The three children who emerged from an Austrian cellar last week are showing clear physical signs of their years spent underground.
The children never saw sunlight
While the resilience of children cannot be underestimated, the effects of a sunless prison on their developing bodies could be long lasting.
The actions of Josef Fritzl meant that neither his daughter, Elisabeth, nor her imprisoned children, had any access to modern healthcare, or even sunlight.
Pregnancy and childbirth would have been the time of greatest risk.
Maternal death rates in Europe are approximately a hundredfold less compared with parts of the world where there is poor or non-existent antenatal and postnatal care - analogous to the situation faced by Elisabeth.
The risk to her newborn children was also substantially increased by the lack of proper facilities.
It is not known whether the life of her seventh child, a twin baby who died shortly after birth, could have been saved if medical care had been at hand.
However, Patrick O'Brien, a spokesman for the Royal College of Obstetricians and Gynaecologists, said it was reasonable to suggest a massive increase in risk for Elisabeth during this time.
"Most babies will be delivered absolutely fine, even without medical assistance, but there is a huge rise in the chance of serious complications for both mother and baby when there is a lack of care during pregnancy, and particularly around the time of birth.
"This is particularly so during twin deliveries."
None had seen a doctor or a dentist since birth, and it is reported that, at the age of 19, the oldest daughter kept in captivity has already lost most of her teeth.
The cellar had no windows, and a lack of sunlight can be harmful - it helps the body produce vitamin D, which has a role in bone formation.
The children have been treated in hospital
While a healthy diet can compensate for this, there are signs this was not the case for these children, with medical tests revealing vitamin D deficiency.
The consequences are unclear, but there is some evidence to suggest that vitamin D may help to prevent diseases such as cancer, diabetes, tuberculosis and heart disease.
Vitamin D deficiency can cause pain, spasms and weakness in the muscles. It can also cause joint pain, soft and deformed bones and retarded growth.
Another problem for the older children is directly related to the low ceilings in their prison - a permanently hunched posture.
Other long term effects are less clear, although the authorities suggest that the children have "defective" immune systems.
The development of a healthy immune system does depend to some extent on the body being constantly challenged by new infections and allergens, and a childhood spent in virtual isolation would prevent this from happening.
Professor Bobby Gaspar, a specialist in paediatric immunology at Great Ormond Street Hospital in London, said the information released by the Austrian authorities did not reveal much about the precise nature of the immune problem, and that the true extent of this would become clear over the coming months.
He said: "A healthy immune system isn't just created by nature, but also by the environment that a child lives in - there could be a lack of exposure to the normal repertoire of challenges that other children would face."
He suggested the children's immune system might also be compromised in some way by lack of vitamin D, which plays a key role in enabling immune cells to clear the body of potentially harmful debris and infection.
If their immune systems are permanently damaged by their captivity, then they could face a lifetime of increased vulnerability to a range of infections and illnesses.
Otherwise, say the Austrian authorities, the children are healthy, and it appears that most of the six fathered by Fritzl have escaped the threat of genetic defects caused by inbreeding.
Quite apart from the social stigma associated with incestuous relationships, there is good biological reason why they are a very bad idea.
If a family harbours a genetic defect, there is a raised risk that a child of an incestuous relationship could inherit two, rather than one copy of the defective gene, making a health problem inevitable.
One of the three children raised in the rooms above is reported to have a heart defect, but it is unknown whether this could be the result of a genetic problem.
There is little or no data about the threat of this from relationships between father and daughter, although in rough terms, the risk of defects is doubled in first cousin marriages.