Genetics of Congenital Heart Disease 张咸宁 Tel ： ; Office: A705, Research Building 2013/03

Required Reading Thompson &Thompson Genetics in Medicine, 7 th Ed （双语版， 2009 ） ● Pages 、 、 356

Learning Objectives To recognize familial patterns of CHD To understand developmental mechanisms of CHD To see CHDs as examples of the larger group of common disorders with common complex inheritance involving –Single genes –Multiple genes –Environmental influences

Overview Introduction to Congenital Heart Disease (CHD) Developmental Mechanisms –Flow Lesions –Problems in Cell Migration –Problems in Cell Death –Abnormalities in Extracellular Matrix –Abnormalities in Targeted Growth Summary

Introduction to CHD Relatively common birth defect –Liveborn infants 4-8/1 000 –Stillborns 10× higher or 8% –Miscarriages 15% in abortuses <24 weeks gestation

Introduction to CHD Variety of causes –Single gene –Chromosomal –Teratogen exposures Maternal rubella infection Gestational diabetes mellitus

Maternal Infections –Rubella: 35% affected Maternal Diseases –Diabetes Mellitus: 3-5% –Maternal PKU: 10% Teratogenic Substances –Alcohol: 25-35% –Dilantin （苯妥英） : 2-3% Environmental Component

Gross Chromosomal Defects –5-8% of Defects –Examples Trisomy 21: 35-50% Trisomy 18: 99% Turner syndrome: 20% Single-Gene Defects –3% of Defects Genetic Component

Familial Patterns of Recurrence CHD recurrence in a family –Affected individuals may not have identical anatomical heart abnormality –Will have lesions representing similarity in the developmental mechanism Should look for abnormalities outside of the cardiovascular system –May indicate a syndromic association with CHD

Developmental Mechanisms Flow Lesions Problems in Cell Migration Problems in Cell Death Abnormalities in Extracellular Matrix Abnormalities in Targeted Growth

Is Isolated CHD a Multifactorial Trait? Table 8-12: Population Incidence and Recurrence Risks for Various Flow Lesions VSD = Ventricular Septal Defect PDA = Patent Ductus Arteriosus ASD = Atrial Septal Defect AS = Aortic Stenosis DefectPop Incid (%) Freq in Sibs (%) λ sib VSD PDA ASD AS

Is Isolated CHD a Multifactorial Trait? For these flow lesions –Sib relative risk ratio (λ sib ) Support familial aggregation –Where genetic mutation not known Use empiric risk factors to counsel first degree relatives Rapid decrease in risk for second and third degree relatives to not much higher than population risks For families with CHD other than flow lesions –Reassure that recurrence risk is no greater than population risk Prenatal ultrasound can be used as part of counseling and often reassurance before birth

Flow Lesions Large category of CHDs –Approximately 50% of all CHDs Up to 25% of flow lesion CHDs, particularly tetralogy of Fallot, have del22q11.2 –DiGeorge syndrome –Velocardiofacial syndrome –Conotruncal anomaly face syndrome

del22q11.2 Syndromes Autosomal dominant Variable expressivity Deletion of approximately 3 Mb –Caused by homologous recombination of low copy repeat sequences One of the most common cytogenetic deletions with a significant phenotype –1 per – live births

22q11.2 Rearrangements Fig 6-9

del22q11.2 Syndromes Phenotypes may include –CHD –Craniofacial abnormalities –Mental retardation/developmental delay –Reduced circulating lymphocytes –Hypocalcemia –Schizophrenia

del22q11.2 and CHD Responsible for between 5% and 12.5% of CHDs Particularly common in certain CHDs – >40% of patients with tetralogy of Fallot (TOF) and pulmonary atresia (PA) – >60% of patients with TOF and absent pulmonary valve

DGS TDR (Typically Deleted Region) 3 Mb deletion –Loss of approximately 30 genes Smaller 1.5 Mb deletion –Seen in approximately 10% of patients TBX1 maps in DGS TDR –Encodes transcription factor involved in pharyngeal arch development –Haploinsufficiency implicated in DGS –Mutated in patients with similar phenotype who do not have del22q11.2

Apoptosis and CHD TBX1 may be involved in apoptosis, a mechanism known to be involved in normal cardiac and lymphocyte development –Foxp1 in mice Required for remodeling of endocardial cushions (portions of ventricular septum and cardiac outflow tract) To position aortic and pulmonary vessels normally by eliminating certain cells to shift the cushions’ positions –Apoptosis occurs during immune system development To eliminate lymphocytic lineages that react to self Required for protection against autoimmune disease

Apoptosis and CHD If TBX1 causes the conotruncal defects (e.g. TOF) associated with del22q11.2, and if the mechanism is apoptosis, then what does that do to our “developmental mechanisms” outlined at the beginning –del22q11.2 causes the largest proportion of flow lesions, but may be a problem in cell death

4-m.o. Female Infant –CHF from a Large VSD –Dysmorphic Appearance –Family History: Sib and Half-Sib with CHD –Mother with Multiple Psychiatric Admissions Case #1 Truncus Arteriosus TOFVSD

DiGeorge (not DiGeorge’s) Syndrome Features Include: –Cardiac: Conotruncal Defects –Immunologic: Thymic Aplasia or Hypoplasia –Hypocalcemia: Parathyroid Absence or Hypoplasia –Dysmorphism: Hypertelorism, Short Philtrum, Cupid’s Bow Mouth, Ear Anomalies DiGeorge Syndrome

Features Include: –Cardiac: VSD, Tetralogy of Fallot, Rt. Aortic Arch –Cleft Palate: Overt or Submucosal –Development Delay: Mild-to-Moderate, esp. Speech –Dysmorphisms: Prominent Nose, Abnormal Ears, Abundant Hair, Tapered Fingers VeloCardioFacial (VCF) Syndrome

VCF/DG SYNDROMES Clinical Overlap Cleft Palate Dev. Delay DGS Cleft Palate Dev. Delay VCF Facies CHD Dev. Delay VCF Facies

Problems in Cell Migration: Patent Ductus Arteriosus (PDA) 1 in Fullterm Infants 10% of CHD 2:1 Female to Male Ratio Multifactorial Etiology: Genes and Environment

Familial PDA 2-y.o. Palestinian Boy –Patent Ductus Arteriosus –Positive Family History PDA

Neural Crest Cell Migration and Cardiac Development

Cardiac Genetics Population Perspective Developing Innovative Therapies –Postnatal Interventions Marfan Syndrome: Anti-TGF  –Prenatal Interventions Folate Improving Clinical Trials Research –Cardiology Emulating Heme/Onc –Primary Endpoints - Function, Not Survival –Better Statistical Power

First, exome-centered and whole-genome next-generation sequencing Second, epigenetics and transcriptomics Third, systems biology

GWAS: the genetic variants identified often explain 10% of the variation in a trait or disease!

Epigenetics and Transcriptomics Research is increasingly acknowledging that static DNA sequence variation explains only a fraction of the inherited phenotype. Therefore, we expect that multiple epigenetic and gene expression signatures will be related to CVD in experimental and clinical settings.

Complex relationships between the genome, epigenetic and transcriptional regulations, the proteome, and the metabolome that produce CVD phenotypes.

Summary: CHD Relatively common birth defect –4-8/1 000 live births Familial CHD –May not have identical anatomic abnormality Variety of developmental mechanisms –Undergoing revision as we understand molecular pathogenesis

CHD Recurrence risk –If familial, identify inheritance pattern –If not familial, use empiric risk data del22q11.2 is a common cause of CHD –Up to 25% of flow lesions –Flow lesions represent 50% of all CHD –Therefore, 12.5% of all CHD