Biological and Genetic Influences on Children’s Development

The Human Genome Project was finished in 2003, and the first complete sequencing of DNA in a human cell was made available to the public for review. Until recently, little was known about genes contributing to neurodevelopmental problems from the research of single gene mutations, impairing the standard action of a single gene.

Disorders caused by defects in a single gene are sporadic (usually with a frequency of less than 1 in 10,000). Remarkable progress is being made in our knowledge of the aetiology of single gene disorders like Fragile X or Rett syndrome, and novel therapeutic options are being identified that may have broader implications.

How Many Genes are There?

Humans contain roughly 19 000 protein-coding genes [significantly fewer than the estimated 120 000 predicted ten years ago]. We have roughly the same amount of genes as a mouse and far fewer than rice plants. Human DNA contains information in the form of long sequences of nucleotides. The bases adenine, guanine, thymine, and cytosine are joined with a sugar molecule (deoxyribose in DNA) connected to a phosphate group to form nucleotides.

The letters A, G, T, and C are commonly used to represent these bases. A DNA strand's nucleotides are organized in pairs. The human genome contains around 3 billion nucleotide pairs per haploid set of chromosomes. We generally have 23 pairs of chromosomes, and each pair member is identical in females. In men, one of the sex chromosomes is a Y rather than an X, but the total number remains the same (46 for the whole diploid set). The DNA double helix is tightly coiled to fit massive amounts of information inside a cell nucleus.

Recent research has focused on how that coiling happens, what laws govern it, and how the equipment that wants to read the DNA sequence, produce proteins, and regulate cellular activity has access to it.

Reading the entire sequence of our DNA for the first time was a huge accomplishment. Assume that each nucleotide is the size of a 1-cent piece in the United States or a one-new penny piece in the United Kingdom; both have a diameter of roughly 2 cm. This, of course, dramatically increases the size of each nucleotide from its actual dimensions. If 3 billion pennies were set side by side, they would span nearly 35 000 miles, which is greater than the diameter of the Earth at the equator (25 000 miles).

Sources of Genomic Variation

The cell's genetic machinery reads nucleotides in triplets, from left to right, in any depiction (e.g., AAA, CCC, TTA, ATG). Each triplet may code for an amino acid or signal (e.g., start, stop) or have no value. Until recently, we assumed that the primary reason people (of the same gender) varied was due to minor differences in the usual nucleotide sequence of their DNA. These variations are known as single-nucleotide polymorphisms (SNPs).

Our DNA sequence of nucleotides is remarkably identical from person to person, with just around 0.4% of our genome varying owing to SNPs. Nucleotide substitutions occur once every 800 bases (nucleotide) pairs on average. Suppose the change in our nucleotide sequence (e.g.,...TCTGATTG... becoming...ACTGATTG... ) happens in a genetic coding or regulatory region.

In that case, it may affect gene expression or the protein structure eventually generated from the gene in question. Alternatively, the replacement might have silent implications. If such changes in gene sequence are relatively prevalent, we call them polymorphisms. Polymorphisms are defined as occurring in more than 1% of the population. The genetic background of the researched population substantially affects the occurrence of polymorphisms. For example, this implies that their distribution may differ significantly between African and European Americans.

Other causes of genetic variation exist as well. These include small-number nucleotide insertions, deletions (indels), and more significant structural rearrangements within or across chromosomes (typically detectable by microscopy). Copy-number variations (CNVs) occur when these indels are particularly substantial (more than 1000 base pairs) and cause an increase or reduction in the number of copies of a single gene or a series of genes.

Increasing or lowering the number of copies of specific genes can affect susceptibility to various diseases. Several large-scale investigations of autism and schizophrenia, for example, have found that specific CNVs are substantially more frequent in both diseases than in control groups.

Until recently, copy-number variations were not recognized as significant risk factors. They are more likely to be pathogenic if made up of deletions rather than insertions of DNA sequences. They can be inherited or develop spontaneously. Their discovery has challenged mental genetics methodologies and opened up a new research arena. These CNVs may account for as much genetic risk as SNP variation.

Determining the significance of a copy number variation for gene function is difficult since they, by definition, interrupt long DNA sequences. Identically positioned CNVs in multiple major mental illnesses show that the genes have not read the textbooks that precisely define diagnostic categorization.

Mechanisms of Genomic Regulation

Technological advances provide fresh insights into the ramifications of individual variances in DNA sequences. Every human cell has a lot of DNA but fewer genes than we expected. Most human DNA is similar, but as we have shown, the diversity that does occur can have substantial implications for illness prediction, prevention, diagnosis, and therapy.

Surprisingly, maybe, we are confronted with a slew of unanticipated and quickly growing issues surrounding how we identify genes and how they are regulated. We used to believe that a gene was a fragment of DNA in the cell nucleus that coded for a protein and that protein creation was handled by RNA, which read the genetic material and delivered the code to protein-building machinery on the ribosome, which was located elsewhere in the cell. In recent years, we have found many more types of RNA than we previously thought and an incredibly complicated regulatory apparatus.

Genomic regulation is now recognized to include a variety of interactions between proteins and RNA molecules, some of which can result in RNA changes; over the next several that, our understanding of the role of tiny RNA molecules, which are crucial in this process, will vastly improve. They are, incidentally, being found at a rapid speed. We are unlikely to be able to construct illness models using the information acquired from the entire DNA sequence in a human genome unless we understand how individual differences in gene regulation lead to diseases. A few triplets of DNA nucleotides do not elevate the risk of mental disease.


We are getting better at measuring human genetic variation. The cost of giving us a map of our genome is fast declining. When such information becomes available, it will signal the end of an era in which the focus has been on genetic sequencing and the start of a new period in which the functional activity of that genome takes centre stage.

The realm of '-omics,' as illustrated by genomes, transcriptomics, proteomics, epigenomics, and so on, will inevitably impact every element of medical science. Finally, it will impact the assessment and treatment of all illnesses addressed in this volume: Being forewarned is being forearmed.

Updated on: 10-May-2023


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