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New Treatments for Biochemical Disorders

Biochemical disorders are caused by genetically determined defects, usually in an enzyme, although sometimes they are in receptors or other parts of the pathway. Unfortunately sometimes the body makes toxic substances. In the case of PKU, the body makes phenylactate.

How do inborn errors present? They present a number of different ways. They can present acutely as metabolic disease of the newborn. This is when you have a child that looks like he has sepsis. You give him antibiotics and he does not get better. They can be progressive disorders which present with gradual organomegaly, loss of milestones.

There are so many metabolic diseases but in most states in the United States only three are screened for in the newborn period. These are PKU, galactosemia, and hypothyroidism. Why just those three? Why don’t we screen for pipecolic aciduria? Well, they are very rare. That’s one reason. Another reason is that there is not a darn thing you can do about it, and the third reason is there is no cheap screening test. So these are the principles that we have to deal with. First of all, it must be a serious disease. It has to be preventable or treatable.

PKU is the most common amino acid disorder. The screening test is very simply measuring phenylalanine from a blood spot on a newborn screening card from a heel stick. There’s a prerequisite. Children have to have taken in protein in the form of formula for at least 24 hours. If not, you’ll have a false negative. And in these days of early discharge from the hospital where kids barely get a little glucose to suck on, it’s very important to bring them back in the first few days of life to their primary care provider to get an adequate specimen, meeting the prerequisite. The diagnostic test is to do a quantitative plasma amino acid profile.

Homocystinuria is very uncommon, compared to PKU, and the screening test in those states that do it is not to measure homocystine, because it’s a little difficult - because it’s an unstable compound - they actually measure methionine. The diagnostic test is to do a complete plasma amino acid profile. I’ll stress again, nobody gets urine amino acids anymore.

How do we treat these kids? For the most part we don’t really treat them with dietary restriction of protein or methionine anymore. But rather we supplement them with either folate.

Normally there is zero homocystine in the plasma. So this is easy to make the diagnosis, as long as the sample gets to the lab properly. It has to be placed on ice and has to be spun down within an hour or two. Because this is an unstable compound and if you let it sit out.

Metabolic diseases of the newborn. We are talking about 1:10,000, 1:100,000. So individually all these disorders are rare, but you put them all together and they are a formidable enemy and have to be dealt with, and suspected.

Hyperammonemia. There are many causes of hyperammonemia. It may have to do with immaturity of the hepatic enzymes. But it goes away. It doesn’t mean that it might not need to be treated before it goes away. Urea cycle disorders certainly scare us all to death and have, on occasion, really ruined a weekend for me.

Tay-Sachs. The incidence used to be about 1:4,000 among Ashkenazi Jews because the carrier frequency is quite high. The screening test is to measure hexosaminidase A in the serum, and the clinical features you must be familiar with. Hyperacusis, or increased startle reflex, progressive weakness or hypotonia, visual loss, the cherry red macula, macrocephaly and usually early

There was a treatment touted a few years ago, something called Lorenzo’s oil, which is a dietary supplement consisting of monounsaturated long chain fatty acids. The theory here was to decrease the amount of very long chain fatty acids by putting in not quite so long chain fatty acids into the diet and making them monounsaturated so they have a single double bond here. This

There are some metabolic diseases we can do something about: PKU and a low phenylalanine, low-protein diets. You give them just enough proteins so that these patients can grow. Homocystinuria: we used to decrease their protein restriction a little bit but now betaine has sort of taken care of all of that, and we usually don’t restrict the diet in kids with

We also have some pharmacologic weaponry to fight some of these disorders:  betaine in homocystinuria, the ammonia scavengers, sodium benzoate and phenyl acetate, phenylbutyrate for urea cycle disorders. Many patients with MSUD are responsive to thiamin. Some of

The successful management of inborn errors has many components to it. Early detection is the key. You can’t treat these diseases until you diagnose them. So you must have an index of suspicion. You have to educate the family, especially if there is a special diet involved or special medications involved, they must be compliant. The need financial and social support. If the

In terms of Hurler’s, the diagnostic test is to measure the enzyme iduronidase, which can be measured in blood as well as from a skin fibroblast cell line. The clinical features: progressive, coarse facial features. So-called gargoylism. Corneal clouding, loss of milestones, severe mental retardation, hepatosplenomegaly, hirsutism, hernias and these multiple bony changes. So dysostosis multiplex. Complications include recurrent pneumonia because of thick secretions, congestive heart failure because of valvular involvement, and in the case of Hurler’s, usually

The mucopolysaccharidoses present sometimes with growth delay, with organomegaly, corneal clouding, joint stiffness. The more severe manifestations include hirsutism or increased body hair, loss of milestones and these