Severe obesity with hypo-leptinemia

Abstract

Some cases of obesity are thought to be associated with hypo-leptinemia. This may cause decreased appetite suppression resulting in increased appetite, leading to weight gain. Replacement therapy with leptin might be theoretically useful, but verification by reporting more cases is required. Here, we first investigated the serum leptin levels and their correlation with body mass index (BMI) in 107 patients with obesity to identify the subjects with hypo-leptinemia. Among them, one patient with congenital hypopituitarism was further investigated by comparison of his clinical and pathological characteristics with those of control subjects. This 40-year-old Japanese man, who was large from birth, consistently showed obesity of more than 2SD during his growth period. He had 41.5 kg/m² at BMI with central hypogonadism, central diabetes insipidus and severe growth hormone deficiency, cognitive impairment, and abnormal eating behavior, which led to suspicion of the involvement of hypothalamic factors. Genetic analysis revealed no definite mutations regarding metabolic and nutritional systems or adipocytes including leptin-related genes. Electron microscopic images of subcutaneous adipose tissue demonstrated relatively smaller adipocytes compared with a BMI-matched patient. The patient suffered from his abnormal eating behavior, began dialysis at the age of 41 years, and died of bacterial pneumonia at 49 years of age. Among patients with severe obesity with hypo-leptinemia, there could be patients with disturbance of healthy expansion in adipocyte, probably due to unknown dysfunction. Even with the lack of abnormality of leptin-related genes, indication of leptin-replacement may be considered for severely obese patients with hypo-leptinemia.

Background

Obesity and obesity-related diseases, including diabetes and hypertension, are important issues of health policy in many countries, including Japan [1]. Most cases of obesity are considered to be primary obesity, which has no single definite cause, while the remainder are secondary obesities, such as endocrine-related, drug-related, and hypothalamic obesity [2]. Detailed assessments including endocrinological, genetic and environmental factors could be a key to selecting the appropriate therapy in cases of severe obesity.

Leptin is secreted by adipocytes and acts on its receptors in the hypothalamus to induce weight loss by suppressing eating and increasing energy expenditure [3]. Leptin levels generally show a good positive correlation with body mass index (BMI) and body fat percentage, and they are markedly elevated in obese individuals [4]. When severe obesity is accompanied by congenital central pituitary dysfunction and/or involvement of the hypothalamus, leptin gene-related abnormalities are suspected. Among them, dysregulation of leptin and its receptor gene have similar clinical phenotypes known to coexist with hyperinsulinemia, hypothalamic hypothyroidism, and hypogonadotropic hypogonadism [5]. Hypo-leptinemia is generally seen in lipodystrophy, showing a severe decrease in body fat mass, and cases of lipoatrophy are indicated for leptin replacement therapy [6]. On the other hand, clinical trials of leptin in simple obese subjects have not demonstrated sufficient effects on weight loss in the physiological concentration range due to their leptin resistance [7]. Meanwhile, in patients with obesity caused by leptin gene mutations, leptin replacement therapy at physiological doses has been proven to safely and effectively reduce food intake and body weight [5]. Conditions associated with hypo-leptinemia may therefore exist in some severely obese patients, who may benefit from leptin replacement therapy. In this context, we suggest that further accumulation of cases of obesity in relation to hypo-leptinemia has been warranted.

Here, we first investigated the serum leptin levels and their correlation with BMI in the patients with obesity to identify the subjects with relative hypo-leptinemia. Among them, we further investigated a unique case of a severely obese patient who had relative hypo-leptinemia, hypopituitarism, and involvement of the hypothalamus by comparing his clinical and pathological characteristics with those of control subjects. It may be useful to consider the indication of leptin replacement therapy for severely obese patients with hypo-leptinemia.

Materials and Methods

Measurements of serum leptin levels

Serum samples were casually collected on routine visits to the outpatient clinic. Serum leptin levels were measured by either RIA kit (Human Leptin RIA, LINKO Research Inc. St Charles, MO, USA) or ELISA kit (Human Leptin ELISA, Cosmic Corporation, Tokyo, Japan) as indicated in the text, in accordance with the manufacturer’s instructions. The serum leptin levels described in the result section and Fig. 1 were measured by ELISA kit. Additionally, relatively low serum leptin concentrations were confirmed by RIA assay as well. All the samples for the measurements of serum leptin concentrations were collected after the overnight fasting, with the typical fasting period being 12 h. Correlation between serum leptin levels and BMI was analyzed by statistical testing of Pearson’s correlation coefficient.

Fig. 1  Serum leptin concentration in the current patient and control subjects (N = 107, BMI: 33.9 ± 0.5 [mean ± SE] kg/m²). Pearson’s correlation coefficient (r): 0.6725, p-value: <0.001. Focused patient in text is indicated by red diamond.

Genetic analysis

Human genome analysis was performed as previously reported [8]. Briefly, all human coding exons were captured from the genomic deoxyribonucleic acid of the proband with specific probes (TruSeq Nano DNA Sample Prep Kit; Illumina, CA, USA), and the products were sequenced with a next-generation sequencer (cBOT and HiSeq X; Illumina, CA, USA). The generated reads were annotated with reference sequences in accordance with the algorithm of Riken Genesis (Kanagawa, Japan).

Scanning electron microscopy (SEM)

Abdominal subcutaneous adipose tissue samples were collected during surgery from both the current patient and a control subject. The subcutaneous adipose tissues were immediately cut out, fixed in 2.5% glutaraldehyde in 0.1 M phosphate buffer pH 7.4 for 2 h, and post-fixed in 1% osmium tetroxide in 0.1 M phosphate buffer for 1 h. Then, they were dehydrated through graded concentrations of ethanol (50–100%), and freeze-dried in t-butyl alcohol. The preparations were mounted on specimen-holders for SEM with silver paste, coated with gold, then observed in SEM (S-3000N, HITACHI, Tokyo, Japan).

Results

Measurements of serum leptin levels with recovery experiments

To identify subjects with relative hypo-leptinemia, we first examined serum leptin levels and their correlation with BMI in 107 Japanese patients with obesity (BMI: 33.9 ± 0.5 kg/m², r: 0.6725, p-value: <0.0001) (Fig. 1). Among them, we identified a unique case of a patient with severe obesity (details below), whose serum leptin concentrations were 5.8, 8.4, and 11.1 ng/mL, measured at three independent time points. These values were relatively low compared with other obese male controls with equivalent BMI. A representative assay result, with this patient’s case indicated as a red diamond, is shown in Fig. 1.

To rule out an abnormal measurement system as the cause of the low leptin concentration, we performed a recovery experiment to determine if there were any factors that interfered with the leptin measurement. The leptin concentrations of 5.0 ng/mL, 20.0 ng/mL, and 100.0 ng/mL were added to the patient’s serum, and we measured their concentrations. The results were similar to the predicted leptin concentrations (Fig. 2), suggesting that in this case the presence of inhibitory factors affecting the measurement of leptin concentration was limited.

Fig. 2  A recovery experiment to rule out an abnormal measurement system. Measured leptin concentrations were similar to the predicted ones in each indicated concentration.

Thus, we further focused on this patient by comparing his clinical and pathological characteristics with those of control subjects.

Clinical characteristics with assessments of eating behavior questionnaire

A 40-year-old Japanese man with severe obesity was admitted for examinations for obesity and other endocrinological impairments. His birth weight was 4,300 g. He was born 17 days post term. He was consistently considered to be obese, weighing 76.6 kg at 15 years old, exceeding 100 kg at 16 years old, and 120 kg at 20 years old. His maximum weight was 145 kg at the age of 38 years, with a BMI of 51.4 kg/m². His height was approximately average at the age of 7 years, then gradually deviating from the growth standards for Japanese children with percentile values based on the year 2000 national survey data [9] and falling below –1 SD from the age of 14, but never falling below –2 SD (Fig. 3).

Fig. 3  Growth Curve. The growth standards for Japanese children with percentile values were based on the year 2000 national survey data (Isojima T et al., Clin Pediatr Endocrinol 25:71–76, 2016, PMC4860518).

At the age of 1 year, he was diagnosed with central diabetes insipidus, and treatment with desmopressin was started at 11 years old. At the age of 2 years, an arginine challenge test revealed severe growth hormone (GH) deficiency. GH replacement therapy was not performed at his guardian’s request. He developed insulin-resistant diabetes at the age of 26 years. Family history showed one degree of obesity in both parents (Fig. 4).

Fig. 4  Family tree of the patient. The family tree indicates that first-degree obesity was observed in the patient’s parents and siblings, but no definite endocrine disorders were identified.

On current admission, his height was 167.0 cm, body weight was 119.1 kg, BMI was 42.2 kg/m², body fat percentage was 42.5% measured by Inbody720 (InBody Japan Inc., Tokyo, Japan), abdominal circumference was 124 cm, blood pressure was 140/89 mmHg, and pulse rate was 55/min. He had no edema or notable abnormalities in the chest or abdomen to suggest excessive body fluid. He was medicated with linagliptin 5 mg, repaglinide 1 mg, azilsartan 20 mg, nifedipine 40 mg, azosemide 30 mg, and rosuvastatin 2.5 mg each day. Fat was highly accumulated both subcutaneously and viscerally (Fig. 5), but there was no other particular abnormality of fat distribution.

Fig. 5  Abdominal CT. Left: plain abdominal CT. Right: subcutaneous fat area (blue): 432.28 cm² and visceral fat area (red): 174.59 cm² are highlighted.

Laboratory findings revealed dyslipidemia and renal dysfunction (Table 1). Pituitary magnetic resonance imaging (MRI) showed empty sella and reduction of T1 high-intensity signal in the posterior lobe (Fig. 6). A slight but residual arginine vasopressin response with increased serum osmolality was shown on 5% hypertonic saline loading test. Together with MRI findings, we diagnosed partial central diabetes insipidus (Fig. 7). A GHRP-2 loading test resulted in additional diagnosis of severe GH deficiency (Fig. 8A). The insulin loading test revealed a normal response of ACTH, while the CRH loading test showed decreased peak levels of evoked cortisol. These findings suggest that hypoadrenocorticism can be due to primary cortisol insufficiency (Figs. 8B and 9). Central hypogonadism was diagnosed based on delayed LH and FSH responses in the GnRH load test in addition to decreased free testosterone secretion (Fig. 8C). Central hypothyroidism was not observed in the TRH load test (Fig. 8D). Abnormal eating behavior was indicated by the Eating Behavior Questionnaire [10], showing abnormal thinking and eating behavior in all items compared with controls, a result consistent with hypothalamic disorder (Fig. 10). In addition, the patient had cognitive impairment with an intelligence quotient of 58. The treatment for obesity was mainly diet and exercise therapy, but the patient had difficulty addressing his abnormal eating behavior. He began dialysis at the age of 41 years due to chronic kidney disease, which was possibly caused by his obesity and diabetes. He died at the age of 49 years due to bacterial pneumonia.

Table 1 Laboratory Data on Admission

Urinary Data		Reference Range	Biochemical data/Immunology		Reference Range
pH	5.5	5.0–8.0	K	4.6 mEq/L	3.6–5.0
Prot	4+	—	Cl	110 mEq/L	98–107
Glu	±	—	FPG	108 mg/dL	70–109
Osm	216 mOsm/L	<850	HbA1c	6.2%	4.6–6.2
Blood Count/Biochemical data			TG	210 mg/dL	50–149
WBC	5,220/μL	3,500–9,100	HDL-C	55 mg/dL	40–96
neutrophil	3,260/μL		LDL-C	112 mg/dL	70–139
lymphocyte	1,480/μL		CRP	0.12 mg/dL	≤0.14
eosinophil	200/μL		sOsm	305 mOsm/L	276–292
basophil	20/μL		IRI	4.3 μU/mL	1.1–17
RBC	394 × 104/μL	376–500 × 104	CPR	2.5 ng/mL	1.1–3.3
Hb	10.8 g/dL	13.5–17.6	TPOAb	8.2 IU/mL	<3.3
Ht	30.9 %	33.4–44.9	TgAb	11.5 U/mL	<19.3
Plt	22.8 × 104/μL	13.0–36.9	GH	<0.1 ng/mL
TP	6.9 g/dL	6.7–8.3	IGF-Ⅰ	28 IU/mL	57–135
Alb	3.5 g/dL	3.8–5.2	PRL	33.1 ng/mL
GOT	16 U/L	10–40	LH	10.6 IU/mL
GPT	13 U/L	5–40	FSH	12.5 IU/L
LDH	300 U/L	124–222	Free Testosterone	6.7 pg/mL	7.7–21.6
CK	234 U/L	45–163	TSH	4.081 μIU/mL	0.61–4.23
UA	7.6 mg/dL	2.5–7.0	Free T3	2.16 pg/mL	2.52–4.06
BUN	51 mg/dL	8.0–22.0	Free T4	0.93 ng/dL	0.75–1.45
Cr	3.37 mg/dL	0.47–0.79	ACTH	35.6 pg/mL
eGFR	17.8 mL/min/1.73m2	≥60	Cortisol	10.0 μg/dL
Na	144 mEq/L	136–147	AVP	<0.8 pg/mL

Fig. 6  Pituitary MRI. (A) T1-weighted sagittal and (B) T2-weighted sagittal image.

Fig. 7  5% Hypertonic Saline Load Test.

Fig. 8  Pituitary provocation test. (A), (B), (C), and (D) represent the results after GHRP-2 (100 μg, i.v.), CRH (100 μg, i.v.), GnRH (100 μg, i.v.), and TRH (200 μg, i.v.) load, respectively.

Fig. 9  Insulin Tolerance Test. Blood glucose levels are 112 mg/dL at start and 48 mg/dL at nadir (60 min).

Fig. 10  Eating Behavior Diagram in the current patient (Left panel) and lean male control subjects (Right panel, N = 32, BMI: 22.2 ± 4.6 [mean ± SE] kg/m²).

Assessment of subcutaneous adipose tissue by electron microscopy

An abnormal hypertrophy of adipocytes could be a reason for the hypo-leptinemia despite the patient’s severe obesity, so we used electron microscopy to investigate the morphological characterization of subcutaneous adipose tissue (Fig. 11). The average cell diameter in the patient was 109.3 μm (range: 100–129.6 μm), smaller than that of the control obese patient (145.5 μm, range: 111.1–170.4 μm), but larger than that of lean subjects, whose primary adipocyte population measured 50–70 μm in diameter [11]. Furthermore, the patient’s adipocytes were shown to be in a dense population with relatively uniform sizes (standard deviation of cell diameter: 9.5 μm vs. 19.3 μm in the control obese patient). Compared with the control obese patient, patients with severe obesity demonstrated fewer very small adipocytes and fibroblast-like cell clusters, even when adipocytes were significantly enlarged. The adipocytes in the current case may therefore be smaller than expected based on BMI, suggesting the involvement of some kind of adipocyte hypertrophy disorder.

Fig. 11  Electronic microscopy of subcutaneous fat of current patient (BMI: 41.5 kg/m²) and BMI matched control subject (BMI: 42 kg/m²).

Genetic analysis

The phenotype of the current patient was severe obesity, abnormal eating behavior, impaired intelligence, partial central diabetes insipidus, severe growth hormone deficiency, hypoadrenocorticism, and central hypogonadism. We suspected the involvement of central hereditary obesity and performed genetic assessment. The first step was to determine the genetic basis of the hypothalamic disorder and severe hypogonadism. As the patient had hypothalamic disorder and severe obesity, we examined whether he had Prader-Willi syndrome. There was absence of accompanying clinical symptoms such as hypotonia in the neonatal period, and there was no delayed onset of walking in infancy. The whole exome genome sequence showed no deletions or duplications in chromosome 15. Next, owing to various impairments in pituitary function, we suspected and examined the involvements of leptin gene abnormalities. Although deletions in intron area could not be detected by the whole exome analysis, no abnormalities were found in leptin gene. Similarly, there was no abnormality in the leptin receptor gene or its splicing abnormality in mRNA extracted from the patient’s leukocytes. Furthermore, there were no genetic abnormalities in factors involved in the regulation of energy metabolism, such as POMC, PC1, and MC4-R.

Discussion

In this study, to confirm the existence of subjects with severe obesity and hypo-leptinemia, we first carefully estimated the relationship between BMI and serum leptin concentrations. Among the target subjects, we focused on a case of severe obesity that was probably due to hypothalamic involvement with congenital central hypopituitarism and hypo-leptinemia. The patient did not have abnormality of leptin-related genes. We presented the detailed characteristics by comparing the control subjects.

Since our patient’s death, there has been an advance in drug therapy for obesity including incretin-based therapy. Leptin replacement could be a fundamental treatment for severe obesity with hypo-leptinemia, as in the current case. Leptin levels generally show a good positive correlation with the degree of obesity. However, there could be some cases of severe obesity with hypo-leptinemia, as we demonstrated in current study. Leptin replacement could theoretically be a fundamental therapy for such patients, so knowledge and understanding of these cases is suggested to be warranted.

Some cases of obesity are associated with a leptin deficiency relative to body weight, which may lead to decreased appetite suppression resulting in increased appetite, which in turn leads to weight gain. Since the first report of the dramatic effect of leptin replacement in obese patients lacking leptin activity due to a mutation of leptin gene [12], many studies in obese patients with leptin gene abnormalities have provided important insights into the biological properties and potential benefits of leptin, even beyond obesity [13]. Meanwhile, clinical trials of leptin in patients with simple obesity have not shown sufficient effects on weight loss in the physiological concentration range due to leptin resistance [7]. Recently, however, leptin has shown promising results in obese patients with relative leptin depression. A post-hoc pooled analysis of four trials in 1,064 subjects with BMI 27.0–40.0 kg/m² found that metreleptin, a leptin analog, was effective in reducing body weight among a subgroup with lower baseline leptin levels [14]. Based on these results, we suggest that leptin supplementation or the use of leptin analogs might have contributed to the improvement of the condition in the current case as well. Further studies are needed to accumulate more insight into severe obesity with relative hypo-leptinemia.

The summarized genotypic and clinical characteristics of representative non-syndromic and syndromic obesity caused by genetic impairments are presented in Table 2 [12, 15-25]. Hypo-leptinemia is rarely reported, except in cases of leptin deficiency due to Lep gene mutations, which are often associated with hypothalamic hypopituitarism. Regarding our patient’s low IQ, cognitive impairment could be secondarily linked to conditions such as hypoglycemia, early childhood hypothyroxinemia, and growth hormone deficiency, all of which may result from congenital pituitary hormone deficiencies [26, 27]. Additionally, basic research on leptin-deficient mice has demonstrated adverse effects on brain development and memory function [28], and some patients with leptin deficiency have indeed shown cognitive dysfunction [29]. Conversely, intellectual impairment is not consistently observed in patients with leptin deficiency or leptin receptor abnormalities [12, 15, 16]. These findings suggest a potential causal relationship between hypothalamic-pituitary dysfunction and the low IQ observed in this case.

Table 2 Genotypic and clinical characteristics of representative non-syndromic and syndromic obesity

Deficiency/syndrome	Casual gene/chromosomal area	Type of inheritance	Clinical features	Reference
Non-syndromic monogenic obesity
Leptin deficiency	LEP/7q31.3	AR	Hypo-leptinemia, Severe early-onset obesity, Intense, Hyperphagia, Hyperinsulinemia, Advanced bone-age, Hypogonadotropic, Hypogonadism	[12] [15] [16]
Leptin receptor deficiency	LEPR/1p31	AR	Hyperleptinemia, Early-onset morbid obesity, Hypogonadotropic hypogonadism, Inadequate secretion of growth hormone, Hypothalamic hypothyroidism	[16] [17]
Syndromic monogenic obesity
Prader-Willi syndrome	SNRPN, NDN, MAGEL2, MKRN3, etc./15q11.2-q13	Sporadic (65–75% paternal deletion, 20–30% maternal UPD, 1–3% imprinting defect)	Hypotonia, Developmental disability, Hyperphagia and obesity, Dysmorphic features, Behavioral and psychiatric disturbance, Hypogonadism, Short stature and growth hormone deficiency	[18] [19] [20] [21]
Bardet-Biedl/Laurence-Moon-Bardet-Biedl syndrome	BBS1-24, SCLT1, etc./Multiple locus	AR	Retinal cone-rod dystrophy, Central obesity, Postaxial polydactyly, Cognitive impairment, Hypogonadism, Genitourinary abnormalities, Kidney disease	[22] [23]
Alstom syndrome	ALMS1/2q13.1	AR	Childhood obesity associated with hyperinsulinemia, Chronic hyperglycemia and neurosensory deficits	[24] [25]

Regarding the relationship between serum leptin levels and pituitary function, our hypothesis is as follows: As shown in Fig. 1, the serum leptin levels in lean subjects (BMI: approximately 25 kg/m²) are almost identical to those of the current patient. Since most of these individuals exhibit no deficits in pituitary functions, including HPA, GH, and gonadotropin axes, it is conceivable that the effects of hypo-leptinemia in this patient are limited and that other factors may have contributed.

Another point of current case is that electron microscopic images of subcutaneous adipose tissue revealed relatively small adipocytes compared with a BMI-matched patient. The morphologic change in adipocytes could be due to secondary effects of diverse physiological or environmental factors, but some cases also could be due to the dysfunction of adipocyte itself. For example, a recent report provided clear evidence that HSP47, a collagen-specific chaperone, serves as a molecular mechanism for proper fat tissue expansion and its association with systemic energy balance [30]. As smaller adipocyte size affects the secretion of other adipocytokines, we preliminarily measured serum adiponectin levels and found that they were elevated compared with those of twenty male control patients with obesity (data not shown). Regarding chronic inflammatory markers, the high-sensitivity CRP level was not elevated (Table 1). Additionally, ectopic fat accumulation, indicated by fatty liver and associated with insulin resistance in our case, could be related to reduced adipocyte storage capacity due to impaired adipocyte hypertrophy. Further molecular investigations into proper fat tissue expansion are warranted to clarify the relationship between leptin and systemic energy balance.

Eating behaviors in Japanese obese individuals were recently investigated using the Eating Behavior Questionnaire [31]. Scores were generally higher in most sections for obese subjects compared to lean ones, although differences in the eating style score were relatively minor. In contrast, in our case, the eating style score was remarkably high, which may represent a unique characteristic.

Some cases of human obesity can be associated with low leptin levels relative to body weight. In such conditions, leptin replacement or leptin analogs may be useful, but there are limited such cases in the literature. We presented the case to demonstrate the various investigations, which could be important in the understanding of the characteristics of these conditions. Our patient had abnormalities in adipocyte and fatty fluid factor secretion, suggesting the possibility that dysfunction of adipocytes themselves, unknown genetic mutations, or developmental abnormalities in the hypothalamus may have been affected by something, although the definitive cause(s) of diseases could not be determined in current case. This study suggests that it may be useful to consider the indication of leptin-replacement, resistant to or even rather than conventional weight-loss strategies, for the patients with obesity with hypo-leptinemia (Graphical Abstract).

Graphical Abstract  There could be a population of obesity with hypo-leptinemia, which may create decrease in appetite suppression leading to increased appetite, which in turn leads to weight gain. In this study, we first investigated the serum leptin levels and their correlation with BMI to identify the subjects with relative hypo-leptinemia. Among them, we further investigated a unique patient with congenital central hypopituitarism by comparing his clinical and pathological characteristics with those of control subjects, showing morphological abnormality of adipocytes without definite genetic abnormalities. This study could contribute to ongoing discussions on personalized treatment approaches for obesity, and could offer insights into the potential use of leptin replacement therapy in similar cases, particularly resistance to conventional weight-loss strategies.

Declarations

Taka-aki Matsuoka is a member of Endocrine Journal’s Editorial Board.

Ethics Approval and Consent to Participate

This study was approved by Wakayama Medical University Research Ethics Committee (Approval #1328 for the measurement of serum leptin levels and #1363 for the study of electron microscope). Informed consent was obtained from all the subjects. All procedures followed were in accordance with the Helsinki Declaration.

Consent for Publication

Written informed consent was obtained from the patient for publication of this case report and all accompanying images.

Availability of Data and Materials

The datasets used and analyzed during the current study are available from the corresponding author upon reasonable request.

Competing Interests

The authors declare that they have no competing interests.

Funding

Not applicable.

Author Contributions

MK was the lead clinician in management of the patient and wrote the manuscript. SU and HA were clinicians in management of the patient. MK, SM, HA, TT, SU, KT, HI, TM revised and edited the manuscript. All authors approved the final submitted version. MK and SM contributed equally to this work.

Acknowledgments

We acknowledge proofreading and editing by Benjamin Phillis at the Clinical Study Support Center at Wakayama Medical University.

References

• 1   Banegas  JR,  López-García  E,  Graciani  A,  Guallar-Castillón  P,  Gutierrez-Fisac  JL, et al. (2007) Relationship between obesity, hypertension and diabetes, and health-related quality of life among the elderly. Eur J Cardiovasc Prev Rehabil 14: 456–462.
• 2   De Lorenzo  A,  Gratteri  S,  Gualtieri  P,  Cammarano  A,  Bertucci  P, et al. (2019) Why primary obesity is a disease? J Transl Med 17: 169.
• 3   Friedman  JM,  Halaas  JL (1998) Leptin and the regulation of body weight in mammals. Nature 395: 763–770.
• 4   Hosoda  K,  Masuzaki  H,  Ogawa  Y,  Miyawaki  T,  Hiraoka  J, et al. (1996) Development of radioimmunoassay for human leptin. Biochem Biophys Res Commun 221: 234–239.
• 5   Farooqi  S,  O’Rahilly  S (2006) Genetics of obesity in humans. Endocr Rev 27: 710–718.
• 6   Tanaka  T,  Kusakabe  T,  Ebihara  K,  Aizawa-Abe  M,  Aotani  D, et al. (2021) Practice guideline for lipodystrophy syndromes-clinically important diseases of the Japan Endocrine Society (JES). Endocr J 68: 1027–1042.
• 7   Heymsfield  SB,  Greenberg  AS,  Fujioka  K,  Dixon  RM,  Kushner  R, et al. (1999) Recombinant leptin for weight loss in obese and lean adults: a randomized, controlled, dose-escalation trial. JAMA 282: 1568–1575.
• 8   Matsuno  S,  Furuta  H,  Kosaka  K,  Doi  A,  Yorifuji  T, et al. (2019) Identification of a variant associated with early-onset diabetes in the intron of the insulin gene with exome sequencing. J Diabetes Investig 10: 947–950.
• 9   Isojima  T,  Kato  N,  Ito  Y,  Kanzaki  S,  Murata  M (2016) Growth standard charts for Japanese children with mean and standard deviation (SD) values based on the year 2000 national survey. Clin Pediatr Endocrinol 25: 71–76.
• 10   Inoue  K,  Maeda  N,  Kashine  S,  Fujishima  Y,  Kozawa  J, et al. (2011) Short-term effects of liraglutide on visceral fat adiposity, appetite, and food preference: a pilot study of obese Japanese patients with type 2 diabetes. Cardiovasc Diabetol 10: 109.
• 11   Verboven  K,  Wouters  K,  Gaens  K,  Hansen  D,  Bijnen  M, et al. (2018) Abdominal subcutaneous and visceral adipocyte size, lipolysis and inflammation relate to insulin resistance in male obese humans. Sci Rep 8: 4677.
• 12   Montague  CT,  Farooqi  IS,  Whitehead  JP,  Soos  MA,  Rau  H, et al. (1997) Congenital leptin deficiency is associated with severe early-onset obesity in humans. Nature 387: 903–908.
• 13   Farooqi  IS,  Matarese  G,  Lord  GM,  Keogh  JM,  Lawrence  E, et al. (2002) Beneficial effects of leptin on obesity, T cell hyporesponsiveness, and neuroendocrine/metabolic dysfunction of human congenital leptin deficiency. J Clin Invest 110: 1093–1103.
• 14   Depaoli  A,  Long  A,  Fine  G,  Stewart  M,  O’Rahilly  S (2018) Efficacy of metreleptin for weight loss in overweight and obese adults with low leptin levels. Program of 78th scientific sessions of American Diabetes Association (Abstract). Diabetes 67 (Suppl 1): 296-LB.
• 15   Farooqi  IS (2005) Genetic and hereditary aspects of childhood obesity. Best Pract Res Clin Endocrinol Metab 19: 359–374.
• 16   Besci  Ö,  Fırat  SN,  Özen  S,  Çetinkaya  S,  Akın  L, et al. (2023) A national multicenter study of leptin and leptin receptor deficiency and systematic review. J Clin Endocrinol Metab 108: 2371–2388.
• 17   Clément  K,  Vaisse  C,  Lahlou  N,  Cabrol  S,  Pelloux  V, et al. (1998) A mutation in the human leptin receptor gene causes obesity and pituitary dysfunction. Nature 392: 398–401.
• 18   Cassidy  SB,  Schwartz  S,  Miller  JL,  Driscoll  DJ (2012) Prader-Willi syndrome. Genet Med 14: 10–26.
• 19   Jong  MT,  Gray  TA,  Ji  Y,  Glenn  CC,  Saitoh  S, et al. (1999) A novel imprinted gene, encoding a RING zinc-finger protein, and overlapping antisense transcript in the Prader-Willi syndrome critical region. Hum Mol Genet 8: 783–793.
• 20   Schaaf  CP,  Gonzalez-Garay  ML,  Xia  F,  Potocki  L,  Gripp  KW, et al. (2013) Truncating mutations of MAGEL2 cause Prader-Willi phenotypes and autism. Nat Genet 45: 1405–1408.
• 21   Donlon  TA,  Lalande  M,  Wyman  A,  Bruns  G,  Latt  SA (1986) Isolation of molecular probes associated with the chromosome 15 instability in the Prader-Willi syndrome. Proc Natl Acad Sci U S A 83: 4408–4412.
• 22   Florea  L,  Caba  L,  Gorduza  EV (2021) Bardet-Biedl syndrome-multiple kaleidoscope images: insight into mechanisms of genotype-phenotype correlations. Genes (Basel) 12: 1353.
• 23   Dollfus  H,  Lilien  MR,  Maffei  P,  Verloes  A,  Muller  J, et al. (2024) Bardet-Biedl syndrome improved diagnosis criteria and management: Inter European Reference Networks consensus statement and recommendations. Eur J Hum Genet 32: 1347–1360.
• 24   Collin  GB,  Marshall  JD,  Ikeda  A,  So  WV,  Russell-Eggitt  I, et al. (2002) Mutations in ALMS1 cause obesity, type 2 diabetes and neurosensory degeneration in Alström syndrome. Nat Genet 31: 74–78.
• 25   Piñeiro-Gallego  T,  Cortón  M,  Ayuso  C,  Baiget  M,  Valverde  D (2012) Molecular approach in the study of Alström syndrome: analysis of ten Spanish families. Mol Vis 18: 1794–1802.
• 26   Brown  K,  Rodgers  J,  Johnstone  H,  Adams  W,  Clarke  M, et al. (2004) Abnormal cognitive function in treated congenital hypopituitarism. Arch Dis Child 89: 827–830.
• 27   Maruff  P,  Falleti  M (2005) Cognitive function in growth hormone deficiency and growth hormone replacement. Horm Res 64 Suppl 3: 100–108.
• 28   Fernandes  C,  Forny-Germano  L,  Andrade  MM,  Lyra  ESNM,  Ramos-Lobo  AM, et al. (2024) Leptin receptor reactivation restores brain function in early-life Lepr-deficient mice. Brain 147: 2706–2717.
• 29   Paz-Filho  GJ,  Babikian  T,  Asarnow  R,  Delibasi  T,  Esposito  K, et al. (2008) Leptin replacement improves cognitive development. PLoS One 3: e3098.
• 30   Shin  J,  Toyoda  S,  Okuno  Y,  Hayashi  R,  Nishitani  S, et al. (2023) HSP47 levels determine the degree of body adiposity. Nat Commun 14: 7319.
• 31   Saito  M,  Usui  I,  Sugawara  N,  Jojima  T,  Sakurai  S, et al. (2024) Patients with diabetes and obesity exhibit characteristics in eating and coping behaviors and personality traits. Diabetol Int 15: 528–534.

Abbreviations

GH

growth hormone

MRI

Magnetic resonance imaging