IgE in unselected like-sexed monozygotic and dizygotic twins at birth and at 6 to 9 years of age: high but dissimilar genetic influence on IgE levels.

BACKGROUND: IgE is a major determinant of allergic disease. Twin analysis of serum levels of IgE has been carried out previously in children and adults with heritability estimates of 30% to 70% on the basis of ANOVA. OBJECTIVE: This study included the analysis of serum IgE in a population of 126 twins, 27 monozygotic pairs and 36 dizygotic pairs, studied at birth (cord blood [CB] IgE) and consecutively at the age of 6 to 9 years of age (serum IgE). METHODS: IgE was determined by means of RIA. ANOVA, correlation analysis, and structural equation modeling by maximal likelihood analysis was used for genetic analysis. RESULTS: Structural equation modeling by maximal likelihood analysis showed the best-fitting model to be the AE model (A for additive genetic variance and E for environmental variance) both at birth and later in childhood. The estimated heritability was 0.92 (95% CI, 0.84-0.95) for CB IgE and 0.78 (95% CI, 0.60-0.87) for serum IgE. The correlation between CB IgE and serum IgE was 0.04. CONCLUSIONS: The study demonstrated a higher genetic dependency of serum IgE than previously recognized. The low correlation between the IgE levels at birth and later in childhood suggested that different effector mechanisms may be operating at different ages.

Comparison of a partially hydrolyzed infant formula with two extensively hydrolyzed formulas for allergy prevention: a prospective, randomized study.

The aim of this study was to compare the allergy-preventive effect of a partially hydrolyzed formula with two extensively hydrolyzed formulas, in infants with a high risk for development of allergic disease. High-risk infants from four Danish centres were included in the period from June 1994 to July 1995. Five-hundred and ninety-five high-risk infants were identified. High-risk infants were defined as having biparental atopy, or a single atopic first-degree relative combined with cord blood immunoglobulin E (IgE)> or =0.3 kU/l. At birth all infants were randomized to one of three different blinded formulas. All mothers had unrestricted diets during pregnancy and lactation and were encouraged to breast-feed exclusively. If breast-feeding was insufficient, one of the three formulas, according to randomization, was given during the first 4 months. It was recommended not to introduce cow's milk, cow's milk products. and solid foods until the age of 4 months. After the age of 4 months a normal unrestricted diet and conventional cow's milk-based formula were given when needed. All infants were followed-up prospectively with interview and physical examination at the age of 6, 12, and 18 months, and if any possible atopic symptoms were reported. If food allergy was suspected, controlled elimination/challenge procedures were performed in a hospital setting. Of 550 infants included in the study, 514 were seen at all visits and 36 were excluded owing to noncompliance. Of 478 infants who completed the study, 232 were exclusively breast-fed, 79 received an extensively hydrolyzed casein formula (Nutramigen), 82 an extensively hydrolyzed whey formula (Profylac), and 85 a partially hydrolyzed whey formula (Nan HA), during the first 4 months of life. These four groups were identical in regard to atopic predisposition, cord blood IgE, birthplace, and gender. Exclusively breast-fed children were exposed less to tobacco smoke and pets at home and belonged to higher social classes, whereas the three formula groups were identical concerning environmental factors. The frequency of breast-feeding was high; only eight (2%) children were not breast-fed at all. The three formula groups were identical in regard to duration of breast-feeding and age at introduction of formula and solid foods. No significant differences were found in the three groups of infants receiving formula milk regarding the cumulative incidence of atopic dermatitis or respiratory symptoms. The cumulative incidence of parental-reported cow's milk allergy was significantly higher in children fed partially hydrolyzed formula (Nan HA) compared with extensively hydrolyzed formula (Nutramigen or Profylac) at 12 and 18 months (NanHA, 7.1%; Nutramigen, 2.5%; Profylac, 0%; p=0.033). The cumulative incidence of confirmed cow's milk allergy was 1.3% (three of 232) in exclusively breast-fed infants, 0.6% (one of 161) in infants fed extensively hydrolyzed formula (Nutramigen or Profylac), and 4.7%(four of 85) in infants fed partially hydrolyzed formula (Nan HA). Partially hydrolyzed formula was found to be less effective than extensively hydrolyzed formula in preventing cow's milk allergy, 0.6% vs. 4.7% (p=0.05), but because of the small number of cases the results should be interpreted with caution. Compared with other similar studies the frequency ofatopic symptoms was low, even though the dietetic intervention did not include either maternal diet during lactation or dietary restrictions to the children after the age of 4 months.

The natural history of cow's milk protein allergy/intolerance.

In prospective studies th incidence of cow's milk protein allergy and intolerance (CMPA/CMPI) in infancy in western industrialized countries has been estimated to be about 2-3% based on strict diagnostic criteria. A significant association between early neonatal exposure to cow's milk formula feeding and subsequent development of CMPA/CMPI has been documented. The small amounts of 'foreign' protein in human milk may rather induce tolerance than allergic sensitization. The findings of specific IgE to individual cow's milk proteins in cord blood of the majority of infants who later develop CMPA/CMPI suggests a prenatal sensitization may play a role in the pathogenesis of CMPA/CMPI. Perhaps a weak intrauterine education of low IgE-response may need to 'boosted' neonatally in order to cause clinical disease. The prognosis of CMPA/CMPI is good with a recovery of about 45-56% at one year, 60-77% at two years and 71-87% at three years. Associated adverse reactions to other foods, especially egg, soy, peanut and citrus develop in about 41-54%. Allergy to potential environmental inhalant allergens has been reported in up to 28% by three years and up to 80% before the age of puberty. Especially, infants with an early increased IgE response to cow's milk protein have an increased risk of persisting CMPA, development of persistent adverse reactions to other foods and development of allergy against environmental inhalant allergens. Cow's milk protein/intolerance (CMPA/CMPI), meaning reproducible adverse reactions to cow's milk protein(s) may be due to the interaction between one or more milk proteins and one or more immune mechanisms, possible any of the four basic types of hypersensitivity reactions. Immunologically mediated reactions are defined as CMPA. Mostly, CMPA is caused by IgE-mediated (type I) reactions, but evidence for type III (immune complex) reactions and type IV (cell mediated reactions) have been demonstrated as reviewed by Høst (1994) and Ortolani & Vighi (1995). Non immunologically reactions against cow's milk protein(s) are defined as CMPI. However, it should be stressed that many studies on 'cow's milk allergy' have not investigated the immunological basis of the clinical reactions. In most instances of cow's milk protein hypersensitivity only diagnostic investigations such as skin prick test and RAST indicative of IgE-mediated reactions are performed. In fact, CMPA cannot be ruled out unless extensive diagnostic tests for type II-III-IV reactions have proved negative. Thus, the classification of adverse reactions to cow's milk proteins depends on the extent and the quality of performed diagnostic tests for immune mediated reactions. At present, no single laboratory test is diagnostic of CMPA/CMPI, and differentiation between CMPA and CMPI cannot be based solely on clinical symptoms. Therefore the diagnosis has to be based on strict well-defined elimination and milk challenge procedure (Hill & Hosking, 1991), (Høst, 1994). Preferably, double-blind placebo-controlled challenges (DBPCFC) should be carried out in children older than 1-2 years of age. In infants open controlled challenges have been shown to be reliable when performed under professional observation in a hospital setting (Høst & Halken, 1990).

The effect of hypo-allergenic formulas in infants at risk of allergic disease.

Development of atopic disease seems to depend on both genetic factors and exposure to several environmental factors. At present ther is evidence that the mode of early infant feeding influences the development of food allergy, whereas daily exposure to inhalant allergens and daily exposure to tobacco smoke is found to be associated with an increased risk of recurrent wheezing/asthma and inhalant allergy. In infants with atopic predisposition (first-degree relatives), exclusively breastfeeding > or = four months is found associated with a significant reduction of the cumulative prevalence of cow's milk allergy/intolerance (CMA/CMI) during the first 1-2 years of age. When breastmilk is insufficient or lacking a substitute formula is needed. Several recent prospective studies show a preventative effect of extensively hydrolysed formula (eHF) in combination with avoidance of cow's milk proteins and solid foods during > or = 4 months in high-risk infants on the cumulative prevalence of food allergy and atopic dermatitis during the first 2-4 years of life. Partially hydrolysed formulas (pHF) may be effective in allergy prevention, but due to drawbacks of study design and lack of documentation pHF cannot be recommended at present. The results of studies comparing the preventive effect of eHF and pHF are awaited. The protective effect on the development of cow's milk allergy is a real prevention and not only a postponement of the onset of symptoms. No studies have demonstrated a preventive effect of dietary measures as regards asthma/inhalant allergy, at present until the age of four years. As no studies concerning the preventive effect of avoidance of milk and other foods after the age of 4-6 months of life have been performed, recommendation of preventive elimination diets beyond this age is empirically based. In order to reduce the costs, to minimize the risk of stigmatisation and the risk of malnutrition it is important to avoid unnecessary restrictive and prolonged diets. A diet period of 4-6 months seems sufficient in most infants. At present eHF are recommended for avoidance of cow's milk. Some high risk infants may benefit from maternal diet during lactation, but there is no documented beneficial effect of maternal diet during pregnancy.