Effect of metformin and rosiglitazone in a prepubertal boy with Alström syndrome

Alström Syndrome: A Review Focusing on Its Diverse Clinical Manifestations and Their Etiology as a Ciliopathy

Alström syndrome is a form of inherited obesity caused by a single gene abnormality and is inherited as an autosomal recessive trait. It is characterised by a variety of clinical manifestations, including progressive visual and hearing impairment, type 2 diabetes mellitus, dilated cardiomyopathy, and hepatic and renal dysfunction, in addition to obesity. Recent insights underline the pivotal involvement of the disease-associated gene (ALMS1) in cilia formation and function, leading to the classification of its clinical manifestations as a ciliopathy. This review delineates the diverse clinical indicators defining the syndrome and elucidates its pathological underpinnings.

Acanthosis nigricans: To be or not to be afraid

Acanthosis nigricans (AN), a skin disorder with high prevalence, represents a dermatological condition with esthetic implications, but otherwise mild symptoms. For any clinician, it is in fact the tip of the iceberg, leading him/her to investigate what lies beneath the surface, since AN points to a systemic problem or disease: metabolic disorder (most frequently), endocrine syndrome, medication side effects, malignancy, and genetic factors. Sometimes, it is the first observed sign of a malignancy or of diabetes mellitus, especially in patients with chronic metabolic disorder; therefore, it is not to be taken lightly. The present review summarizes the information in literature regarding the etiopathogenesis of AN. We propose a new classification that aims to better organize the different types of AN, with implications on the extent and urgency of the investigation plan, as well as various therapeutic algorithms. Therapy options are also presented, both systemic treatments that target the underlying disease, and local ones for esthetic reasons.

Clinical, molecular genetics and therapeutic aspects of syndromic obesity

Obesity has become a major health problem worldwide. To date, more than 25 different syndromic forms of obesity are known in which one (monogenic) or multiple (polygenic) genes are involved. This review gives an overview of these forms and focuses more in detail on 6 syndromes: Prader Willi Syndrome and Prader Willi like phenotype, Bardet Biedl Syndrome, Alström Syndrome, Wilms tumor, Aniridia, Genitourinary malformations and mental Retardation syndrome and 16p11.2 (micro)deletions. Years of research provided plenty of information on the molecular genetics of these disorders and the obesity phenotype leading to a more individualized treatment of the symptoms, however, many questions still remain unanswered. As these obesity syndromes have different signs and symptoms in common, it makes it difficult to accurately diagnose patients which may result in inappropriate treatment of the disease. Therefore, the big challenge for clinicians and scientists is to more clearly differentiate all syndromic forms of obesity to provide conclusive genetic explanations and eventually deliver accurate genetic counseling and treatment. In addition, further delineation of the (functions of the) underlying genes with the use of array- or next-generation sequencing-based technology will be helpful to unravel the mechanisms of energy metabolism in the general population.

Alström Syndrome: Mutation Spectrum of ALMS1

Alström Syndrome (ALMS), a recessive, monogenic ciliopathy caused by mutations in ALMS1, is typically characterized by multisystem involvement including early cone-rod retinal dystrophy and blindness, hearing loss, childhood obesity, type 2 diabetes mellitus, cardiomyopathy, fibrosis, and multiple organ failure. The precise function of ALMS1 remains elusive, but roles in endosomal and ciliary transport and cell cycle regulation have been shown. The aim of our study was to further define the spectrum of ALMS1 mutations in patients with clinical features of ALMS. Mutational analysis in a world-wide cohort of 204 families identified 109 novel mutations, extending the number of known ALMS1 mutations to 239 and highlighting the allelic heterogeneity of this disorder. This study represents the most comprehensive mutation analysis in patients with ALMS, identifying the largest number of novel mutations in a single study worldwide. Here, we also provide an overview of all ALMS1 mutations identified to date.

Alström syndrome: insights into the pathogenesis of metabolic disorders

Genetic causes of obesity include the ciliopathies Alström syndrome and Bardet-Biedl syndrome. In these disorders, mutations cause dysfunction of the primary cilium, an organelle involved in intracellular and intercellular sensing and signaling. Alström syndrome is an autosomal-recessive disorder caused solely by mutations in ALMS1. By contrast, Bardet-Biedl syndrome is caused by mutations in at least 14 genes involved in primary cilium function. Despite equivalent levels of obesity, patients with Alström syndrome are more likely than those with Bardet-Biedl syndrome to develop childhood type 2 diabetes mellitus (T2DM), suggesting that ALMS1 might have a specific role in β-cell function and/or peripheral insulin signaling pathways. How mutations in genes that encode proteins involved in primary cilium function lead to the clinical phenotypes of these syndromes is being revealed by work in mutant mouse models. With the aid of these models, insights are being obtained into the pathogenic mechanisms that underlie obesity, insulin resistance and T2DM. Research into ciliopathies, including Alström syndrome and Bardet-Biedl syndrome, should lead not only to improved treatments for individuals with these genetic disorders, but also to improved understanding of the cellular pathways involved in other common causes of obesity and T2DM.

Combined occurrence of diabetes mellitus and retinitis pigmentosa

The combined occurrence of diabetes mellitus (DM) and retinitis pigmentosa (RP) is rare. It has been reported in the form of four different syndromes that are inherited in an autosomal recessive fashion. We describe two cases of DM and RP occurring together. The first case was a 35-year-old male who presented with insulin-treated diabetes, obesity, hypertension, polydactyly, normal cognitive functions, an ataxic gait, blindness secondary to RP, dyslipidemia, impaired renal function, and multiple renal cysts. He was diagnosed clinically as having Bardet-Biedl syndrome. The second case was a 34-year-old male who presented with insulin-resistant diabetes, hypertension, blindness secondary to RP, deafness, normal cognitive functions, primary infertility, renal, and liver impairment. He was diagnosed clinically as having Alström syndrome. Because of overlapping clinical manifestations and the cost and time involved in genetic studies, clinical criteria can be used for diagnosis and as a guide for genetic mapping in these patients.

New insights and therapies for the metabolic consequences of Alström syndrome

PURPOSE OF REVIEW

Recent studies have begun to evaluate the heterogeneity of insulin resistance in syndromes associated with type 2 diabetes, dyslipidaemia and associated cardiac, renal and hepatic consequences. These insights are of particular importance in Alström syndrome in which all of these conditions coexist from a young age with considerable morbidity and reduction in life expectancy. Clear definition of the phenotype in the syndrome may clarify biochemical pathways of crucial importance in propensity to diabetic complications and heart disease in the general population. This review will focus on ways in which more effective treatments can be put in place for Alström families from childhood and adolescence.

RECENT FINDINGS

Studies of body fat distribution, insulin resistance, glucose metabolism and dyslipidaemia in Alström syndrome will be discussed as well as genotypic and phenotypic variation in the syndrome in the context of recent metabolic studies in insulin resistance. Potential therapies including low-carbohydrate diet, niaspan and incretins will be considered.

SUMMARY

These new insights will encourage early introduction of protective nutrition, exercise and drug therapies in Alström syndrome and suggest novel approaches to understanding diabetes mellitus, hyperlipidaemias and heart disease in the general population.