Senior Metabolic Dietitian
Biochemical Genetics Program, Waisman Center
University of Wisconsin-Madison
The Biochemical Genetics Program at the University of Wisconsin in Madison has followed 6 pregnancies in women with MSUD (3 mothers – 2 with classical MSUD and one with variant MSUD – each mother has had 2 children). We are currently following another woman who is in her second trimester. There have been reports of a couple other pregnancies in those with MSUD, but experience is still limited and the metabolic community needs to continue to learn more about pregnancies in this disorder (1-3).
At this time, we do not have enough information to determine if leucine or the other branch chain amino acids are teratogens when levels are higher than normal. Teratogens are compounds that, when ingested by a pregnant woman, can have adverse effects on her developing fetus. Commonly known teratogens include alcohol and various drugs that can have devastating effects on an infant’s outcome. In metabolics, we know most about the teratogenic effects of phenylalanine (phe), the amino acid that cannot be metabolized in PKU. Pregnancies in PKU have been well studied and it is clear that elevated phe levels during pregnancy can cause microcephaly (small head size), developmental delay and congenital defects.
We do not know if leucine is a teratogen. In our pregnancies and the few that have been reported, infant outcome appears to be good. BUT, our women were on diet before pregnancy, and continued diet treatment throughout pregnancy, and maintained normal blood leucine levels. So we really can’t say if the infant outcome would be different if this had not been the case.
Women with MSUD who are pregnant continue to be at risk for metabolic episodes associated with illness or poor intake. Pregnancy does not reduce this risk. The first trimester has been especially difficult for some of our women because of morning sickness. The nausea and vomiting associated with morning sickness can make it difficult for a woman to take sufficient calories and protein from formula. This can lead to metabolic decompensation, just as it can with women with MSUD who are not pregnant.
Another time that we have found that women are especially vulnerable to metabolic decompensation is during delivery and the post delivery period. After delivery, a woman begins to “break-down” protein stores as the body changes from pregnancy metabolism to post-pregnancy metabolism. We have found that it is imperative that a woman follow her diet and continue to be monitored for a minimum of 2 weeks after delivery to prevent a metabolic episode. The importance of continuing diet after delivery was especially evident in a research report from Japan published in 2003. This woman was not very compliant with diet treatment during pregnancy, but stopped treatment after delivery. This woman died 51 days after delivery (3). This clearly shows the importance of diet management during and after a pregnancy in MSUD.
There are women with mild forms of MSUD that who may not require strict diet treatment as an adult and have few, if any, metabolic episodes. BUT, pregnancy is a big stress on metabolism as is the post-pregnancy period. So, even if a woman does not have problems associated with MSUD when she is not pregnant, this does not guarantee that she would not have problems during a pregnancy. Any woman with MSUD, no matter how mild it may be, should be followed by a metabolic clinic before pregnancy to assure good metabolic control and continue to be followed during and after her pregnancy. All of our women have been referred to a high-risk obstetrics clinic for more extensive monitoring of the mother and her developing fetus.
- Van Calcar SC, Harding CO, Davidson SR, Barness LA, Wolff JA (1992) Case reports of successful pregnancy in women with maple syrup urine disease and propionic acidemia. Am J Med Genet 44: 641-646.
- Grunewald S, Hinrichs F, Wendel U (1998) Pregnancy in a woman with maple syrup urine disease. J Inherit Metab Dis 21: 89-94.
- Yoshida S, Tanaka T (2003) Postpartum death with maple syrup urine disease. Inter J Gynecol Obstetrics 81: 57-58.