De novo variants predicting haploinsufficiency for DIP2C are associated with expressive speech delay

The disconnected (disco)-interacting protein 2 (DIP2) gene was first identified in D. melanogaster and contains a DNA methyltransferase-associated protein 1 (DMAP1) binding domain, Acyl-CoA synthetase domain and AMP-binding sites. DIP2 regulates axonal bifurcation of the mushroom body neurons in D. melanogaster and is required for axonal regeneration in the neurons of C. elegans. The DIP2 homologues in vertebrates, Disco-interacting protein 2 homolog A (DIP2A), Disco-interacting protein 2 homolog B (DIP2B), and Disco-interacting protein 2 homolog C (DIP2C), are highly conserved and expressed widely in the central nervous system. Although there is evidence that DIP2C plays a role in cognition, reports of pathogenic variants in these genes are rare and their significance is uncertain. We present 23 individuals with heterozygous DIP2C variants, all manifesting developmental delays that primarily affect expressive language and speech articulation. Eight patients had de novo variants predicting loss-of-function in the DIP2C gene, two patients had de novo missense variants, three had paternally inherited loss of function variants and six had maternally inherited loss-of-function variants, while inheritance was unknown for four variants. Four patients had cardiac defects (hypertrophic cardiomyopathy, atrial septal defects, and bicuspid aortic valve). Minor facial anomalies were inconsistent but included a high anterior hairline with a long forehead, broad nasal tip, and ear anomalies. Brainspan analysis showed elevated DIP2C expression in the human neocortex at 10-24 weeks after conception. With the cases presented herein, we provide phenotypic and genotypic data supporting the association between loss-of-function variants in DIP2C with a neurocognitive phenotype.

A Multicenter Analysis of Abnormal Chromosomal Microarray Findings in Congenital Heart Disease

Background Chromosomal microarray analysis (CMA) provides an opportunity to understand genetic causes of congenital heart disease (CHD). The methods for describing cardiac phenotypes in patients with CMA abnormalities have been inconsistent, which may complicate clinical interpretation of abnormal testing results and hinder a more complete understanding of genotype-phenotype relationships. Methods and Results Patients with CHD and abnormal clinical CMA were accrued from 9 pediatric cardiac centers. Highly detailed cardiac phenotypes were systematically classified and analyzed for their association with CMA abnormality. Hierarchical classification of each patient into 1 CHD category facilitated broad analyses. Inclusive classification allowing multiple CHD types per patient provided sensitive descriptions. In 1363 registry patients, 28% had genomic disorders with well-recognized CHD association, 67% had clinically reported copy number variants (CNVs) with rare or no prior CHD association, and 5% had regions of homozygosity without CNV. Hierarchical classification identified expected CHD categories in genomic disorders, as well as uncharacteristic CHDs. Inclusive phenotyping provided sensitive descriptions of patients with multiple CHD types, which occurred commonly. Among CNVs with rare or no prior CHD association, submicroscopic CNVs were enriched for more complex types of CHD compared with large CNVs. The submicroscopic CNVs that contained a curated CHD gene were enriched for left ventricular obstruction or septal defects, whereas CNVs containing a single gene were enriched for conotruncal defects. Neuronal-related pathways were over-represented in single-gene CNVs, including top candidate causative genes NRXN3, ADCY2, and HCN1. Conclusions Intensive cardiac phenotyping in multisite registry data identifies genotype-phenotype associations in CHD patients with abnormal CMA.

Acute myeloid leukemia and dilated cardiomyopathy in a pediatric patient with D-2-hydroxyglutaric aciduria type I

D-2-hydroxyglutaric aciduria (D-2-HGA) is a rare neurometabolic disease with two main subtypes, caused by either inactivating variants in D2HGDH (type I) or germline gain of function variants in IDH2 (type II), that result in accumulation of the same toxic metabolite, D-2-hydroxyglutarate. The main clinical features of both are neurologic, including developmental delay, hypotonia, and seizures. Dilated cardiomyopathy is a unique feature thus far only reported in type II. As somatic variants in IDH2 are frequently identified in several different types of cancer, including acute myeloid leukemia (AML), a link between cancer and this metabolic disease has been proposed; however, there is no reported cancer in patients with either type of D-2-HGA. Murine models have demonstrated how D-2-hydroxyglutarate alters metabolism and epigenetics, a potential mechanism by which this metabolite may cause cancer and cardiomyopathy. Here, we report the first case of both AML and dilated cardiomyopathy in a pediatric patient with D-2-HGA type I, who was treated with an anthracycline-free regimen. This report may expand the clinical spectrum of this rare metabolic disease and provide insight on long-term surveillance and care. However, this case is complicated by the presence of a complex chromosomal rearrangement resulting in a 25.5 Mb duplication of 1q41 and a 2.38 Mb deletion of 2q37.3. Thus, the direct causal relationship between D-2-HGA and leukemogenesis or cardiomyopathy warrants further scrutiny.

Germline variants in tumor suppressor FBXW7 lead to impaired ubiquitination and a neurodevelopmental syndrome

Neurodevelopmental disorders are highly heterogenous conditions resulting from abnormalities of brain architecture and/or function. FBXW7 (F-box and WD-repeat-domain-containing 7), a recognized developmental regulator and tumor suppressor, has been shown to regulate cell-cycle progression and cell growth and survival by targeting substrates including CYCLIN E1/2 and NOTCH for degradation via the ubiquitin proteasome system. We used a genotype-first approach and global data-sharing platforms to identify 35 individuals harboring de novo and inherited FBXW7 germline monoallelic chromosomal deletions and nonsense, frameshift, splice-site, and missense variants associated with a neurodevelopmental syndrome. The FBXW7 neurodevelopmental syndrome is distinguished by global developmental delay, borderline to severe intellectual disability, hypotonia, and gastrointestinal issues. Brain imaging detailed variable underlying structural abnormalities affecting the cerebellum, corpus collosum, and white matter. A crystal-structure model of FBXW7 predicted that missense variants were clustered at the substrate-binding surface of the WD40 domain and that these might reduce FBXW7 substrate binding affinity. Expression of recombinant FBXW7 missense variants in cultured cells demonstrated impaired CYCLIN E1 and CYCLIN E2 turnover. Pan-neuronal knockdown of the Drosophila ortholog, archipelago, impaired learning and neuronal function. Collectively, the data presented herein provide compelling evidence of an F-Box protein-related, phenotypically variable neurodevelopmental disorder associated with monoallelic variants in FBXW7.

Thirty-Year Survival after Cardiac Surgery for Patients with Turner Syndrome

OBJECTIVE

To evaluate long-term survival in patients with Turner syndrome after congenital heart surgery with a focus on left heart obstructive lesions (LHOLs).

STUDY DESIGN

We queried the Pediatric Cardiac Care Consortium, a US-based registry of congenital heart surgery, for patients with Turner syndrome undergoing congenital heart surgery at <21 years of age between 1982 and 2011. Outcomes were obtained from the Pediatric Cardiac Care Consortium and from national death and transplant registries through 2019. Survival of patients with Turner syndrome and nonsyndromic patients with similar LHOL was compared by Kaplan-Meier survival curves and Cox regression adjusted for age, congenital heart disease, and era.

RESULTS

We identified 179 patients with Turner syndrome operated for LHOL: 161 with 2-ventricle lesions (coarctation n = 149, aortic stenosis n = 12) and 18 with hypoplastic left heart (HLH) variants. There were 157 with 2-ventricle LHOL and 6 with HLH survived to discharge. Among survivors to hospital discharge, the 30-year transplant-free survival was 90.4% for Turner syndrome with 2-ventricle lesions and 90.9% for nonsyndromic comparators (adjusted hazard ratio [aHR] 1.15, 95% CI 0.64-2.04). The postdischarge survival for HLH was 33% for Turner syndrome and 51% for nonsyndromic patients, with these numbers being too small for meaningful comparisons. There was a higher risk for cardiovascular disease events in patients with Turner syndrome vs male (aHR 3.72, 95% CI 1.64-8.39) and female comparators (aHR 4.55, 95% CI 1.87-11.06) excluding heart failure deaths.

CONCLUSIONS

The 30-year transplant-free survival is similar for patients with Turner syndrome and nonsyndromic comparators with operated 2-ventricle LHOL without excess congenital heart disease risk. However, patients with Turner Syndrome still face increased cardiovascular disease morbidity, stressing the importance of lifelong comorbidity surveillance in this population.

A Recurrent De Novo Variant in NACC1 Causes a Syndrome Characterized by Infantile Epilepsy, Cataracts, and Profound Developmental Delay

Whole-exome sequencing (WES) has increasingly enabled new pathogenic gene variant identification for undiagnosed neurodevelopmental disorders and provided insights into both gene function and disease biology. Here, we describe seven children with a neurodevelopmental disorder characterized by microcephaly, profound developmental delays and/or intellectual disability, cataracts, severe epilepsy including infantile spasms, irritability, failure to thrive, and stereotypic hand movements. Brain imaging in these individuals reveals delay in myelination and cerebral atrophy. We observe an identical recurrent de novo heterozygous c.892C>T (p.Arg298Trp) variant in the nucleus accumbens associated 1 (NACC1) gene in seven affected individuals. One of the seven individuals is mosaic for this variant. NACC1 encodes a transcriptional repressor implicated in gene expression and has not previously been associated with germline disorders. The probability of finding the same missense NACC1 variant by chance in 7 out of 17,228 individuals who underwent WES for diagnoses of neurodevelopmental phenotypes is extremely small and achieves genome-wide significance (p = 1.25 × 10-14). Selective constraint against missense variants in NACC1 makes this excess of an identical missense variant in all seven individuals more remarkable. Our findings are consistent with a germline recurrent mutational hotspot associated with an allele-specific neurodevelopmental phenotype in NACC1.

Complex Chronic Conditions Among Children Undergoing Cardiac Surgery

Children with complex chronic conditions (CCCs) require a disproportionate amount of inpatient resources and are at increased risk of mortality during hospital admissions. This study examines the impact of non-cardiac, comorbid complex chronic conditions on outcomes in children undergoing congenital heart surgery. All admissions associated with a congenital cardiac surgical procedure in the Kids' Inpatient Database from 1997 to 2012 were examined. Children were classified by the number as well as type (genetic vs. non-genetic) of CCC. Baseline demographics as well as proportion of total inpatient days and total hospitalization charges was assessed. Multivariate regression models examining occurrence of a complication, mortality, prolonged length of stay and high hospitalization charges were constructed. In multivariate models, an increasing number of CCC was associated with increased risk of mortality and complications (mortality: 1 CCC: odds ratio (OR) = 1.17, 95 % CI = 1.03-1.33); ≥2 CCC: OR = 1.54, 95 % CI = 1.26-1.87). Additionally, the presence of a genetic CCC was protective against mortality (OR = 0.71, 95 % CI = 0.56-0.89) while non-genetic CCCs were associated with mortality (OR = 1.62, 95 % CI = 1.41-1.88) and high resource utilization. Over time, the proportion of genetic CCC remained stable while non-genetic CCC increased in prevalence. Complex chronic conditions have a varying association with mortality, morbidity and resource utilization in children undergoing congenital heart surgery. While genetic CCCs were not associated with poor outcomes, non-genetic CCCs were risk factors for morbidity and mortality. These findings suggest that pre-surgical counseling and surgical planning should account for the type of non-cardiac comorbid conditions.

Mutations in HIVEP2 are associated with developmental delay, intellectual disability, and dysmorphic features

Human immunodeficiency virus type I enhancer binding protein 2 (HIVEP2) has been previously associated with intellectual disability and developmental delay in three patients. Here, we describe six patients with developmental delay, intellectual disability, and dysmorphic features with de novo likely gene-damaging variants in HIVEP2 identified by whole-exome sequencing (WES). HIVEP2 encodes a large transcription factor that regulates various neurodevelopmental pathways. Our findings provide further evidence that pathogenic variants in HIVEP2 lead to intellectual disabilities and developmental delay.

Adult surgical experience with Loeys-Dietz syndrome

BACKGROUND

Loeys-Dietz syndrome (LDS) results from mutations in receptors for the cytokine transforming growth factor-β leading to aggressive aortic pathology sometimes accompanied by specific phenotypic features including bifid uvula, hypertelorism, cleft palate, and generalized arterial tortuosity. We reviewed our adult surgical experience with LDS in order to validate current recommendations regarding management of this newly described disease.

METHODS

All adult (≥ 18 years old) patients with LDS undergoing surgical treatment at a single referral institution from September 1999 to May 2013 were retrospectively reviewed.

RESULTS

Eleven adult LDS patients were identified by clinical criteria and genotyping. Seven (64%) experienced acute type A dissection at some point in their lives. All eventually required aortic root replacement, and 73% required multiple vascular surgical interventions. Over a mean follow-up of 65 ± 49 months, 2.8 cardiovascular procedures per patient were performed. In patients with type A dissection, a mean of 3.4 operations were performed versus 1.8 operations for patients without dissection. Total aortic replacement was required in 5 patients (45%) and 2 (18%) required neurosurgical intervention for cerebrovascular pathology. There was 1 late death from infectious complications, and no deaths from vascular catastrophe.

CONCLUSIONS

These results confirm the aggressive nature of LDS aortic pathology. However, the improved survival compared with earlier LDS reports suggest that aggressive treatment strategies may alter outcomes and improve the natural history of this syndrome.

Atenolol versus losartan in children and young adults with Marfan's syndrome

BACKGROUND

Aortic-root dissection is the leading cause of death in Marfan's syndrome. Studies suggest that with regard to slowing aortic-root enlargement, losartan may be more effective than beta-blockers, the current standard therapy in most centers.

METHODS

We conducted a randomized trial comparing losartan with atenolol in children and young adults with Marfan's syndrome. The primary outcome was the rate of aortic-root enlargement, expressed as the change in the maximum aortic-root-diameter z score indexed to body-surface area (hereafter, aortic-root z score) over a 3-year period. Secondary outcomes included the rate of change in the absolute diameter of the aortic root; the rate of change in aortic regurgitation; the time to aortic dissection, aortic-root surgery, or death; somatic growth; and the incidence of adverse events.

RESULTS

From January 2007 through February 2011, a total of 21 clinical centers enrolled 608 participants, 6 months to 25 years of age (mean [±SD] age, 11.5±6.5 years in the atenolol group and 11.0±6.2 years in the losartan group), who had an aortic-root z score greater than 3.0. The baseline-adjusted rate of change in the mean (±SE) aortic-root z score did not differ significantly between the atenolol group and the losartan group (-0.139±0.013 and -0.107±0.013 standard-deviation units per year, respectively; P=0.08). Both slopes were significantly less than zero, indicating a decrease in the aortic-root diameter relative to body-surface area with either treatment. The 3-year rates of aortic-root surgery, aortic dissection, death, and a composite of these events did not differ significantly between the two treatment groups.

CONCLUSIONS

Among children and young adults with Marfan's syndrome who were randomly assigned to losartan or atenolol, we found no significant difference in the rate of aortic-root dilatation between the two treatment groups over a 3-year period. (Funded by the National Heart, Lung, and Blood Institute and others; ClinicalTrials.gov number, NCT00429364.).

Characteristics of children and young adults with Marfan syndrome and aortic root dilation in a randomized trial comparing atenolol and losartan therapy

BACKGROUND

The Pediatric Heart Network designed a clinical trial to compare aortic root growth and other short-term cardiovascular outcomes in children and young adults with Marfan syndrome randomized to receive atenolol or losartan. We report here the characteristics of the screened population and enrolled subjects.

METHODS AND RESULTS

Between 2007 and 2011, 21 clinical sites randomized 608 subjects, aged 6 months to 25 years who met the original Ghent criteria and had a body surface area-adjusted aortic root diameter z-score >3.0. The mean age at study entry was 11.2 years, 60% were male, and 25% were older teenagers and young adults. The median aortic root diameter z-score was 4.0. Aortic root diameter z-score did not vary with age. Mitral valve prolapse and mitral regurgitation were more common in females. Among those with a positive family history, 56% had a family member with aortic surgery, and 32% had a family member with a history of aortic dissection.

CONCLUSIONS

Baseline demographic, clinical, and anthropometric characteristics of the randomized cohort are representative of patients in this population with moderate to severe aortic root dilation. The high percentage of young subjects with relatives who have had aortic dissection or surgery illustrates the need for more definitive therapy; we expect that the results of the study and the wealth of systematic data collected will make an important contribution to the management of individuals with Marfan syndrome.

Two-stage total aortic replacement for Loeys-Dietz syndrome

Loeys-Dietz syndrome (LDS) is a recently described connective tissue disorder characterized by generalized arterial tortuosity and aggressive aortopathy that untreated leads to early death even at aortic dimensions as small as 4 cm. We report the case of a young man with LDS successfully treated for aortic root, arch, and thoracoabdominal pathology.

Two-Stage Total Aortic Replacement for Loeys-Dietz Syndrome

Abstract Loeys-Dietz syndrome (LDS) is a recently described connective tissue disorder characterized by generalized arterial tortuosity and aggressive aortopathy that untreated leads to early death even at aortic dimensions as small as 4 cm. We report the case of a young man with LDS successfully treated for aortic root, arch, and thoracoabdominal pathology.(J Card Surg ****;**:**-**).

Hemolytic anemia secondary to modified blalock-taussig shunt

The Norwood procedure with a modified Blalock-Taussig shunt (MBTS) is the first of the three-stage surgical palliation for infants with hypoplastic left heart syndrome. We report a patient with schistocytic hemolytic anemia that developed following a right MBTS with a Gore-Tex graft. Hemolysis associated with a MBTS has not been previously reported in the literature. Multiple packed red blood cell transfusions were required due to desaturation and hypoxemia. Hemi-Fontan procedure was performed early for chronic anemia. Hemolysis resolved post operatively even though the patient subsequently required a Gore-Tex central shunt for persistent cyanosis.

Ventricular arrhythmia in the X-linked cardiomyopathy Barth syndrome

Barth syndrome is an X-linked disorder characterized by dilated cardiomyopathy, cyclic neutropenia, skeletal myopathy, abnormal mitochondria, and growth deficiency. The primary defect is a mutation in the TAZ gene on the X chromosome at Xq28, resulting in abnormal phospholipid biosynthesis and cardiolipin deficiency. To date, there has been no systematic evaluation of the cardiac phenotype. We report five cases of cardiac arrest and/or placement of an internal cardiac defibrillator with documented ventricular arrhythmia. We suggest that ventricular arrhythmia is part of the primary phenotype of the disorder and that patients should be screened accordingly.

Tibial aplasia, lower extremity mirror image polydactyly, brachyphalangy, craniofacial dysmorphism and genital hypoplasia: further delineation and mutational analysis

Congenital anomalies involving tibial aplasia are rare. Recently, four children with an unusual combination of limb anomalies, facial dysmorphism and genital hypoplasia have been reported. All affected children reported were male. One case noted father to son transmission, implying autosomal dominant inheritance. We report the first female patient with this syndrome. The patient had tibial aplasia, mirror image preaxial polydactyly involving her feet, brachyphalangy, genital hypoplasia as well as facial dysmorphism including telecanthus, blepharophimosis, a flat nasal bridge with a small nose and a small mouth. Consistent with reports in males of a micropenis and hypoplastic scrotum, our patient had absent labia minora and a very small clitoris. Her father had very minor anomalies suggestive of somatic mosaicism or marked variability. Mouse models affecting limb development are powerful tools in the study of human syndromes. The clinical phenotype of patients with this syndrome is reminiscent of some luxoid mouse mutants suggesting Alx4 and related members of the paired homeodomain class as candidate genes. ALX4 haploinsufficiency in humans causes parietal foramina, which one patient with this syndrome was reported to have. Sequencing of coding exons of ALX4 and its related homologue, ALX3, in the proband failed to reveal coding sequence alterations. Our father/daughter pair is the second family reported, supporting a dominant mode of inheritance. Moreover, the very mild phenotype in the father suggests the need for very careful attention to parental examination in such cases.

Myocardial immediate early gene activation after cardiopulmonary bypass with cardiac ischemia-reperfusion

BACKGROUND

The inflammatory process after cardiopulmonary bypass is accompanied by alterations in gene expression for various inflammatory mediators.

METHODS

To analyze differential gene expression after myocardial ischemia-reperfusion, subtraction hybridization was used to discover induction of TIS7/PC4, an immediate early gene heretofore not observed in the heart. This prompted characterization of the related immediate early genes c-fos and c-jun, by Northern analysis and in situ hybridization in human and lamb myocardium subjected to cardiopulmonary bypass with myocardial ischemia. For comparison, we analyzed expression of inducible nitric oxide synthase (iNOS), which requires cytokine-activation, resulting in a "delayed" response.

RESULTS

In ischemic-reperfused myocardium at endcardiopulmonary bypass, c-fos, c-jun, and TIS7/PC4 were induced, whereas iNOS transcripts were undetectable. Expression patterns of c-fos and c-jun by in situ hybridization were markedly different; myocardial c-fos expression was diffuse and homogeneous, whereas c-jun expression was patchy with areas of intense focal localization.

CONCLUSIONS

Cardiopulmonary bypass with myocardial ischemia rapidly induces the immediate early genes TIS7/PC4 (discovered by subtraction hybridization), and c-fos and c-jun (precursors to the transcriptional regulator AP-1). Immediate early genes presumably contribute to activation of inflammatory mediators after cardiopulmonary bypass and differences in their tissue expression patterns, as observed for c-fos and c-jun, presumably modulate their effect upon downstream gene activation.

Complex modular cis-acting elements regulate expression of the cardiac specifying homeobox gene Csx/Nkx2.5

The murine homeobox gene Csx/Nkx2.5 is an evolutionarily highly conserved gene related to the Drosophila tinman gene, which specifies cardiac and visceral mesoderm. Since Csx/Nkx2.5 plays an essential role in heart development, studying its regulation is essential for the better understanding of molecular mechanisms of cardiogenesis and the pathogenesis of congenital heart disease in humans. In this study, we characterized the murine Csx/Nkx2.5 gene and identified two novel untranslated exons, 1a, and 1b, resulting in three different Csx/Nkx2.5 transcripts. To examine the tissue-specific transcriptional regulation in vivo, we analyzed a total of 23 kb of Csx/Nkx2.5 upstream and downstream sequences by generating transgenic embryos carrying lacZ reporter constructs containing various lengths of flanking sequence. With 14 kb of 5′ flanking sequence, lacZ expression was observed in the cardiac crescent at E7.5, and in the outflow tract, the interatrial groove, the atrioventricular canal and right and left ventricles, as well as in pharyngeal floor, thyroid primordia, and stomach at E10.5. In adult animals, lacZ expression of the transgene was limited to the atrioventricular junction and the subendocardium of the ventricular septum. Reducing the size of flanking sequence to 3.3 kb of intron 2 restricted lacZ expression to the outflow tract and the basal part of the right ventricle in E10.5 embryos. In contrast, the addition of 6 kb of 3′ flanking sequence caused strong expression of the reporter gene in the entire right ventricle. Interestingly, Csx/Nkx2. 5 seems to be negatively regulated by its own gene product, because when lacZ was “knocked-in” to replace the entire coding exons, lacZ expression was much higher in the heart of homozygous embryos than that in the heterozygote. These results indicate that the transcriptional regulatory elements of Csx/Nkx 2.5 seems unexpectedly highly modular, and is temporally regulated in a dynamic manner by different enhancer regions. Since Csx/Nkx2.5-like genes are expressed in all species having a heart, their complex modular organization with multiple enhancers probably reflects progressive addition of regulatory elements during the evolution from a simple heart tube to a complex four-chambered organ.

Molecular cloning, chromosomal mapping, and characterization of the human cardiac-specific homeobox gene hCsx

BACKGROUND

Csx/Nkx2.5, a murine nonclustered homeobox gene expressed primarily in the heart, has significant sequence similarity to the Drosophila tinman gene. Tinman is essential for heart and gut formation in Drosophila. Targeted mutation in the mouse gene, Csx/Nkx2.5, arrests cardiac development during early embryonic stages, suggesting an evolutionary conservation in cardiogenesis.

MATERIALS AND METHODS

We have isolated and characterized a human homolog, hCsx, from an adult cardiac cDNA library. Northern blotting and ribonuclease protection was used to define the pattern of expression during normal development and in disease states. Chromosomal localization of the gene was determined by somatic cell hybrid analysis and fluorescent in situ hybridization.

RESULTS

The predicted amino acid sequence of hCsx has 87% overall homology to the murine gene with 100% identity in the homeodomain. The homeodomain sequence of hCsx is 95% identical to its Xenopus homolog, and 65% to tinman. hCsx mRNA was detected exclusively in the heart. hCsx transcript was detected at 12 weeks in human embryonic heart, the earliest time point examined, and was up-regulated 5-fold between 12 and 19 weeks. There was no significant alteration of hCsx message level in the myocardium of 14 patients with end stage heart failure compared to a normal control. The human gene mapped to the distal portion of chromosome 5, the 5q34-q35 region. This defines a new synteny region between human chromosome 5q and the t-locus of mouse chromosome 17, where the mouse Csx gene is located.

CONCLUSIONS

hCsx, the human homolog of Drosophila tinman, is expressed in heart in a tissue restricted manner. Distal 5q trisomies produce several phenotypic abnormalities, including a high incidence of congenital heart disease. Isolation of the hCsx gene will allow further studies of mutations in this gene and their potential associations with some forms of congenital heart disease in humans.