Isolated hypoprolactinemia: The rarest of the rare?

Isolated hypoprolactinemia (IHP) can be defined as the presence of consistently low serum levels of prolactin in the absence of other anterior pituitary hormone abnormalities. It is an extremely rare condition, and consequently incompletely understood and unrecognized. A recent study has reported the first cases of IHP caused by mutation in the PRL gene. There are also cases where the pathogenesis of IHP is likely secondary to an autoimmune response against the PRL-secreting cells. But most published cases are acquired and idiopathic. The best characterized function of PRL is to facilitate milk production in the puerperium. Analysis of the GTEX data repository, however, shows that PRL is the most abundantly expressed gene in the human pituitary, independently of gender and age, suggesting the presence of additional roles for PRL. Newer studies have indeed revealed a much larger spectrum of PRL functions and will likely uncover novel clinical phenotypes associated with severe PRL deficiency.

Evidence-based definition of hypoprolactinemia in European men aged 40-86 years: the European male ageing study

Empirical evidence for a low normal or reference interval for serum prolactin (PRL) is lacking for men, while the implications of very low PRL levels for human health have never been studied. A clinical state of "PRL deficiency" has not been defined except in relation to lactation. Using data from the European Male Ageing Study (EMAS), we analyzed the distribution of PRL in 3,369 community-dwelling European men, aged 40-80 years at phase-1 and free from acute illnesses. In total, 2,948 and 2,644 PRL samples were collected during phase-1 and phase-2 (3 to 5.7 years later). All samples were analysed in the same centre with the same assay. After excluding individuals with known pituitary diseases, PRL ≥ 35 ng/ml, and PRL-altering drugs including antipsychotic agents, selective serotonin reuptake inhibitors, or dopamine agonists, 5,086 data points (2,845 in phase-1 and 2,241 in phase-2) were available for analysis. The results showed that PRL declined minimally with age (slope = -0.02) and did not correlate with BMI. The positively skewed PRL distribution was log-transformed to a symmetrical distribution (skewness reduced from 13.3 to 0.015). Using two-sigma empirical rule (2[]SD about the mean), a threshold at 2.5% of the lower end of the distribution was shown to correspond to a PRL value of 2.98ng/ml. With reference to individuals with PRL levels of 5-34.9 ng/ml (event rate = 6.3%), the adjusted risk of developing type 2 diabetes increased progressively in those with PRL levels of 3-4.9 ng/ml: event rate = 9.3%, OR (95% CI) 1.59 (0.93-2.71), and more so with PRL levels of 0.3-2.9 ng/ml: event rate = 22.7%, OR 5.45 (1.78-16.62). There was also an increasing trend in prediabetes and diabetes based on fasting blood glucose levels was observed with lower categories of PRL. However, PRL levels were not associated with cancer, cardiovascular diseases, depressive symptoms or mortality. Our findings suggest that a PRL level below 3 ng/ml (64 mlU/l) significantly identifies European men with a clinically-important outcome (of type 2 diabetes), offering a lower reference-value for research and clinical practice.

Correlations Among Maternal and Infant Factors, Lead Exposure, and Serum Prolactin Levels During Lactation: A Cross-sectional Study in Indonesia

OBJECTIVES

Prolactin is vital for breastfeeding and milk production, and its secretion is influenced by factors related to the mother, infant, and environment. To date, no study has concurrently investigated the correlation of these factors with serum prolactin levels during lactation. Therefore, the objective of this study was to investigate the correlations among maternal and infant factors, lead exposure, and serum prolactin levels during lactation.

METHODS

A cross-sectional approach was employed in Surabaya, Indonesia, among 110 exclusively lactating mothers. The mothers' daily diets were determined using multiple 24-hour recalls, while blood lead levels were measured with inductively coupled plasma mass spectrometry. Serum prolactin levels were assessed using the electrochemiluminescence immunoassay. For bivariate analysis, we employed the Spearman correlation, Mann-Whitney, and Kruskal-Wallis tests, while for multivariate analysis, we utilized multiple linear regression.

RESULTS

The average serum prolactin level of the lactating mothers was 129.19±88.96 ng/mL. Positive correlations were found between serum prolactin levels and breastfeeding frequency (p < 0.001), protein intake (p < 0.001), and calcium intake (p = 0.011) but had negative correlation with blood lead levels (p < 0.001) and vitamin B6 intake (p = 0.003). Additionally, prolactin levels were not significantly associated with maternal age; parity; intake of calories, vitamin D, vitamin E, zinc, folic acid, magnesium, or iron; infant age; or infant sex.

CONCLUSIONS

Breastfeeding frequency had a stronger positive relationship with serum prolactin levels than protein and calcium intake. However, lead exposure was associated with reduced serum prolactin levels during lactation. Consequently, specific interventions from policymakers are necessary to manage breastfeeding in mothers exposed to lead.

Genetic and Physiological Factors Affecting Human Milk Production and Composition

Human milk is considered the optimal nutrition for infants as it provides additional attributes other than nutritional support for the infant and contributes to the mother's health as well. Although breastfeeding is the most natural modality to feed infants, nowadays, many mothers complain about breastfeeding difficulties. In addition to environmental factors that may influence lactation outcomes including maternal nutrition status, partner's support, stress, and latching ability of the infant, intrinsic factors such as maternal genetics may also affect the quantitative production and qualitative content of human milk. These genetic factors, which may largely affect the infant's growth and development, as well as the mother's breastfeeding experience, are the subject of the present review. We specifically describe genetic variations that were shown to affect quantitative human milk supply and/or its qualitative content. We further discuss possible implications and methods for diagnosis as well as treatment modalities. Although cases of nutrient-deficient human milk are considered rare, in some ethnic groups, genetic variations that affect human milk content are more abundant, and they should receive greater attention for diagnosis and treatment when necessary. From a future perspective, early genetic diagnosis should be directed to target and treat breastfeeding difficulties in real time.