Inherited metabolic disorders are rare genetic diseases that result in metabolism problems and while they affect small numbers of people, they have a very big impact – especially when children in particular are not diagnosed or diagnosed late.
Being so rare, doctors do not see these disorders often (or at all), so they can be missed. Some are treatable, improving quality of life, so the importance of an early diagnosis cannot be underestimated.
What causes an inherited metabolic disorder?
These disorders are often due to defects of a single gene that codes for enzymes that help the body convert various substances into other products. Problems can occur due to an accumulation of substances which are toxic or interfere with normal function, or because the body, without the necessary enzyme working properly, cannot synthesise essential compounds.
Global Developmental Delay (GDD)
Many inherited metabolic disorders lead to Global Developmental Delay (GDD) - when a child takes longer to reach certain development milestones than other children their age – so whilst some are diagnosed at birth, often it is only later that the problem is discovered. These milestones might include learning to walk or talk, movement skills, learning new things and interacting with others socially and emotionally.
Issues in diagnosis
Often a key factor in making a diagnosis of an inherited metabolic disorder is a decline or stalling in function as the damage begins to take effect and increases. Unlike a brain injury which causes cerebral palsy, or a chromosomal condition like Down’s syndrome, the effect of an inherited metabolic disorder is cumulative. Some can be diagnosed by a blood or urine test, and others by ruling out other causes, and investigations such as magnetic resonance spectrograph.
Simon Towler, a specialist medical negligence lawyer at Shoosmiths in Northampton, is currently acting for the families of two children with inherited metabolic disorders.
Case study one
The first involves a delay of four years in diagnosing a case of argininosuccinic aciduria, an inherited disorder that causes ammonia to accumulate in the blood, in a girl who is now 12. Usually evident in the first few days of life, an infant with argininosuccinic aciduria may be lethargic or unwilling to eat and have poorly controlled breathing rate or body temperature. The condition can be diagnosed via blood and urine tests.
In this case, the condition was classed as moderate, so was missed at birth, but should have been picked up when developmental milestones were not reached. An amicable settlement is being reached, to reflect that, without treatment, the youngster’s quality of life as well as her ability to interact with her family and enjoy physical activity was reduced. Simon notes that as soon as his young client started to have the treatment, her vocabulary, her enthusiasm, her activity levels, and her balance all improved.
Case study two
The second case concerns Guanidinoacetate methyltransferase (GAMT) deficiency, an inherited disease that affects the brain and muscles. People with this disease may begin showing symptoms from early infancy to age three. Signs and symptoms can vary but may include mild to severe intellectual disability, recurrent seizures (epilepsy), problems with speech, and involuntary movements. People with this disease may also have behavioural problems, including hyperactivity, autistic behaviours.
With GAMT deficiency the body does not receive enough creatine, so the parts of the body that use a lot of energy, such as the brain and muscles, do not work properly. Treatment with supplements of creatine monohydrate can be very effective but needs to be administered early. In this case, the diagnosis should have been made at around two but was in fact made at age 18 by chance when the child was enrolled on a genetic study. With more timely treatment, this youngster’s condition would be much improved, as would her quality of life.
“More and more of these metabolic disorders are being discovered, and some are treatable. At the very least, with a timely diagnosis you would know what was going on. If your first child has this problem, then if they so choose, parents would be able to seek counselling about having a second.”