Genetic variation in brain-derived neurotrophic factor and human fear conditioning.

Brain-derived neurotrophic factor (BDNF) has been implicated in hippocampal-dependent learning processes, and carriers of the Met allele of the Val66Met BDNF genotype are characterized by reduced hippocampal structure and function. Recent nonhuman animal work suggests that BDNF is also crucial for amygdala-dependent associative learning. The present study sought to examine fear conditioning as a function of the BDNF polymorphism. Fifty-seven participants were genotyped for the BDNF polymorphism and took part in a differential-conditioning paradigm. Participants were shocked following a particular conditioned stimulus (CS+) and were also presented with stimuli that ranged in perceptual similarity to the CS+ (20, 40 or 60% smaller or larger than the CS+). The eye blink component of the startle response was measured to quantify fear conditioning; post-task shock likelihood ratings for each stimulus were also obtained. All participants reported that shock likelihood varied with perceptual similarity to the CS+ and showed potentiated startle in response to CS +/- 20% stimuli. However, only the Val/Val group had potentiated startle responses to the CS+. Met allele carrying individuals were characterized by deficient fear conditioning--evidenced by an attenuated startle response to CS+ stimuli. Variation in the BDNF genotype appears related to abnormal fear conditioning, consistent with nonhuman animal work on the importance of BDNF in amygdala-dependent associative learning. The relation between genetic variation in BDNF and amygdala-dependent associative learning deficits is discussed in terms of potential mechanisms of risk for psychopathology.

Toriello-Carey syndrome in a patient with a de novo balanced translocation [46,XY,t(2;14)(q33;q22)] interrupting SATB2.

Toriello-Carey syndrome (TCS; OMIM 217980) is a multiple congenital anomaly syndrome characterized by the common manifestations of corpus callosum agenesis, cardiac defects, cleft palate/Robin sequence, hypotonia, mental retardation, postnatal growth retardation and distinctive facial dysmorphology (including micrognathia, telecanthus, small nose and full cheeks). Both autosomal recessive and X-linked inheritance have been proposed, but chromosomal abnormalities involving disparate loci have also been detected in a small number of cases. We report a patient with classical features of TCS and an apparently balanced de novo translocation between chromosomes 2 and 14 [46,XY,t(2;14)(q33;q22)]. Molecular characterization revealed direct interruption of the special AT-rich sequence-binding protein-2 (SATB2) gene at the 2q33.1 translocation breakpoint, while the 14q22.3 breakpoint was not intragenic. SATB2 mutation or deletion has been associated with both isolated and syndromic facial clefting; however, an association with TCS has not been reported. SATB2 functions broadly as a transcription regulator, and its expression patterns suggest an important role in craniofacial and central nervous system development, making it a plausible candidate gene for TCS.

Disruption of contactin 4 in three subjects with autism spectrum disorder.

BACKGROUND: Autism spectrum disorder (ASD) is a developmental disorder of the central nervous system of largely unknown aetiology. The prevalence of the syndrome underscores the need for biological markers and a clearer understanding of pathogenesis. For these reasons, a genetic study of idiopathic ASD was undertaken. METHODS AND RESULTS: Array based comparative genomic hybridisation identified a paternally inherited chromosome 3 copy number variation (CNV) in three SUBJECTS: a deletion in two siblings and a duplication in a third, unrelated individual. These variations were fluorescence in situ hybridisation (FISH) validated and the end points further delineated using a custom fine tiling oligonucleotide array. Polymerase chain reaction (PCR) products unique to the rearrangements were amplified and sequence analysis revealed the variations to have resulted from Alu Y mediated unequal recombinations interrupting contactin 4 (CNTN4). CONCLUSION: CNTN4 plays an essential role in the formation, maintenance, and plasticity of neuronal networks. Disruption of this gene is known to cause developmental delay and mental retardation. This report suggests that mutations affecting CNTN4 function may be relevant to ASD pathogenesis.

An improved method for generating BAC DNA suitable for FISH.

Fluorescence in situ hybridization (FISH) is commonly used to identify chromosomal aberrations such as translocations, deletions, duplications, gene fusions, and aneuploidies. It relies on the hybridization of fluorescently labeled DNA probes onto denatured metaphase chromosomes or interphase nuclei. These probes are often generated from DNA sequences cloned within bacterial artificial chromosomes (BACs). Growing these BACs in adequate amounts for FISH can be demanding. We describe FISH performed with bacteriophage Phi29 DNA polymerase amplified BAC DNA. Generating this material required significantly smaller cultures and less time than standard methods. The FISH results obtained were comparable with those obtained from standard BAC DNA. We believe this method of BAC DNA generation is useful for the entire FISH community as it improves considerably on prior methods.

17p11.2p12 triplication and del(17)q11.2q12 in a severely affected child with dup(17)p11.2p12 syndrome.

Multiple congenital anomalies/mental retardation syndromes due to genomic rearrangements involving chromosome 17p11.2 include deletion resulting in Smith-Magenis syndrome and a reciprocal duplication of the same region resulting in the 17p11.2 duplication syndrome. We present the clinical and molecular analysis of an 8-year-old male with a dup(17p11.2p12) who was evaluated for unusual severity of the phenotype. Fluorescent in situ hybridization (FISH) analysis not only confirmed the 17p duplication but also identified an approximately 25% mosaicism for tetrasomy 17p11.2p12. Whole-genome array comparative genomic hybridization (aCGH) was performed to identify other genomic rearrangements possibly contributing to the severe phenotype and the unusual features in the patient. The 17p duplication was determined by FISH and aCGH to encompass approximately 7.5 Mb, from COX10 to KCNJ12. An approximately 830 Kb deletion of 17q11.2q12, including exon 1 of an amiloride-sensitive cation channel neuronal gene, ACCN1, was also identified by aCGH; breakpoints of the deletion were confirmed by FISH. Sequencing the non-deleted allele of ACCN1 did not show any mutations. Western analysis of human tissue-specific proteins revealed that ACCN1 is expressed not only in the brain as previously reported but also in all tissues examined, including heart, liver, kidneys, and spleen. The large-sized 17p11.2p12 duplication, partial triplication of the same region, and the 17q11.2q12 deletion create a complex chromosome 17 rearrangement that has not been previously identified. This is the first case of triplication reported for this chromosome. Our study emphasizes the utility of whole-genome analysis for known cases with deletion/duplication syndromes with unusual or severe phenotypes.

Autism and environmental genomics.

Autism spectrum disorders (ASD) are defined by behavior and diagnosed by clinical history and observation but have no biomarkers and are presumably, etiologically and biologically heterogeneous. Given brain abnormalities and high monozygotic concordance, ASDs have been framed as neurobiologically based and highly genetic, which has shaped the research agenda and in particular criteria for choosing candidate ASD genes. Genetic studies to date have not uncovered genes of strong effect, but a move toward "genetic complexity" at the neurobiological level may not suffice, as evidence of systemic abnormalities (e.g. gastrointestinal and immune), increasing rates and less than 100% monozygotic concordance support a more inclusive reframing of autism as a multisystem disorder with genetic influence and environmental contributors. We review this evidence and also use a bioinformatic approach to explore the possibility that "environmentally responsive genes" not specifically associated with the nervous system, but potentially associated with systemic changes in autism, have not hitherto received sufficient attention in autism genetics investigations. We overlapped genes from NIEHS Environmental Genome Project, the Comparative Toxicogenomics Database, and the SeattleSNPs database of genes relevant to the human immune and inflammatory response with linkage regions identified in published autism genome scans. We identified 135 genes in overlap regions, of which 56 had never previously been studied in relation to autism and 47 had functional SNPs (in coding regions). Both our review and the bioinformatics exercise support the expansion of criteria for evaluating the relevance of genes to autism risk to include genes related to systemic impact and environmental responsiveness. This review also suggests the utility of environmental genomic resources in highlighting the potential relevance of particular genes within linkage regions. Environmental responsiveness and systems impacts consistent with system-wide findings in autism are thus supported as important considerations in identifying the numerous and complex modes of gene-environment interaction in autism.

X-linked sideroblastic anaemia with ataxia: another mitochondrial disease?

OBJECTIVES: The syndrome of X-linked sideroblastic anaemia with ataxia is rare, described only twice in the literature. The aim was to obtain clinical neurological and haematological data about this rare syndrome throughout adult life. METHODS: A family is described with two affected brothers and two affected maternal uncles. The family was evaluated clinically. Haematological investigations included full blood count, blood film, iron studies, free erythrocyte protoporphyrin (FEP) concentrations and a bone marrow examination where possible. RESULTS: Core neurological features included motor delay, ataxia evident from early childhood, and dysarthria. Neurological features were non-progressive until the fifth decade when slow progression became evident. Some family members showed mild spasticity. Patients usually have a mild asymptomatic anaemia or a borderline decreased mean corpuscular volume. Blood film examination showed Pappenheimer bodies. Bone marrow examination showed ring sideroblasts, indicating raised erythrocyte iron. Free erythrocyte protoporphyrin (FEP) concentrations were raised. CONCLUSIONS: Haematological features are subtle and can be easily overlooked, and individual patients may not display all the abnormal features. X-linked ataxias are rare and incorrect genetic advice may be given if the diagnostic haematological features of X-linked sideroblastic anaemia are overlooked. Males with early onset ataxia should have a haematological evaluation including a blood film, with a bone marrow examination if abnormal blood count indices and measurement of FEP concentrations raise suspicion. The condition has parallels with Pearson's syndrome and Friedreich's ataxia. All three conditions are associated with mitochondrial iron handling defects and ataxia. The human ATP binding cassette gene (hABC7) is a candidate gene and requires further investigation.

Locus heterogeneity in autosomal dominant congenital external ophthalmoplegia (CFEOM).

Congenital external ophthalmoplegia (CFEOM) is an uncommon autosomal dominant condition that has previously been mapped to the pericentromeric region of chromosome 12 in seven families with no evidence of locus heterogeneity. We report three families with typical CFEOM. One family does not map to this region of chromosome 12 or to other chromosomal locations implicated in disorders of lid or ocular movement. Recombinants in two CFEOM families potentially help to reduce the size of the candidate region on chromosome 12.

Phenotypic heterogeneity may occur in congenital fibrosis of the extraocular muscles.

BACKGROUND/AIMS: Congenital fibrosis of the extraocular muscles (CFEOM) is an autosomal dominant, non-progressive disorder characterised by congenital ptosis and external ophthalmoplegia. CFEOM has previously been divided into several clinical entities; general fibrosis syndrome, strabismus fixus, vertical retraction syndrome, and congenital fibrosis of the inferior rectus. The purpose of this study was to identify families with CFEOM in this geographical region in order to perform a study of the clinical presentation of this disorder and to estimate its minimum prevalence in the population. METHODS: Four families were identified with CFEOM in the Wessex region from whom a full history with a pedigree was obtained. All individuals underwent ophthalmological examination. RESULTS/CONCLUSION: This study shows that several of the CFEOM entities can be present within one family suggesting that these are variants of the same condition. It is suggested that subclassification is, therefore, not appropriate. The minimum prevalence of this disorder was found to be 1/230,000.

Molecular confirmation of germ line mosaicism for a submicroscopic deletion of chromosome 22q11.

Submicroscopic deletions of chromosome 22q11 have been reported in a multiple anomaly syndrome variously labelled as velocardiofacial syndrome, conotruncal anomaly face syndrome, and Di George syndrome. Most 22q11 microdeletions occur sporadically, although in some cases the deletion may be transmitted. We describe two affected sibs with confirmed 22q11 deletions from unaffected parents who are not deleted. Haplotype analysis demonstrates that the deletion in the affected sibs has occurred on the same maternal chromosome 22. Furthermore, an unaffected sib was found to have inherited the same maternal haplotype at 22q11 in an undeleted form. This is the first molecular demonstration of germ line mosaicism for a microdeletion at chromosome 22q11 and highlights the need for caution in estimation of recurrence risks, even when constitutional deletions have been excluded on parental analysis.

Spectrum of clinical features associated with interstitial chromosome 22q11 deletions: a European collaborative study.

We present clinical data on 558 patients with deletions within the DiGeorge syndrome critical region of chromosome 22q11. Twenty-eight percent of the cases where parents had been tested had inherited deletions, with a marked excess of maternally inherited deletions (maternal 61, paternal 18). Eight percent of the patients had died, over half of these within a month of birth and the majority within 6 months. All but one of the deaths were the result of congenital heart disease. Clinically significant immunological problems were very uncommon. Nine percent of patients had cleft palate and 32% had velopharyngeal insufficiency, 60% of patients were hypocalcaemic, 75% of patients had cardiac problems, and 36% of patients who had abdominal ultrasound had a renal abnormality. Sixty-two percent of surviving patients were developmentally normal or had only mild learning problems. The majority of patients were constitutionally small, with 36% of patients below the 3rd centile for either height or weight parameters.

Extending the overlap of three congenital overgrowth syndromes.

We present the case of a male infant, born prematurely (at 33 weeks gestation) with macrosomia, disproportionate macrocephaly, facial dysmorphism, short penis and a small umbilical defect. He had a large ASD and was ventilated from birth for respiratory distress syndrome. He died at 12 hours of age despite neonatal ITU care. Post-mortem examination showed highly lobulated kidneys with nodules of blastema and foci of hamartomatous change in the medulla. Prominence of pancreatic islet cells and expansion of hepatic portal tracts were also noted. His mother has minor cervical spine abnormalities. We discuss the differential diagnosis and the difficulty in confidently assigning a diagnosis to this patient, as considerable overlap is becoming evident between Simpson-Golabi-Behmel syndrome and Perlman syndrome.

Linkage analysis in 16 families with incontinentia pigmenti.

A locus for the X-linked dominant genodermatosis incontinentia pigmenti (IP) has been linked to markers in Xq28. Here we report high lod scores for markers spanning the interval DXS52-DXYS154 using 16 families, providing further evidence for a single major X-linked IP locus.

RDCI, the vasoactive intestinal peptide receptor: a candidate gene for the features of Albright hereditary osteodystrophy associated with deletion of 2q37.

Albright hereditary osteodystrophy (AHO) is an autosomal dominant disorder characterised by the presence of brachymetaphalangism, short stature, obesity, and mental retardation. Variable biochemical changes many represent either pseudohypoparathyroidism (PHP) owing to resistance to parathormone (PTH) or pseudopseudohypoparathyroidism (PPHP) with no hormone resistance. In most cases of AHO, reduced levels of Gs alpha have been found and a number of deactivating mutations in the gene for Gs alpha located on chromosome 20q13 have been described. Recently a number of people with an AHO-like phenotype have been reported in whom a deletion of chromosomal region 2q37 has been found in the absence of biochemical abnormalities or a reduction in Gs alpha activity. We present a further female patient with a cytogenetically visible deletion of 2q37, an AHO-like phenotype, and unusual biochemistry suggesting moderate PTH resistance. The vasoactive intestinal peptide receptor (RDCI) has recently been mapped to 2q37 and we propose that this is a candidate gene, hemizygosity of which affects signal transduction and leads to the AHO-like phenotype found in patients with 2q37 deletions.

Localization of human liver 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB1) within a YAC contig in Xp11.21.

6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2) catalyzes the synthesis and degradation of fructose-2,6-bisphosphate, a potent regulator of glycolysis. Previous studies assigned the gene for human liver PFK-2/FBPase-2 (HGMW-approved symbol PFKFB1) to the X chromosome; however, precise localization remained ambiguous, with the gene variously placed between Xcen-q13, Xq27-q28, and Xp11.22-p11.21. We have localized the gene within a YAC contig clustered around ALAS2 (human erythroid delta-aminolevulinate synthase) in Xp11.21 and have identified eight YACs positive for the gene. Four of these overlapping YACs were mapped using rare-cutter restriction enzymes to provide in-depth characterization of an 820-kb region encompassing the PFK-2/ FBPase-2 and ALAS2 genes. PFK-2/FBPase-2 was found to lie close (within approx. 250 kb) and telomeric to ALAS2. Three putative CpG islands were also detected in the region.

Importance of microdeletions of chromosomal region 22q11 as a cause of selected malformations of the ventricular outflow tracts and aortic arch: a three-year prospective study.

OBJECTIVES: To assess the incidence of microdeletions of chromosomal region 22q11 in a population of infants coming to a regional pediatric cardiac center with selected abnormalities of the ventricular outflow tracts and aortic arch and, further, to provide phenotypic/genetic correlations to determine whether patients with 22q11 deletions can be clinically recognized in infancy. BACKGROUND: DiGeorge syndrome and velocardiofacial syndrome are frequently associated with malformations of the ventricular outflow tracts and aortic arch. Both are usually caused by microdeletions of chromosomal region 22q11. The overall importance of such deletions as a cause of these cardiac malformations remains to be established. STUDY DESIGN: All infants with the candidate cardiac phenotypes during a 34-month period were studied. Dysmorphic features, type of cardiac defect, serum calcium concentration, and thymic status were recorded. Cytogenetic studies, including high-resolution karyotyping and fluorescence in situ hybridization using cosmids (cEO or cH748) from the DiGeorge critical region, were performed after clinical assessment. RESULTS: Fifty infants (including 36 with tetralogy of Fallot with or without pulmonary atresia) were seen during the study period. Twenty-six infants (52%) were dysmorphic, including 19 who were considered to have a phenotypic appearance consistent with 22q11 deletion. Genetic analysis confirmed hemizygosity for 22q11 in 8 of these 19 cases. Results of fluorescence in situ hybridization studies were normal in 22 infants without dysmorphic features and in 5 infants with dysmorphic features not suggestive of a 22q11 deletion. CONCLUSIONS: Microdeletions of chromosomal region 22q11 are an important cause of selected malformations of the ventricular outflow tracts and aortic arch and account for about 15% to 20% of cases. These deletions may be clinically recognized in early infancy and can be rapidly confirmed by fluorescence in situ hybridization.