children exposed to valproate had an IQ score 9 points lower than the score of those exposed to lamotrigine (95% confidence interval [CI], 3.1 to 14.6; P=0.009), 7 points lower than the score of those exposed to phenytoin (95% CI, 0.2 to 14.0; P=0.04), and 6 points lower than the score of those exposed to carbamazepine (95% CI, 0.6 to 12.0; P=0.04). The association between valproate use and IQ was dose dependent. Childrens IQs were significantly related to maternal IQs among children exposed to carbamazepine, lamotrigine, or phenytoin but not among those exposed to valproate. CONCLUSIONS In utero exposure to valproate, as compared with other commonly used antiepileptic drugs, is associated with an increased risk of impaired cognitive function at 3 years of age. This finding supports a recommendation that valproate not be used as a first-choice drug in women of childbearing potential.

The longer term outcome of children born to mothers with epilepsy

Objectives: To determine the prevalence of cognitive delay and possible associated dysmorphic features in children exposed to antiepileptic drugs (AEDs) in utero. Design: Retrospective study of children born to mothers with epilepsy. Setting: Regional epilepsy clinics in Liverpool and Manchester, UK. Participants: Children aged between 6 months and 16 years born to mothers with epilepsy. Main outcome measures: Structured interviews, hospital records, clinical examination, and psychometric tests (Wechsler) were used to assess exposure and intelligence quotient (IQ). Blinded assessment of photographs was used to score children with characteristic dysmorphic features. Results: A total of 249 children aged 6 and over were studied: 41 were exposed to sodium valproate, 52 to carbamazepine, 21 to phenytoin, 49 to polytherapy, and 80 were unexposed. Mean verbal IQ was significantly lower in the valproate group compared to unexposed and other monotherapy groups. Multiple regression analysis showed that both valproate exposure and frequent tonic-clonic seizures in pregnancy were significantly associated with a lower verbal IQ despite adjusting for other confounding factors. There was a significant negative correlation between dysmorphic features and verbal IQ in children exposed to valproate. Conclusions: This study identifies valproate as a drug carrying potential risks for developmental delay and cognitive impairment and is the first to suggest that frequent tonic-clonic seizures have a similar effect. Our results need to be interpreted with caution given their retrospective nature. Women with epilepsy need careful counselling about individual risk benefit of AED treatment before pregnancy.

Large, rare chromosomal deletions associated with severe early-onset obesity

Obesity is a highly heritable and genetically heterogeneous disorder. Here we investigated the contribution of copy number variation to obesity in 300 Caucasian patients with severe early-onset obesity, 143 of whom also had developmental delay. Large (>500 kilobases), rare (<1%) deletions were significantly enriched in patients compared to 7,366 controls (P < 0.001). We identified several rare copy number variants that were recurrent in patients but absent or at much lower prevalence in controls. We identified five patients with overlapping deletions on chromosome 16p11.2 that were found in 2 out of 7,366 controls (P < 5 × 10-5). In three patients the deletion co-segregated with severe obesity. Two patients harboured a larger de novo 16p11.2 deletion, extending through a 593-kilobase region previously associated with autism and mental retardation; both of these patients had mild developmental delay in addition to severe obesity. In an independent sample of 1,062 patients with severe obesity alone, the smaller 16p11.2 deletion was found in an additional two patients. All 16p11.2 deletions encompass several genes but include SH2B1, which is known to be involved in leptin and insulin signalling. Deletion carriers exhibited hyperphagia and severe insulin resistance disproportionate for the degree of obesity. We show that copy number variation contributes significantly to the genetic architecture of human obesity.

Angelman syndrome 2005: updated consensus for diagnostic criteria.

In 1995, a consensus statement was published for the purpose of summarizing the salient clinical features of Angelman syndrome (AS) to assist the clinician in making a timely and accurate diagnosis. Considering the scientific advances made in the last 10 years, it is necessary now to review the validity of the original consensus criteria. As in the original consensus project, the methodology used for this review was to convene a group of scientists and clinicians, with experience in AS, to develop a concise consensus statement, supported by scientific publications where appropriate. It is hoped that this revised consensus document will facilitate further clinical study of individuals with proven AS, and assist in the evaluation of those who appear to have clinical features of AS but have normal laboratory diagnostic testing.

Fetal antiepileptic drug exposure and cognitive outcomes at age 6 years (NEAD study): a prospective observational study

BACKGROUND Many women of childbearing potential take antiepileptic drugs, but the cognitive effects of fetal exposure are uncertain. We aimed to assess effects of commonly used antiepileptic drugs on cognitive outcomes in children up to 6 years of age. METHODS In this prospective, observational, assessor-masked, multicentre study, we enrolled pregnant women with epilepsy on antiepileptic drug monotherapy (carbamazepine, lamotrigine, phenytoin, or valproate) between October, 1999, and February, 2004, at 25 epilepsy centres in the UK and the USA. Our primary outcome was intelligence quotient (IQ) at 6 years of age (age-6 IQ) in all children, assessed with linear regression adjusted for maternal IQ, antiepileptic drug type, standardised dose, gestational birth age, and use of periconceptional folate. We also assessed multiple cognitive domains and compared findings with outcomes at younger ages. This study is registered with ClinicalTrials.gov, number NCT00021866. FINDINGS We included 305 mothers and 311 children (six twin pairs) in the primary analysis. 224 children completed 6 years of follow-up (6-year-completer sample). Multivariate analysis of all children showed that age-6 IQ was lower after exposure to valproate (mean 97, 95% CI 94-101) than to carbamazepine (105, 102-108; p=0·0015), lamotrigine (108, 105-110; p=0·0003), or phenytoin (108, 104-112; p=0·0006). Children exposed to valproate did poorly on measures of verbal and memory abilities compared with those exposed to the other antiepileptic drugs and on non-verbal and executive functions compared with lamotrigine (but not carbamazepine or phenytoin). High doses of valproate were negatively associated with IQ (r=-0·56, p<0·0001), verbal ability (r=-0·40, p=0·0045), non-verbal ability (r=-0·42, p=0·0028), memory (r=-0·30, p=0·0434), and executive function (r=-0·42, p=0·0004), but other antiepileptic drugs were not. Age-6 IQ correlated with IQs at younger ages, and IQ improved with age for infants exposed to any antiepileptic drug. Compared with a normative sample (173 [93%] of 187 children), right-handedness was less frequent in children in our study overall (185 [86%] of 215; p=0·0404) and in the lamotrigine (59 [83%] of 71; p=0·0287) and valproate (38 [79%] of 40; p=0·0089) groups. Verbal abilities were worse than non-verbal abilities in children in our study overall and in the lamotrigine and valproate groups. Mean IQs were higher in children exposed to periconceptional folate (108, 95% CI 106-111) than they were in unexposed children (101, 98-104; p=0·0009). INTERPRETATION Fetal valproate exposure has dose-dependent associations with reduced cognitive abilities across a range of domains at 6 years of age. Reduced right-handedness and verbal (vs non-verbal) abilities might be attributable to changes in cerebral lateralisation induced by exposure to antiepileptic drugs. The positive association of periconceptional folate with IQ is consistent with other recent studies.

Angelman syndrome phenotype associated with mutations in MECP2, a gene encoding a methyl CpG binding protein.

Angelman syndrome (AS) is a neurodevelopmental disorder characterised by severe mental retardation, absent speech, ataxia, sociable affect, and dysmorphic facial features. Eighty five percent of patients with AS have an identifiable genetic abnormality of chromosome 15q11-13. Mutations within the X linkedMECP2 gene have been identified in patients with Rett syndrome (RTT), a neurodevelopmental disorder which affects females almost exclusively and which shares phenotypic overlap with AS. RTT is usually associated with normal development in infancy followed by loss of acquired skills and evolution of characteristic hand wringing movements and episodes of hyperventilation. A panel of 25 female and 22 male patients with a clinical diagnosis of AS and no molecular abnormality of 15q11-13 were screened for MECP2 mutations and these were identified in four females and one male. Following the diagnosis, it was possible to elicit a history of regression in three of these patients, who by then were showing features suggestive of Rett syndrome. In the remaining two subjects the clinical phenotype was still considered to be Angelman-like. These findings illustrate the phenotypic overlap between the two conditions and suggest that screening forMECP2 mutations should be considered in AS patients without a demonstrable molecular or cytogenetic abnormality of 15q11-13. Since MECP2 mutations almost always occur de novo, their identification will substantially affect genetic counselling for the families concerned.

Haploinsufficiency of TCF4 causes syndromal mental retardation with intermittent hyperventilation (Pitt-Hopkins syndrome).

Pitt-Hopkins syndrome is a rarely reported syndrome of so-far-unknown etiology characterized by mental retardation, wide mouth, and intermittent hyperventilation. By molecular karyotyping with GeneChip Human Mapping 100K SNP arrays, we detected a 1.2-Mb deletion on 18q21.2 in one patient. Sequencing of the TCF4 transcription factor gene, which is contained in the deletion region, in 30 patients with significant phenotypic overlap revealed heterozygous stop, splice, and missense mutations in five further patients with severe mental retardation and remarkable facial resemblance. Thus, we establish the Pitt-Hopkins syndrome as a distinct but probably heterogeneous entity caused by autosomal dominant de novo mutations in TCF4. Because of its phenotypic overlap, Pitt-Hopkins syndrome evolves as an important differential diagnosis to Angelman and Rett syndromes. Both null and missense mutations impaired the interaction of TCF4 with ASCL1 from the PHOX-RET pathway in transactivating an E box-containing reporter construct; therefore, hyperventilation and Hirschsprung disease in patients with Pitt-Hopkins syndrome might be explained by altered development of noradrenergic derivatives.

Human osteoclast-poor osteopetrosis with hypogammaglobulinemia due to TNFRSF11A (RANK) mutations.

Autosomal-Recessive Osteopetrosis (ARO) comprises a heterogeneous group of bone diseases for which mutations in five genes are known as causative. Most ARO are classified as osteoclast-rich, but recently a subset of osteoclast-poor ARO has been recognized as due to a defect in TNFSF11 (also called RANKL or TRANCE, coding for the RANKL protein), a master gene driving osteoclast differentiation along the RANKL-RANK axis. RANKL and RANK (coded for by the TNFRSF11A gene) also play a role in the immune system, which raises the possibility that defects in this pathway might cause osteopetrosis with immunodeficiency. From a large series of ARO patients we selected a Turkish consanguineous family with two siblings affected by ARO and hypogammaglobulinemia with no defects in known osteopetrosis genes. Sequencing of genes involved in the RANKL downstream pathway identified a homozygous mutation in the TNFRSF11A gene in both siblings. Their monocytes failed to differentiate in vitro into osteoclasts upon exposure to M-CSF and RANKL, in keeping with an osteoclast-intrinsic defect. Immunological analysis showed that their hypogammaglobulinemia was associated with impairment in immunoglobulin-secreting B cells. Investigation of other patients revealed a defect in both TNFRSF11A alleles in six additional, unrelated families. Our results indicate that TNFRSF11A mutations can cause a clinical condition in which severe ARO is associated with an immunoglobulin-production defect.

Cohen Syndrome Is Caused by Mutations in a Novel Gene, COH1, Encoding a Transmembrane Protein with a Presumed Role in Vesicle-Mediated Sorting and Intracellular Protein Transport

Cohen syndrome is an uncommon autosomal recessive disorder whose diagnosis is based on the clinical picture of nonprogressive psychomotor retardation and microcephaly, characteristic facial features, retinal dystrophy, and intermittent neutropenia. We have refined the critical region on chromosome 8q22 by haplotype analysis, and we report the characterization of a novel gene, COH1, that is mutated in patients with Cohen syndrome. The longest transcript (14,093 bp) is widely expressed and is transcribed from 62 exons that span a genomic region of approximately 864 kb. COH1 encodes a putative transmembrane protein of 4,022 amino acids, with a complex domain structure. Homology to the Saccharomyces cerevisiae VPS13 protein suggests a role for COH1 in vesicle-mediated sorting and transport of proteins within the cell.