A mother-of-two has shared the subtle warning sign that lead to both of her children being diagnosed with a rare type of childhood dementia. 

Megan Kempf, 37, from Illinois, had a completely normal pregnancy and she and her husband, Kyle, were so excited to welcome their baby girl, Poppy, into the world. 

But after three normal years, the stay-at-home mother began to wonder if her daughter was somehow different to her peers. 

She said: 'We had noticed that her drawing skills had regressed; she would be able to draw bodied characters, and suddenly she'd regressed to drawing circles.' 

When Poppy, now 9, started school, her differences became more pronounced and she was diagnosed with mild intellectual disability - which involves slower development in thinking, social and processing skills.

But her parents felt there was still more to uncover, as Poppy became increasingly anxious around bedtime. 

'We started to investigate more things, and found that Poppy had sleep apnoea,' Megan said. 

Sleep apnoea occurs when a person's breathing stops and starts while they're sleeping and can make it very hard to concentrate during the day. The condition can also cause mood swings, fatigue and headaches. 

'I was concerned that her sleep apnea was maybe exacerbating her delays,' Megan added, 'but nothing was super identifiable or severe so we were being told to wait and see. 

Finally, a neurologist referred the family to a geneticist - a doctor who specialises in diagnosing genetic disorders and conditions such as learning difficulties associated with other problems, familial cancers and chromosomal abnormalities. 

Recalling the life-changing appointment, Megan said: 'We had Poppy's entire DNA genome sequencing, and that came back testing positive for Sanfilippo syndrome type B.'  

Sanfilippo syndrome is a rare type of childhood dementia - a memory robbing condition caused by more than 145 rare genetic disorders which are progressive and life limiting. 

While these conditions are extremely rare, there is a commonality that they cause dementia in children. Whilst in some cases symptoms can present in babies and young children, on others that may not appear until teenage years. 

In Poppy's case, she was just three when her parents began to notice some of the little-known but tell-tale signs of the devastating condition, including a loss of motor skills. 

The rare disease which eventually causes fatal brain damage is caused by a lack of an enzyme that normally breaks down and recycles a large molecule called heparan sulphate. 

Without this gene, the molecule builds up and stops cells from working properly. 

Over time, brain cells fill up with waste that the body is unable to process, triggering hyperactivity, disordered sleep, loss of speech, cognitive decline, seizures, and eventually death. 

'At that moment, we realised, as it is genetic, that we needed to get our son, Oliver, tested too,' Megan continued. 

'Three weeks later, we were told that Oliver, aged 2, had tested positive too.

'To have a diagnosis provided a sense of relief, but never in a million years did we expect to get a life expectancy for our children. 

'We were told most children with Sanfilippo syndrome type B don't survive past 19, and that there was nothing the doctors could do. 

'Poppy is nine - she is halfway there. We were given clinical guidelines, and they told us we were going to qualify for Make-A-Wish and told to make the best time with our kids.

'We were not going to be okay with that.'  

Determined not to give up and find a treatment to save their children, the couple have so far raised $5.5million along with other families for enzyme replacement therapy.

Whist the drug has not yet been approved by the Food and Drink Administration (FDA), the Cure Sanfilippo Foundation believe enzyme replacement therapy is a promising treatment option. 

Megan added: 'We are hopeful that the drugs will be on the market next year, but it will take a lot of attention and effort to get there.

'It is hard to get a rare disease to market, and if it's a paediatric disease, your patient doesn't live long. We mostly want there to be an answer for all these children.' 

According to the Society for Mucopolysaccharide Diseases (MPS Society), a charity which supports children living with Sanfilippo Syndrome, around 140 children in the UK have the life-threatening condition.