A Mutation in INSR in a Child Presenting with Severe Acanthosis Nigricans

Body Fat Distribution Contributes to Defining the Relationship between Insulin Resistance and Obesity in Human Diseases

The risk for metabolic and cardiovascular complications of obesity is defined by body fat distribution rather than global adiposity. Unlike subcutaneous fat, visceral fat (including hepatic steatosis) reflects insulin resistance and predicts type 2 diabetes and cardiovascular disease. In humans, available evidence indicates that the ability to store triglycerides in the subcutaneous adipose tissue reflects enhanced insulin sensitivity. Prospective studies document an association between larger subcutaneous fat mass at baseline and reduced incidence of impaired glucose tolerance. Case-control studies reveal an association between genetic predisposition to insulin resistance and a lower amount of subcutaneous adipose tissue. Human peroxisome proliferator-activated receptorgamma (PPAR-γ) promotes subcutaneous adipocyte differentiation and subcutaneous fat deposition, improving insulin resistance and reducing visceral fat. Thiazolidinediones reproduce the effects of PPAR-γ activation and therefore increase the amount of subcutaneous fat while enhancing insulin sensitivity and reducing visceral fat. Partial or virtually complete lack of adipose tissue (lipodystrophy) is associated with insulin resistance and its clinical manifestations, including essential hypertension, hypertriglyceridemia, reduced HDL-c, type 2 diabetes, cardiovascular disease, and kidney disease. Patients with Prader Willi syndrome manifest severe subcutaneous obesity without insulin resistance. The impaired ability to accumulate fat in the subcutaneous adipose tissue may be due to deficient triglyceride synthesis, inadequate formation of lipid droplets, or defective adipocyte differentiation. Lean and obese humans develop insulin resistance when the capacity to store fat in the subcutaneous adipose tissue is exhausted and deposition of triglycerides is no longer attainable at that location. Existing adipocytes become large and reflect the presence of insulin resistance.

Acanthosis Nigricans: An Updated Review

BACKGROUND

Early recognition of acanthosis nigricans is important because acanthosis nigricans can be a cutaneous manifestation of a variety of systemic disorders and, rarely, as a sign of internal malignancy.

OBJECTIVE

The purpose of this article is to familiarize pediatricians with the clinical manifestations, evaluation, diagnosis, and management of acanthosis nigricans.

METHODS

A search was conducted in November 2021in PubMed Clinical Queries using the key term "acanthosis nigricans". The search strategy included all clinical trials, observational studies, and reviews published within the past 10 years. Only papers published in the English literature were included in this review. The information retrieved from the above search was used in the compilation of the present article.

RESULTS

Acanthosis nigricans is characterized by symmetric, hyperpigmented, and velvety plaques with ill-defined borders, typically involving intertriginous areas. Obesity is the most common cause of acanthosis nigricans which is increasingly observed in obese children and adolescents and can serve as a cutaneous marker of insulin resistance. Early recognition of acanthosis nigricans is important because acanthosis nigricans can also be a cutaneous manifestation of a variety of systemic disorders and, rarely, as a sign of internal malignancy. This may consist of weight reduction, discontinuation of causative drugs, treatment of underlying endocrinopathy, or treatment of an underlying malignancy. For patients with isolated acanthosis nigricans and for those whose underlying cause is not amenable to treatment, treatment of the lesion may be considered for cosmetic reasons. Topical retinoids, vitamin D analogs, chemical peels, and other keratolytics are often used for the treatment of localized lesions. Seldom, systemic therapy such as oral retinoids may be considered for extensive or generalized acanthosis nigricans and acanthosis nigricans unresponsive to topical therapy. Other uncommon treatment modalities include dermabrasion, laser therapy, and surgical removal.

CONCLUSION

Although acanthosis nigricans is treatable, a complete cure is difficult to achieve. The underlying cause should be treated, if possible, to resolve and prevent the recurrence of acanthosis nigricans. The diagnosis is mainly clinical, based on the characteristic appearance (symmetrically distributed, hyperpigmented, velvety, papillomatous, hyperkeratotic plaques with ill-defined borders) and the typical sites (intertriginous areas, flexural area, and skin folds) of the lesions. The diagnosis might be difficult for lesions that have atypical morphology or are in an unusual location. Clinicians should be familiar with the clinical signs, evaluation, diagnosis, and therapy of acanthosis nigricans because of the link between it and underlying diseases.

Rabson-Mendenhall Syndrome in a brother-sister pair in Kuwait: Diagnosis and 5 year follow up

AIM

To report on Rabson-Mendenhall Syndrome (RMS) diagnosed in Kuwait.

METHODS

A toddler (18 months old) was referred with high plasma insulin and dysmorphic features suggestive of RMS including coarse facial features with globular nose, full lips and furrowed tongue. His skin was hyperkeratotic with hypertrichosis. His sister (aged 13.5 years) was diagnosed with diabetes at 9 years of age and treated with metformin and insulin. She presented with similar dysmorphic features, extensive acanthosis nigricans, dental abnormalities and bilateral nephrocalcinosis. The children were born to non-consanguineous parents. Blood samples were sent for genetic testing in a reference laboratory.

RESULTS

Both children were found to be homozygous for the p.Arg141Trp missense variant (p.Arg114Trp if numbered according to pro-receptor sequence) in the alpha subunit of the insulin receptor.

CONCLUSIONS

These cases demonstrate the importance of raising awareness among healthcare professionals to ensure rapid referral of patients with characteristic physical features of RMS and severe insulin resistance for genetic testing. Unfortunately, treatment of RMS patients remains a challenge with poor prognosis and short life expectancy usually caused by diabetes-related complications. Genetic testing confirms the diagnosis and allows informed genetic counseling of parents considering future pregnancies.

Two Novel Variants and One Previously Reported Variant in the Insulin Receptor Gene in Two Cases with Severe Insulin Resistance Syndrome

Donohue syndrome (DS) and Rabson-Mendenhall syndrome (RMS) are rare diseases caused by biallelic variants within the insulin receptor gene (INSR). Here, we report 2 cases: one with DS and the other with RMS. The case with DS presented with intrauterine growth retardation, nipple hypertrophy, clitoromegaly, distended abdomen, hypertrichosis, and dysmorphic features. The second case showed severe acanthosis nigricans, hyperkeratosis, and hypertrichosis. In both cases, abnormal glucose homeostasis due to severe insulin resistance was observed. The diagnosis of DS and RMS was established based on clinical characteristics, abnormal glucose homeostasis, high serum insulin levels, and determination of pathogenic variants in the INSR gene. The first case with DS has 2 novel homozygous variants, NM_000208.3, c.3122delA (p.N1041Mfs*16) and c.3419C>G (p.A1140G), and the second case with RMS has a previously reported homozygous variant NM_000208.3, c.3529+5G>A (IVS19+5G>A) in the INSR gene.

Insulin Receptor Trafficking: Consequences for Insulin Sensitivity and Diabetes

Insulin receptor (INSR) has been extensively studied in the area of cell proliferation and energy metabolism. Impaired INSR activities lead to insulin resistance, the key factor in the pathology of metabolic disorders including type 2 diabetes mellitus (T2DM). The mainstream opinion is that insulin resistance begins at a post-receptor level. The role of INSR activities and trafficking in insulin resistance pathogenesis has been largely ignored. Ligand-activated INSR is internalized and trafficked to early endosome (EE), where INSR is dephosphorylated and sorted. INSR can be subsequently conducted to lysosome for degradation or recycled back to the plasma membrane. The metabolic fate of INSR in cellular events implies the profound influence of INSR on insulin signaling pathways. Disruption of INSR-coupled activities has been identified in a wide range of insulin resistance-related diseases such as T2DM. Accumulating evidence suggests that alterations in INSR trafficking may lead to severe insulin resistance. However, there is very little understanding of how altered INSR activities undermine complex signaling pathways to the development of insulin resistance and T2DM. Here, we focus this review on summarizing previous findings on the molecular pathways of INSR trafficking in normal and diseased states. Through this review, we provide insights into the mechanistic role of INSR intracellular processes and activities in the development of insulin resistance and diabetes.