INFLUENCE OF GENES ON CHILD HEALTH AND DEVELOPMENT

Author:  Tibanyendera Deogratias (BA, /MA Child Psyc/ MPH-Maternal and Newborn Health/ Cert Comm Health/ Dip PPM

The article focuses on the effects of genes to the resultant growth and development of a child.

A gene is a unit of heredity in a living organism. It normally resides on a stretch of Deoxyribonucleic acid –DNA, a self-replicating material present in nearly all living organisms as the main constituent of chromosomes that codes for a type of protein.  All living things depend on genes, as they specify all proteins and functional chains. A gene can also be described as a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the proteins coded directly by genes (APA)
Children’s health includes the study of possible environmental causes of children’s illnesses and disorders, as well as the prevention and treatment of environmentally mediated diseases in children and infants.

Children are highly vulnerable to the negative health consequences associated with many environmental exposures.

What determines how a child develops?

In reality, it would be impossible to account for each and every influence that ultimately determines who a child becomes. Some of the most apparent influences such as genetics, parenting, experiences, friends, family relationships and school to help us understand the influences that help contribute to a child's growth.

Considering how genetic influence can impact on a lifetime health experiences, a factor that is under discussion, I cannot rule out the play of the environment, nutrition, and weather in child health. From the earliest moments of life, the interaction of heredity and the environment works to shape who children are and who they will become. While the genetic instructions a child inherits from his parents may set out a road map for development. The environment can impact how these directions are expressed, shaped or event silenced. In this article I take a look at how genetics and some of the genetic disorders that can impact on child psychology and development.

Growth of cells

To understand genes and their effects, it’s imperative to first know how cells and genes develop right from inception.
At its very beginning, the development of a child starts when the male reproductive cell, or sperm, penetrates the protective outer membrane of the female reproductive cell, or ovum. The sperm and ovum each contain chromosomes that act as a blueprint for human life. The genes contained in these chromosomes are made up of a chemical structure known as DNA (deoxyribonucleic acid) that contains the genetic code, or instructions, that make up all life.

Except for the sperm and ova, all cells in the body contain 46 chromosomes. Hence, the sperm and ova each contains only contain 23 chromosomes. This ensures that when the two cells meet, the resulting new organism has the correct 46 chromosomes. This affirms that life is already determined by the genes fright from formation. If they are the right combination, development will be normal and if they are any anomalies, child development shall be compromised with assuming environmental and others factors remain constant (Everman, David B., and S. B. Cassidy. 2000).

Gene Genotype to Phenotype

A genotype refers to all of the genes that a person has inherited: A person's genotype is the sum total of the genetic material transmitted from his or her parents and the actual expression of these traits is the person's phenotype. A person's phenotype is the observable signs, symptoms, and other aspects of his or her appearance. The term is also used sometimes to refer to a person's outward appearance and behaviour as these results from the interaction between the person's genotype and his or her environment.

The phenotype can include physical traits, such as height and colour or the eyes, as well as nonphysical traits such as shyness, a high strung temperament or a thirst for adventure. While our genotype may represent a blueprint for how children grow up, the way that these building blocks are put together determines how these genes will be expressed. For example even if two children are from same parents with same genotypes, one child may be tall or dark or even big or small but they have the same genotypes.

Behavioural phenotype: The concept of a behavioural phenotype is used most often with reference to patterns of behaviour found in certain developmental disorders of childhood, such as Down syndrome or Prader-Willi syndrome. Behavioural phenotype refers to the greater likelihood that people with a specific genetic syndrome will have certain behavioural or developmental characteristics compared to people who do not have the syndrome; it does not mean that every person diagnosed with a given genetic syndrome will invariably develop these characteristics or it doesn’t necessarily mean that if a parent has asthma, then all the children will all have asthma.

Influences on Gene Expression

Expression of a gene is expressed dependant on two different things: the interaction of the gene with other genes and the continual interaction between the genotype and the environment.

Gene - Environment Interactions: The environment a child is exposed to both in the uterus and throughout the rest of his or her life can also impact how genes are expressed. For example, exposure to harmful drugs while in uterus can have a dramatic impact on later child development. Height is a good example of a genetic trait that can be influenced by environmental factors. While a child's genetic code may provide instructions for tallness, the expression of this height might be suppressed if the child has poor nutrition or a chronic illness.

Genetic causality

At times, genes are not reliable and can go off truck or way off the expected result. Sometimes when a sperm or ovum is formed, the number of chromosomes may divide unevenly, causing the organism to have more or less than the normal 23 chromosomes. When one of these abnormal cells joins with a normal cell, the resulting zygote will have an uneven number of chromosomes. Half of all zygotes that form have more or less than 23 chromosomes, but most of these are spontaneously aborted and never develop into a full-term baby.
In some cases, about 1 in every 200 births, a baby is born with an abnormal number of chromosomes. In every case, the result is some type of syndrome with a set of distinguishing characteristics as explained below.

Mental disorders with organic causes

The two most important examples of mental disorders caused by organic changes or abnormalities in the brain are late-onset Alzheimer's disease and schizophrenia. Both disorders are termed as polygenic, which means that their expression is determined by more than one gene. Another disorder that is much less common is Huntington's disease which is monogenic, or determined by a single gene.

Schizophrenia- First-degree biological relatives of patients with schizophrenia have a 10% risk of developing the disorder, as compared with 1% in the general population. The identical twin of a person with schizophrenia has a 40%–50% risk. Families with a history of schizophrenia indicated the existence of genes related to the disorder on other chromosomes. Chromosome 15 is linked to schizophrenia in European American families as well as some Taiwanese and Portuguese families (Scarmeas, N., J. Brandt, M. Albert, et al - 2003).

Alzheimer's disease- Late-onset Alzheimer's disease is a polygenic disorder a specific form of a gene for Apo- lipoprotein E (apoE4) on human chromosome 19 is a genetic risk factor for late-onset Alzheimer's. People who have the apoE4 gene from one parent have a 50% chance of developing Alzheimer's disease; a 90% chance if they inherited the gene from both parents. They are also likely to develop Alzheimer's disease earlier in life.

Down Syndrome; the most common type of chromosomal disorder is known as trisomy 21, or Down syndrome. In this case, the child has three chromosomes at the site of the 21st chromosomes instead of the normal two. Down syndrome is characterized by facial characteristics including a round face, slanted eyes and a thick tongue. Individuals with Down syndrome may also face other physical problems including heart defects and hearing problems. Nearly all individuals with Down syndrome experience some type of intellectual impairment, but the exact severity can vary dramatically. No matter the severity of the syndrome, early intervention can result in much better outcomes, allowing many people with Down syndrome to care for themselves and gain more independence.

Childhood developmental disorders

Developmental disorders of childhood are another large category of mental disorders caused by alterations in genes or chromosomes.
Fragile X syndrome is the most common inherited form of mental retardation and should be considered in the differential diagnosis of any child with developmental delays, mental retardation, or learning difficulties. The syndrome is caused by a large expansion of a cytosine-guanine-guanine repeat which interferes with normal protein transcription from a gene called the FMR1 gene on the X chromosome. Males with the mutation lack a second normal copy of the gene and are more severely affected than females who have a normal FMR1 gene on their second X chromosome.

An expansion mutation of the cytosine-thymine-guanine triplet causes a potentially life-threatening developmental disorder known as myotonic dystrophy. Repeats of the cytosine-thymine-guanine triplet that is just above the threshold for myotonic dystrophy itself may produce a relatively mild disorder, namely eye cataracts in later life. Within two to three generations, however, the cytosine-thymine-guanine repeats become longer, producing a fatal congenital illness. In addition to developmental disorders of childhood, expansion mutations may also be involved in other psychiatric disorders. Anticipation has been found in some families affected by bipolar disorder and schizophrenia, and may also be present in some forms of autism.

Genomic imprinting - which distinguishes between chromosomes derived from a person's father and those derived from the mother. Prader-Willi syndrome and Angelman syndrome. Both disorders were caused by a deletion on the long arm of chromosome 15 in the very same region, extending from 15q11 to 15q13. Children with Prader-Willi syndrome have severe mental retardation, poor muscle tone, small hands and feet, and a voracious appetite (hyperphagia) that begins in childhood. As a result, they are often obese by adolescence. Children with Angelman syndrome, on the other hand, do not speak, are often hyperactive, and suffer from seizures and sleep disturbances. Children with Prader-Willi syndrome are often quiet in childhood but develop stubborn, aggressive, or impulsive patterns of behaviour as they grow older. The onset of their hyperphagia is often associated with temper tantrums and other behavioural problems. They are typically obsessed with food, frequently hoarding it, stealing it, or stealing money to buy food
Beckwith-Wiedemann syndrome is an overgrowth condition in which patients develop abnormally large bodies. They often have low blood sugar at birth and are at high risk for developing Wilms tumour, a childhood form of kidney cancer. Beckwith-Wiedemann syndrome is caused by several different genetic mutations that affect imprinted genes on chromosome 11p15. One of these imprinted genes governs the production of a growth factor that is responsible for the children's large body size.

Williams syndrome is a genetic disorder that results from a deletion of locus 23 on chromosome 7q11. Children with this syndrome often have an "elf-like" face with short upturned noses and small chins. Their behavioural phenotype includes talkativeness, friendliness, and a willingness to follow strangers. They are also hyperactive and easily distracted from tasks. The personality profile of children with Williams syndrome is so distinctive that many are diagnosed on the basis of the behavioural rather than the physical phenotype.
Obesity; there are potential candidate genes linked to early-onset obesity. These include two loci, one near the OLFM4 gene on chromosome 13, and the other within the HOXB5 gene on chromosome 17.

The first gene appears to raise the odds of early-onset obesity by 22%, while the other raises it by 14%.

Abnormalities of the Sex Chromosomes; The vast majority of new-borns, both boys and girls, have at least one X chromosome. In some cases, about 1 in every 500 births, children are born with either a missing X chromosome or an additional sex chromosome. Klinefelter syndrome, Fragile X syndrome and Turner syndrome are all examples of abnormalities involving the sex chromosomes. Kleinfelter's syndrome is caused by an extra X chromosome and is characterized by a lack of development of the secondary sex characteristics and as well as learning disabilities.

Turner syndrome occurs when only one sex chromosome (the X chromosome) is present. It affects only females and can result in short stature, a "webbed" neck and a lack of secondary sex characteristics. Psychological impairments associated with Turner syndrome include learning disabilities and difficulty recognizing emotions conveyed through facial expressions.

Psychological/behavioural vulnerability in adults

Although it was earlier said that emotional wounds in early childhood were the root cause of anxiety and depressive disorders in later life, inherited vulnerability to these disturbances is also a possible cause. In the past two decades, genetic factors have been shown to influence the likelihood of a person's developing mood disorders or post-traumatic syndromes in adult life. Both genomic imprinting and the phenomenon of anticipation may be present in some families with multigenerational histories of depression. Susceptibility to major depression is governed by several different genes on several different chromosomes. Genetic factors are thought to account for about 40% of a person's risk of depression, with environmental factors and personal temperament accounting for the remaining 60%. With regard to manic depression, twin studies have shown that the twin of a patient diagnosed with manic depression has a 70%–80% chance of developing the disorder.

Post-traumatic syndromes- some persons are more vulnerable than others to developing dissociative and anxiety-related symptoms following a traumatic experience. Vulnerability to trauma is affected by such inherited factors as temperament as well as by family or cultural influences; shy or introverted persons are at greater risk for developing post-traumatic stress disorder (PTSD) than their extroverted or outgoing peers. In addition, twin studies indicate that certain abnormalities in brain hormone levels and brain structure are inherited, and that these increase a person's susceptibility to developing acute stress disorder or PTSD following exposure to trauma.

Anxiety disorders- It has been known for some time that anxiety disorders tend to run in families. The human genome point is said to influence genes in the development of generalized anxiety disorder. It’s said that the heritability of Generalized Anxiety Disorder to be 0.32 chances.

There is a genetic component that may influence the development of agoraphobia, and that it can be separated from susceptibility to panic disorder. Panic disorder is said to be associated with two loci, one on human chromosome 1 and the other on chromosome 11q. The researchers concluded that agoraphobia and Panic Disorder are common, heritable anxiety disorders that share some but not all of their genetic loci for susceptibility.

Child behaviour and temperament - genetic differences among individuals account for approximately 20% to 60% of the variability of temperament within a population. With few exceptions there is no consistent pattern of differential heritability across dimensions to form a wide variety of temperament dimensions including emotionality, activity, shyness, sociability, attention/persistence, approach, adaptability, distress, positive affect and negative affect.  Given that temperament is assumed to be biologically based, it is not surprising to find that parent-rated temperament is genetically influenced. However, genes are dynamic in nature, changing in the quantity and quality of their effects across time and therefore, can be sources of change as well as influencing continuity in behavioural development.  So to say, the role played by genes in development of temperament cannot be measured.

Low IQ and antisocial behaviour; one obvious result is that genetic factors account for the association of low IQ and antisocial behaviour. Antisocial behaviour is partly heritable throughout the lifespan, including in early childhood, particularly if it is pervasive across home. Genetic influences explain about one third of the variation in IQ in young children, and the amount of variance in IQ explained by genetic influences increases through adulthood. A genetically mediated association between low IQ and antisocial behaviour would be consistent with a common neurodevelopmental etiology, as suggested in the model proposed by Nigg and Huang-Pollock (2003). A common genetic etiology also would suggest that some of the genes influencing IQ contribute to variation in antisocial behaviour or vice versa.

Conclusion 

Clearly, genetics have an enormous influence on how a child develops. However, it is important to remember that genetics are just one piece of the intricate puzzle that makes up a child's life. Environmental variables, including parenting, culture, education and social relationships also play a vital role.

References
1.    American Psychiatric Association (2000). Diagnostic and Statistical Manual of Mental Disorders. 4th edition, text revised. Washington, DC: American Psychiatric Association.
2.    Everman, David B., and S. B. Cassidy (2000). "Genetics of Childhood Disorders: XII. Genomic Imprinting: Breaking the Rules." Journal of the American Academy of Child and Adolescent Psychiatry 39: pp 445-448.
3.    Faraone, Stephen B.et al (1999). Genetics of Mental Disorders: A Guide for Students, Clinicians and Researchers. New York: The Guilford Press.
4.    Nigg JT, Huang-Pollock CL. (2003). The causes of conduct disorder and serious juvenile delinquency. New York: Guilford Press; pp. 227–253.
5.    Scarmeas, N., J. Brandt, M. Albert, et al (2003). "Association Between the APOE Genotype and Psychopathologic Symptoms in Alzheimer's Disease." Neurology 58: 1182-1188.