Fatty acid supplementation in a case of maternal phenylketonuria

Currently, since many women with phenylketonuria (PKU: McKusick 261600) are of childbearing age, maternal PKU represents a new clinical challenge. Many studies have demonstrated a significant correlation between phenylalanine (phe) plasma levels during gestation and risk for embryo fetal abnormalities (Lenke and Levy 1980). Therefore, the first problem to deal with is to put PKU women on a strict low-phenylalanine dietary regimen, which can be effective only if started before conception, to be continued until delivery. Such an exclusion diet, aimed to maintain plasma phe concentration between 120 and 360#mol/L, could itself cause some abnormalities to the offspring as a result of secondary nutritional deficiencies, as suggested by some experimental data. We previously reported (Galli et al 1991) low plasma levels of long-chain polyunsaturated (LCP) fatty acids (FA) of both n - 6 and n - 3 families in treated PKU patients. These compounds, contained preformed only in whole animal foods, play a key role in central nervous system development from the 6th month of gestation fo the 3rd month of extrauterine life. A selective accumulation of both n - 6 and n - 3 LCPFA in fetal nervous tissues during the third trimester of gestation has been shown (Clandinin et al 1980). We report here the case of a 29-year-old woman, C.I., who was diagnosed as affected by classical PKU at 9 months of age (plasma phe 1200 #mol/L). A low-phe diet was soon introduced, achieving good metabolic control and normal psychomotor development. At the age of 9 years, her diet was interrupted on her parents' decision, against our advice. At 27 years, she married a healthy man and, after referring to us, programmed her pregnancy in order to reintroduce dietary treatment 12 months before conception. Her plasma phe level dropped from 1200/~mol/L to 120 #mol/L, remaining stable throughout gestation. At 5 months gestational age, a blood sample was drawn after an overnight fast to measure nutritional indexes, including her plasma FA status. Lipids were extracted with chloroform methanol (Folch) and FA methyl esters were analysed with a 4160 Carlo Ekba gas chromatograph equipped with Supelcowax 10 capillary column. The FA pattern of plasma total lipids (FA expressed as weight percentage of total FA) was compared with that of 9 healthy women (23-34 years) at the beginning of the third trimester of pregnancy (mean + SD). Values lower than 2SD of the mean control were found for c~-linolenic acid (18 : 3 n - 3, 0.07 vs 0.42 _+ 0.15), eicosapentaenoic acid (20:5 n-3, 0.14 vs 0.56 + 0.18) and docosahexaenoic acid (22:6 n- 3, 0.49 vs 0.92 _ 0.21). Differences that were not significant were found for linoleic acid (18 : 2 n - 6, 29.5 vs 27.9 + 9.6) and arachidonic acid (20:4 n - 6, 4.52 vs 6.20 ± 2.85). To provide our patient with a sufficient intake of the deficient n - 3 compounds (whose dietary need was calculated as 0.5% of total daily calories), we supplemented her diet with fish and blackcurrant oils in pearls, daily providing 240 mg 18 : 3 n - 3, 60rag stearidonic acid (18:4 n-3), 360rag 20:5 n-3 and 240rag 22:6 n- 3. Blackcurrant oil also contains sufficient 7-1inolenic acid (18:3 n - 6), important for a better metabolic balance between the two major polyunsaturated series. After 1 month, the plasma FA pattern averaged control values both for precursors and derivatives of the two series (18:2 n- 6, 26.2; 18:3 n- 3, 0.54; 20:4 n- 6, 5.94; 20:5 n - 3, 0.62; 22:6 n - 3, 1.04). She continued to be supplemented with LCPFA until delivery. Her male offspring was clinically normal (weight, length and head circumference on 50th centile) as is his subsequent psychomotor development. In conclusion, we observed the normalization of the plasma FA pattern in a case of an LCPFA-supplemented pregnant PKU woman. It is to be hoped that multicentric matched case-control studies will address the functional effects of this type of nutritional intervention on the offspring