"I have seen many dogs in my life that were small and slow growing up but later they recovered. However, one pup of my dog has had a prolonged growth and unable to participate in games actively. Could this be a genetic disorder like Down Syndrome?" – Shavin, a question from the forums.
This is a really interesting topic Shavin, and something that I expect any breeder or new puppy owner will be interested to know.
Genetic conditions are always a worry when it comes to breeding puppies. They can happen for two reasons; either when the embryo was developing, there was a chance mutation in the DNA, which has resulted in abnormal development in one way or another, or it can be because both parents were carriers of a recessive gene unknowingly.
Genetics are complicated, however, to put it simply, every animal has two sets of genes (also known as chromosomes); one from the father and one from the mother. Genes can either be dominant or recessive, which means that if the gene is dominant, it will cause the condition to be noticeable even if both genes are not the same. Whereas if it is recessive, both genes must be the defective gene to cause the visible condition. As an example, a parent of a puppy might have one normal gene (N) and one defective recessive gene (D). This would make her what is known as a carrier. She would not have the condition visibly, but she has the potential to produce offspring who would have it. So, if two carriers (ND) mate, the four possible outcomes of their offspring would be NN (normal), ND (carrier), ND (carrier) or DD (condition), i.e. a 25% chance that the puppy would have the condition. This means that it is easy to unknowingly breed dogs with defective genes for many generations before the condition is evident.
Now, coming to your question about Down Syndrome. Down Syndrome is when a human has a third copy of chromosome 21, rather than a pair, but humans have 23 pairs of chromosomes, whereas dogs have 39 pairs of chromosomes. Therefore, the DNA that makes up chromosome 21 in dogs is very different from that which makes up chromosome 21 in humans. If a dog was to have three copies of chromosome 21, it would not present like Down Syndrome would in humans.
With that being said, there are many conditions which are very similar to Down Syndrome which we see in dogs, and two spring to mind which would fit the symptoms you are describing.
The first is Pituitary Dwarfism, which leads to significantly stunted growth, as well as an occasionally increased pigment in their skin and coat, and hair loss. This is a recessive gene which causes the pituitary to produce less growth hormone (GH). The lack of GH also means that the thyroid does not develop properly, leading to dullness and slow intelligence.
The second is Hypothyroidism. This can be a genetic or acquired condition, which leads to the thyroid gland underproducing triiodothyronine (T3) and thyroxine (T4), or not responding to thyroid stimulating hormone (TSH). As a result, the dog will be mentally impaired, dull and prone to putting on weight. In addition to this, the legs and spine are usually shorter, leading to an apparent stunted look.
I hope this has been helpful, and I’d just like to close with one comment; I always recommend that any dog who is not developing appropriately should be taken to the vet for a check over. They will be able to give a definitive diagnosis and appropriate treatment, which is important for your puppy to have a lovely long, healthy life. Good luck!