INSR-related severe syndromic insulin resistance comprises a phenotypic spectrum that is a continuum from the severe phenotype Donohue syndrome (DS) (also known as leprechaunism) to the milder phenotype Rabson-Mendenhall syndrome (RMS). DS at the severe end of the spectrum is characterized by severe insulin resistance (hyperinsulinemia with associated fasting hypoglycemia and postprandial hyperglycemia), severe prenatal growth restriction and postnatal growth failure, hypotonia and developmental delay, characteristic facies, and organomegaly involving heart, kidneys, liver, spleen, and ovaries. Death usually occurs before age one year. RMS at the milder end of the spectrum is characterized by severe insulin resistance that, although not as severe as that of DS, is nonetheless accompanied by fluctuations in blood glucose levels, diabetic ketoacidosis, and – in the second decade – microvascular complications. Findings can range from severe growth delay and intellectual disability to normal growth and development. Facial features can be milder than those of DS. Complications of longstanding hyperglycemia are the most common cause of death. While death usually occurs in the second decade, some affected individuals live longer.

INSR-related severe syndromic insulin resistance comprises a phenotypic spectrum that is a continuum from the severe phenotype Donohue syndrome (DS) (also known as leprechaunism) to the milder phenotype Rabson-Mendenhall syndrome (RMS). DS at the severe end of the spectrum is characterized by severe insulin resistance (hyperinsulinemia with associated fasting hypoglycemia and postprandial hyperglycemia), severe prenatal growth restriction and postnatal growth failure, hypotonia and developmental delay, characteristic facies, and organomegaly involving heart, kidneys, liver, spleen, and ovaries. Death usually occurs before age one year. RMS at the milder end of the spectrum is characterized by severe insulin resistance that, although not as severe as that of DS, is nonetheless accompanied by fluctuations in blood glucose levels, diabetic ketoacidosis, and – in the second decade – microvascular complications. Findings can range from severe growth delay and intellectual disability to normal growth and development. Facial features can be milder than those of DS. Complications of longstanding hyperglycemia are the most common cause of death. While death usually occurs in the second decade, some affected individuals live longer.

Congenital isolated adrenocorticotropic hormone deficiency (IAD) is characterized by severe hypoglycemia in the neonatal period, associated with seizures in about half of cases, prolonged cholestatic jaundice, and very low plasma ACTH levels with no significant response to corticotropin-releasing hormone (CRH; 122560). Plasma cortisol levels are also extremely low (Vallette-Kasic et al., 2005). TBX19 is required for initiation of transcription of the POMC gene (176830), which produces the precursor peptide from which ACTH is derived (Lamolet et al., 2001).

Glycogen storage disease type 0 (also known as GSD 0) is a condition caused by the body's inability to form a complex sugar called glycogen, which is a major source of stored energy in the body. GSD 0 has two types: in muscle GSD 0, glycogen formation in the muscles is impaired, and in liver GSD 0, glycogen formation in the liver is impaired.\n\nThe signs and symptoms of muscle GSD 0 typically begin in early childhood. Affected individuals often experience muscle pain and weakness or episodes of fainting (syncope) following moderate physical activity, such as walking up stairs. The loss of consciousness that occurs with fainting typically lasts up to several hours. Some individuals with muscle GSD 0 have a disruption of the heart's normal rhythm (arrhythmia) known as long QT syndrome. In all affected individuals, muscle GSD 0 impairs the heart's ability to effectively pump blood and increases the risk of cardiac arrest and sudden death, particularly after physical activity. Sudden death from cardiac arrest can occur in childhood or adolescence in people with muscle GSD 0.\n\nIndividuals with liver GSD 0 usually show signs and symptoms of the disorder in infancy. People with this disorder develop low blood sugar (glucose), known as hypoglycemia, after going long periods of time without food (fasting). Signs of hypoglycemia become apparent when affected infants begin sleeping through the night and stop late-night feedings; these infants exhibit extreme tiredness (lethargy), pale skin (pallor), and nausea. During episodes of fasting, ketone levels in the blood may increase (ketosis). Ketones are molecules produced during the breakdown of fats, which occurs when stored sugars (such as glycogen) are unavailable. These short-term signs and symptoms of liver GSD 0 often improve when food is eaten and glucose levels in the body return to normal. The features of liver GSD 0 vary; they can be mild and go unnoticed for years, or they can include developmental delay and growth failure.

Dicarboxylic aminoaciduria (DCBXA) is characterized by a striking excretion of urinary glutamate and aspartate, resulting from the incomplete reabsorption of anionic amino acids from the glomerular filtrate in the kidney. Patients may have impaired intellectual development (summary by Bailey et al., 2011).

Phosphorylase kinase (PhK) deficiency causing glycogen storage disease type IX (GSD IX) results from deficiency of the enzyme phosphorylase b kinase, which has a major regulatory role in the breakdown of glycogen. The two types of PhK deficiency are liver PhK deficiency (characterized by early childhood onset of hepatomegaly and growth restriction, and often, but not always, fasting ketosis and hypoglycemia) and muscle PhK deficiency, which is considerably rarer (characterized by any of the following: exercise intolerance, myalgia, muscle cramps, myoglobinuria, and progressive muscle weakness). While symptoms and biochemical abnormalities of liver PhK deficiency were thought to improve with age, it is becoming evident that affected individuals need to be monitored for long-term complications such as liver fibrosis and cirrhosis.

Glycogen storage disease type I (GSDI) is characterized by accumulation of glycogen and fat in the liver and kidneys resulting in hepatomegaly and nephromegaly. Severely affected infants present in the neonatal period with severe hypoglycemia due to fasting intolerance. More commonly, untreated infants present at age three to four months with hepatomegaly, severe hypoglycemia with or without seizures, lactic acidosis, hyperuricemia, and hypertriglyceridemia. Affected children typically have doll-like faces with full cheeks, relatively thin extremities, short stature, and a protuberant abdomen. Xanthoma and diarrhea may be present. Impaired platelet function and development of reduced or dysfunctional von Willebrand factor can lead to a bleeding tendency with frequent epistaxis and menorrhagia in females. Individuals with untreated GSDIb are more likely to develop impaired neutrophil and monocyte function as well as chronic neutropenia resulting in recurrent bacterial infections, gingivitis, periodontitis, and genital and intestinal ulcers. Long-term complications of untreated GSDI include short stature, osteoporosis, delayed puberty, renal disease (including proximal and distal renal tubular acidosis, renal stones, and renal failure), gout, systemic hypertension, pulmonary hypertension, hepatic adenomas with potential for malignancy, pancreatitis, and polycystic ovaries. Seizures and cognitive impairment may occur in individuals with prolonged periods of hypoglycemia. Normal growth and puberty are expected in treated children. Most affected individuals live into adulthood.

Hypoinsulinemic hypoglycemia and body hemihypertrophy is a rare, genetic, endocrine disease characterized by neonatal macrosomia, asymmetrical overgrowth (typically manifesting as left-sided hemihypertrophy) and recurrent, severe hypoinsulinemic (or hypoketotic hypo-fatty-acidemic) hypoglycemia in infancy, which results in episodes of reduced consciousness and seizures.

Fanconi-Bickel syndrome is a rare but well-defined clinical entity, inherited in an autosomal recessive mode and characterized by hepatorenal glycogen accumulation, proximal renal tubular dysfunction, and impaired utilization of glucose and galactose (Manz et al., 1987). Because no underlying enzymatic defect in carbohydrate metabolism had been identified and because metabolism of both glucose and galactose is impaired, a primary defect of monosaccharide transport across the membranes had been suggested (Berry et al., 1995; Fellers et al., 1967; Manz et al., 1987; Odievre, 1966). Use of the term glycogenosis type XI introduced by Hug (1987) is to be discouraged because glycogen accumulation is not due to the proposed functional defect of phosphoglucomutase, an essential enzyme in the common degradative pathways of both glycogen and galactose, but is secondary to nonfunctional glucose transport.

Silver-Russell Syndrome (SRS) is typically characterized by asymmetric gestational growth restriction resulting in affected individuals being born small for gestational age, with relative macrocephaly at birth (head circumference =1.5 SD above birth weight and/or length), prominent forehead usually with frontal bossing, and frequently body asymmetry. This is followed by postnatal growth failure, and in some cases progressive limb length discrepancy and feeding difficulties. Additional clinical features include triangular facies, fifth-finger clinodactyly, and micrognathia with narrow chin. Except for the limb length asymmetry, the growth failure is proportionate and head growth normal. The average adult height in untreated individuals is ~3.1±1.4 SD below the mean. The Netchine-Harbison Clinical Scoring System (NH-CSS) is a sensitive diagnostic scoring system. Clinical diagnosis can be established in an individual who meets at least four of the NH-CSS clinical criteria – prominent forehead/frontal bossing and relative macrocephaly at birth plus two additional findings – and in whom other disorders have been ruled out.

Cytosolic phosphoenolpyruvate carboxykinase deficiency causes a defect in gluconeogenesis that results in a 'biochemical signature' of fasting hypoglycemia with high tricarboxylic acid cycle intermediate excretion, particularly of fumarate. Other biochemical anomalies that may be seen during metabolic crisis include ketonuria, dicarboxylic aciduria, and urea cycle dysfunction (Vieira et al., 2017). See PCKDM (261650) for a discussion of mitochondrial PCK (PEPCK2; 614095) deficiency.