Management of Neonatal Isolated and Combined Growth Hormone Deficiency: Current Status

Congenital growth hormone deficiency (GHD) is a rare disease caused by disorders affecting the morphogenesis and function of the pituitary gland. It is sometimes found in isolation but is more frequently associated with multiple pituitary hormone deficiency. In some cases, GHD may have a genetic basis. The many clinical signs and symptoms include hypoglycaemia, neonatal cholestasis and micropenis. Diagnosis should be made by laboratory analyses of the growth hormone and other pituitary hormones, rather than by cranial imaging with magnetic resonance imaging. When diagnosis is confirmed, hormone replacement should be initiated. Early GH replacement therapy leads to more positive outcomes, including reduced hypoglycaemia, growth recovery, metabolic asset, and neurodevelopmental improvements.


Introduction
Severe congenital growth hormone (GH) deficiency (GHD) in newborns is a rare disease with a reported incidence of between 1:4000-1:10,000 and 1:20,000 newborns [1,2]. Congenital GHD is commonly secondary to anomalies in the morphogenesis and function of the pituitary gland and is often associated with multiple pituitary hormone deficiency (MPHD); nevertheless, GHD can also be isolated (IGHD) [1][2][3][4][5]. IGHD or MPHD may also occur as a result of a genetic syndrome causing abnormalities in extra-pituitary structures that have a common embryological origin to the pituitary gland [4][5][6][7]. Acquired forms of GHD or MPHD may occur because of perinatal or neonatal events [6].
Understanding the different phenotypes, morphological findings and abnormalities is fundamental for establishing the disease's etiology and for effective follow up [15,16]. The genetic etiologies of GHD/MPHD are summarized in Table 1. Table 1. Etiology and risk factors of neonatal IGHD/MPHD.

Congenital infections Breech delivery/asphyxia
Midline defect syndromes (e.g., septo-optic dysplasia) Neonatal sepsis Gene mutations * * a detailed list of mutations and characteristics of genes involved in pituitary gland development are reported in Table 2. GHD: growth hormone deficiency. MPHD: multiple pituitary hormone deficiency.
The aim of this review is to describe the etiology, clinical signs and symptoms, and diagnosis of isolated GHD and MPHD. We highlight the importance of introducing effective therapy during the neonatal period.

Clinical Presentation
GHD can be isolated (IGHD) or associated with other hormone deficiencies (MPHD). Pituitary deficiencies can involve all the pituitary hormones, including the antidiuretic hormone (ADH) responsible for central or neurogenic diabetes insipidus (DI) [4,7].
Patients have varied and heterogeneous symptoms, according to the severity and number of hormones affected ( Table 3). The most common symptoms in newborns are hypoglycaemia, midline abnormalities, micropenis, and prolonged jaundice with cholestasis. Neurological symptoms and psychomotor delay are possible and range from focal deficits to global developmental delay, depending on the underlying genetical anomaly [17]. Table 3. Symptoms and signs suggestive for IGHD/MPHD.

Symptoms and Signs IGHD MPHD (Hormone Deficit)
Hypoglycaemia (with and without seizures) During the neonatal period, the most frequent presenting feature of congenital GHD is severe hypoglycaemia [18] persisting beyond three days, often in the absence of hyperinsulinism, which may be associated with seizures leading to potential brain damage [1][2][3][4][5][6][7][8][9][10]. This suggests that during the perinatal period, together with cortisol, GH is essential for the regulation of glucose homeostasis [6]. The incidence of hypoglycaemia does not appear to correlate with birth size or severity of GHD, but with the presence of an additional hormone deficiency, particularly with concomitant adrenocorticotropic hormone (ACTH) deficiency [3].
Another typical clinical feature of GHD is the presence at birth, in affected boys, of a micropenis [19][20][21], defined according to a −2.5 standard deviation (SD) cut-off from the mean value. This may result from IGHD or, more frequently, from combined GH and gonadotropin deficiencies [6]. The micropenis may improve when treatment with GH is initiated, suggesting that GH may be critical in penile growth in foetal and early postnatal life [4,6,7]. Some children with GHD or MPHD present with neonatal cholestasis with normal liver parameters and normal gamma-glutamyl transferase levels [22][23][24][25][26][27], as first described in 1956 [28]; for the review: see [29]. The exact cause of this form of hepatitis is not well understood, although GH has been shown to modulate bile acid synthesis and bile acid secretion [22][23][24][25][26]. Central hypothyroidism and hypocortisolism have also been shown to cause conjugated hyperbilirubinemia [29]. There could be several predisposing factors, such as the immaturity of the hepatic excretory function, a susceptibility to viruses or toxins, and a stereotypic response of the immature hepatocyte to injury [22,29]. Prolonged neonatal jaundice may indicate central hypothyroidism [30] and cortisol deficiency can also cause neonatal cholestatic hepatitis [31]. Cholestasis usually resolves spontaneously during the first few months of life. Hormone replacement with GH, L-thyroxine (L-T 4 ), and hydrocortisone, in addition to routine intervention for cholestasis, for example with ursodeoxycholic acid, seems to accelerate recovery [22,24,26].
Intrauterine growth is believed to be independent of GH action since most affected newborns present with normal birth length. Some studies have reported early postnatal growth failure, suggesting that GH may be a significant influence on linear growth in this period [3,10,[32][33][34][35][36][37].
A careful and detailed medical history is mandatory to obtain information about a possible etiology. Information should be gathered on potential predisposing factors, including parental consanguinity, index cases, traumatic/breech birth, neonatal central nervous system infection, and prenatal or birth asphyxia [38]. In a paper evaluating children with hypopituitarism, 7.7% of patients with isolated GHD had a history suggestive of birth asphyxia [39]. Physical examination is also fundamental; for example, height, weight and head circumference should be measured in newborns. Fontanelle size, eyes, microphallus and undescended testicles in males, cleft palate/lip, hepato-splenomegaly, lymphadenopathy, jaundice, and malformations need to be assessed [39][40][41]. Although the diagnosis of MPHD is typically established during the neonatal period, the initial manifestation may occur later in the form of psychomotor delay. In the absence of signs in the neonatal period, early diagnosis may be missed, which can lead to neurocognitive impairment and neurological sequelae [40]. The thyroid hormone (TH) is critical for normal brain development within the first 3 years of life, and a prompt diagnosis of hypothyroidism means that treatment can be commenced immediately to avoid neurocognitive damage. The data suggest that it is just as important to make an early diagnosis of GHD, so that prompt treatment can be introduced to ensure normal brain development [42].
Conventional GH stimulation tests are not recommended because they can be dangerous under 12 months of age. Measuring random basal GH serum concentrations [4][5][6][7] can confirm diagnosis. In the first week of life, infants have relative hypersomatotropism, with random GH levels higher than older children and adults [5,7,43].
GH can be measured in serum or plasma during the first week of life, and thereafter in the stored newborn screening card [5]. Because of GH assay variability, a random GH value of ≤5 µg/L in the first week of life in a neonate with deficiency of other pituitary hormones and hypoglycaemia or pituitary radiological abnormalities is sufficient to distinguish infants with GHD [32,43,44]. Nevertheless, Binder et al. have suggested an ideal GH cut-off of 7 µg/L during the first week after birth [5].
In children, insulin-like growth factor-1 (IGF-1), and insulin-like binding protein-3 (IGFBP-3) are commonly used markers of GH secretion. In the neonatal period, Jensen et al. [45] reported that low serum levels of these markers, below 2SD for days of life, have a high sensitivity (90% for IGF-1 and 81% for IGFBP-3), suggesting that both IGF-1 and IGFBP-3 can be utilized as auxiliary diagnostic tools for GHD [32,43,44].
In the hypothalamus-pituitary-thyroid axis, central congenital hypothyroidism (CH) may be defined as inadequate TH production caused by quantitative or qualitative thyroidstimulating hormone (TSH) deficiency, leading to TH deficiency in target tissues [46,47]. Biochemically, the patients show FT 4 concentrations below the reference range associated with normal, low, or slightly elevated TSH levels [47]. The assumption that central CH may be a mild condition has been refuted, and it is critical that neonates are diagnosed shortly after birth. Unfortunately, the data show that most neonates with central CH are diagnosed late, even though many are hospitalized in the first weeks of life for feeding problems, hypoglycemia, or (prolonged) jaundice [46,47]. At present, only a few newborn screening (NBS) programs detect central CH [47]. It is important to remember that, while making a diagnosis of primary hypothyroidism based on elevated TSH is relatively simple, diagnosing central CH is less straightforward, as it calls for the correct interpretation of FT 4 concentrations. If serum FT 4 is clearly below the reference range, signs or symptoms of hypothyroidism are present and/or the patient's medical history is suggestive of hypothalamic or pituitary damage or disease, diagnosis is easier [47], but in some patients, clear signs or symptoms are absent and the medical history is uninformative [47].
The circadian rhythm is established at two [48] to after six months of age [49]; thus, morning cortisol concentrations are not useful in evaluating ACTH deficiency in newborns [6]. Furthermore, low cortisol concentrations, even during a hypoglycaemia episode, have too low a specificity for a diagnosis of adrenal insufficiency [50], and therefore a dynamic assessment (both a low-dose and standard ACTH stimulation testing using tetracosactide hexaacetate) is mandatory [6]. The correct dose of tetracosactide hexaacetate, the optimal timing of blood samples of cortisol measurements, and the cut-off of the peak cortisol concentration, have not been unequivocally established, but stimulated cortisol concentrations ≥18 mg/dL (497 nmol/L) may be considered as indicative of a normal hypothalamo-pituitary-adrenal axis [51].
Gonadotropic hormone deficiencies are confirmed by low levels of plasma gonadotropins, and, in male infants, of testosterone and inhibin B [4,6,7].
Magnetic resonance imaging (MRI) of the pituitary gland can help identify congenital and structural disorders [52][53][54][55]. With sagittal T1-weighted sequences, the posterior pituitary appears as a hyperintense bright spot, while the anterior pituitary is similar in signal intensity to grey matter [53,54]. The gland is proportionally larger in the neonatal period than in childhood. Normal values for the pituitary gland in newborns are elsewhere summarized [7]. A calibre of the stalk of less than 1 mm at any point is generally considered thin [7,53].
Children diagnosed with GHD during the newborn period have a high incidence of neuroanatomical anomalies of the hypothalamic-pituitary region, with a wide spectrum of variations in pituitary anatomy [52][53][54][55]. The most common radiological findings are ectopic posterior pituitary, hypoplastic or aplastic anterior pituitary and an absent or thin pituitary stalk, and an empty sella, even if patients with a normal MRI have also been reported [52][53][54][55].
In infants with isolated GHD, a normal or hypoplastic pituitary gland, empty sella without anatomical abnormalities of the hypothalamus or pituitary stalk are the most frequent imaging features, while a moderate-to-severe hypoplastic pituitary gland (pituitary height ≤ 3 mm) with ectopic posterior pituitary is more frequent in infants with MPHD [55].
Finally, molecular studies may be fundamental for correctly evaluating patients [6]. Genetic studies should consider patient history and clinical data, as well as laboratory and radiological findings [7,16].

Treatment and Follow-Up
A multidisciplinary team, including paediatricians, paediatric endocrinologists, geneticists, radiologists, ophthalmologists, and neurologists, should follow and treat infants with GHD [6]. Careful follow-up is mandatory, considering that additional hormone deficiencies may develop, and suitable hormonal treatments could be necessary [4,6,7].
When MPHD is diagnosed, it is important to measure cortisol levels so that newborns with cortisol deficiency can start oral hydrocortisone [4,6,7]. In the case of stress or significant illness, the dose should be doubled or tripled [4].
Oral L-T 4 is the specific treatment for central hypothyroidism, starting with 50 µg/m 2 per day or 6-8 to 10/15 microgram/kg/day with the aim of keeping free thyroxine levels in the upper normal range [4,6,56,57]. After starting treatment, the dose needs to be monitored by measuring free thyroid hormone concentrations. TSH levels should not be monitored as the patients are TSH-deficient [4,6,56]. Higher L-T 4 doses will be needed in newborns with cholestasis due to malabsorption [57,58]. Attention must be given to patients taking iron, soy, calcium, and anticonvulsants [57,58], that can affect L-T 4 absorption and thus should not be co-administered [58]. Before starting treatment with L-T 4 , it is extremely important to exclude cortisol deficiency, because L-T 4 increases the basal metabolic rate, enhancing cortisol clearance with the subsequent risk of precipitating an adrenal crisis [4,6,7].
In cholestatic infants, treatment with L-T 4 and hydrocortisone could require higher doses due to absorption deficiency; the dose should be reduced when cholestasis improves [59].
In newborns diagnosed with GHD, whether IGHD or MPHD, recombinant human GH (r-hGH) replacement should be started. Since diagnosis is often delayed and treatment started after the neonatal period [62], the data in the literature are very limited. Here, we focus on the outcomes of early GH replacement treatment and attempt to determine the best timing and dosage of replacement therapy.
When GHD is the recognized cause of persistent hypoglycaemia, replacement therapy with r-hGH, contributes to hypoglycaemic recovery [63][64][65]. Costa et al. describe a child with CHARGE syndrome in whom GHD was diagnosed in the second month of life due to hypoglycaemic episodes: r-hGH was initiated at day 86 (30 µg/kg/day) suggesting that treatment with GH may restore normal glucose homeostasis rather than maintain normal linear growth [66]. Even in other syndromic conditions, the euglycaemic state can be restored by r-hGH replacement. Bonfig et al. [67] describe a 1.5-month-old girl with Turner syndrome and recurrent hypoglycaemia related to GHD: r-hGH therapy was started at a dose of 25-30 µg/kg/day and subsequently doubled (50 µg/kg/day), until blood glucose was normalized.
Early diagnosis and the fast replacement of r-hGH, in addition to increased energy intake and other counterregulatory hormones, seems to prevent recurrent and prolonged hypoglycaemia, although hypoglycaemia may occasionally present in older children during stressful periods associated with reduced oral intake [4].
When GHD is recognized during the first years of life and r-hGH substitutive treatment is started early, short-term and long-term studies demonstrate a marked catch-up growth and significant height gain [34,42,68,69].
GH replacement does not only have a promoting effect on children's growth but also important metabolic effects [41]. Even at a young age, GHD may show subtle metabolic changes that can adversely affect their future metabolic and atherogenic profile [42]. On the contrary, early treatment could have metabolic effects similar to those reported in patients with Prader-Willi syndrome; in these patients, early r-hGH treatment, before the age of 2 years, is associated with improvements in body composition, motor function, height, and lipid profiles, compared to those who are untreated [70,71]. Further studies are required to clarify the effect of replacement therapy on metabolic asset in GHD infants.
Considering that GH plays an important role in early brain development, maturation, and function, it can be hypothesized that delaying GH treatment could alter brain growth and cognitive abilities [42,[72][73][74]. Children diagnosed with congenital pituitary hormone deficiencies may have lower-than-average cognitive functions, and specific difficulties with perceptual organisation compared to siblings [67]. This could be due to various factors such as hypoglycaemia in early life, thyroxine deficiency, or abnormal central nervous system development [72].
Previous studies have reported that treatment with r-hGH, given at dosage of 0.3 µg/kg/day, in association with psychomotor and cognitive stimulation, clearly improves neurodevelopment in children with cerebral palsy [75,76].
The "plastic" function of GH on neuronal structuring and development should be carefully evaluated when considering whether to start r-hGH treatment early, especially when there is a certain diagnosis of GHD but there are no symptoms of classical hormonal deficiency [42]. Although data on GH dosage are scant, a dosage of 25-50 µg/kg/day has been suggested during the first year of life [36,[68][69][70].
Considering the lack of data for the neonatal period, careful monitoring is recommended. A low frequency of side effects in older children (intracranial hypertension, slipped capital femoral epiphysis, scoliosis progression) has been reported when r-hGH is used at a conventional dosage [36].
When ACTH deficiency is suspected, hydrocortisone treatment should be started immediately [4,6,7]. Hydrocortisone is the treatment of choice due to its less potent side effects in terms of growth and bone health compared to other glucocorticoids [4,6,7]. The starting dose is 9-12 mg/m2/day, divided into 3-4 doses; a dose higher than for older infants because neonates have greater cortisol secretion rates [4,6,7]. Prior to hospital discharge, families must be instructed about emergency dosing and dosing during illness or periods of stress when a doubling or even tripling of the normal dose is required [4,6,7]. In cases of emergencies, poor tolerance of oral hydrocortisone, or a suspected adrenal crisis, intramuscular hydrocortisone must be administered (<1 year 25 mg, 1-5 years 25-50 mg, >5 years 100 mg) and oral glucose should also be given to correct any associated hypoglycaemia [4,6,7]. Patients who cannot tolerate oral hydrocortisone require hospital admission for intravenous hydrocortisone (1-2 mg/kg every 4-6 h) [4,6,7]. In patients able to tolerate oral hydrocortisone, a triple or double maintenance dose is recommended that can be tapered to a lower dose after clinical improvement [4,6,7].
It is also important to highlight that cortisol deficiency can mask DI, as cortisol is needed for water excretion. DI may develop after starting treatment with hydrocortisone, and therefore close monitoring of fluid balance and electrolytes is important after starting glucocorticoid therapy [51].
Novel treatments, such as continuous subcutaneous hydrocortisone infusion therapy, which may be difficult in neonates due to limited subcutaneous fat for insertion of the cannula, and sustained release hydrocortisone preparations aimed at mimicking physiological cortisol secretion, may become therapeutic options in the future [77].
In newborn male infants, the aim of androgen treatment is to ensure normal testicular descent, improve penile length, and maximize fertility in later life. This treatment will have to be resumed at the time of puberty. In newborns, early treatment is recommended, ideally between 1 and 6 months of age. Testosterone can be given via intramuscular injections or topical gel [60,[78][79][80]. Testosterone injections (cypionate or enanthate) are commenced at a recommended dose of 25 mg every 4 weeks for 3 months. This is followed by clinical evaluation of the stretched penile length. Topical gel containing 5-α Dihydrotestosterone (DHT) is also useful, and the recommended starting dose is 1 application (10 mg) every day for 3 months [78]. The carer who is applying the testosterone gel should wash their hands immediately after administration with soap and water and, if the carer is a female, the use of gloves is recommended. Cryptorchidism increases the risk of testicular neoplasia and reduces fertility potential, therefore surgical correction (orchidopexy) is recommended during the first 2 years of life, ideally by 18 months of age [81]. Treatment with LH and FSH during the neonatal period is under investigation [82][83][84].

Conclusions
Congenital GHD comprises a spectrum of diseases that may cause an isolated deficiency of GH or may be part of a syndrome of MPHD. Clinical manifestations are variable, and include hypoglycemia, micropenis, and cholestasis, in addition to growth problems that often appear later. Therapeutic management should evaluate the clinical signs and the associated hormone deficiencies.
The aim of our work is to summarize the etiology, clinical presentation, diagnosis and current state of therapy for GHD during the neonatal period. Given the wide spectrum of phenotypes and considering that many of the presenting symptoms are non-specific, identifying infants with congenital hypopituitarism is not always simple.
Nevertheless, early identification of GHD is important, because undiagnosed pituitary hormone deficits can lead to significant morbidity and possible mortality.
Most studies have demonstrated the positive role of r-hGH replacement therapy in children affected by GHD, but data on outcomes, timing, and dosage are scant. We strongly recommend the early introduction of GH treatment in GHD, before growth retardation becomes evident. There are clear metabolic and auxological benefits of early intervention. Early diagnosis and the fast replacement of r-hGH seem to prevent recurrent and prolonged hypoglycaemia. In combination with cortisol, this treatment promotes significant catch-up growth.
We also underline that GH could have a plastic role on neuronal structuring during the first years of life, and that untreated GHD could be damaging to brain structure and psychological and neurological development. Further research into therapies for GHD in the neonatal period should be encouraged.