“It’s all in the genes!” You may have heard your parents proudly say when you were complimented as a child on your physical attributes or on your academic achievements. But when it comes to heredity, it isn’t just about the genes. Chromosomes play a significant role too according to Pre-implantation Genetic Testing Scientist Mr Aaron Chen.
Genes vs chromosomes
Delving into the subject of genes and chromosomes, Aaron says, “Genes are basically the instructions for building and maintaining our bodies whereas chromosomes are chains which are formed from these genes during cell division. Each cell in our body contains 46 chromosomes with each chromosome consisting of thousands of genes. Hence, a normal person would have roughly 25,000 genes.”
“An individual may have a normal number of chromosomes but can still experience mutation on one or more genes on their chromosomes. In that case, they will have what is called a genetic disorder. Similarly, someone may have normal genes but can have an abnormality in one or more of their chromosomes. Should that happen, they have a chromosomal disorder,” Aaron explains when asked about the difference between chromosomal and genetic disorders. “Many people clump them under ‘genetic conditions’ but they are actually two different things.”
Here’s a rundown on some genetic and chromosomal disorders commonly found among Malaysian children.
This disorder is passed on in an autosomal recessive pattern, meaning both copies of the gene in the child’s every cell are mutated. For the child to be affected, both parents must be carriers. Every kid has a 25% risk of being affected. They usually suffer from reproduction and digestion complications, and recurring lung infections – a result of their bodies producing excessive thick, sticky mucus.
Inherited blood disorders like thalassaemia prevent red blood cells (RBCs) from properly producing haemoglobin (an oxygen-transporting molecule). This subsequently causes anaemia which gives off symptoms like jaundice, diarrhoea, an enlarged spleen and heart, breathlessness and brittle bones.
Sickle cell anaemia, another blood disorder gives RBCs a crescent shape, instead of its normal disc shape. Kids with this condition are prone to infections, tissue damage and stroke.
Delayed development, seizures, eczema, behavioural and motor complications are common among children with phenylketonuria as their livers are incapable of producing an enzyme to metabolise phenylalanine. High levels of this amino acid harm the brain.
Caused by an additional gene copy on chromosome 21, this disorder produces symptoms normally noticeable at birth like diminished muscle tone, heart defects, protruding tongue, thick lips and flat nose. Symptom severity can vary among children.
A normal cell has two sex chromosomes (males have one X chromosome and Y chromosome while females have two X chromosomes) but people with Turner syndrome only have one normal X chromosome; the other is either structurally changed or absent. Therefore, Turner syndrome only strikes in females. Sexual development in these females is impaired; most are infertile and some don’t undergo puberty unless treated with hormone therapy.
Fragile X syndrome
Linked to the common forms of inherited mental retardation and developmental delays like autism, hyperactivity and attention deficit disorder (ADD), this condition arises when a portion of the X chromosome breaks apart – hence, its name ‘fragile X.’ The portion, which induces the fragility, may be repeated on the chromosome; the more repeated portions, the higher the fragility and the more severe the syndrome.
1. Active Beat. Available at www.activebeat.com/your-health/children/the-10-most-common-genetics-disorders/6/
2. Education.com. Available at www.education.com/reference/article/chromosomal-genetic-disorders/
3. Genetics Home Reference. Available at http//ghr.nlm.nih.gov/condition/fragile-x-syndrome
4. Seattle PI. Available at http://education.seattlepi.com/difference-between-genetic-defect-chromosomal-abnormality-4617.html
5. Steady Health. Available at www.steadyhealth.com/articles/the-16-most-common-genetic-diseases