Inborn Errors of Ketogenesis: Novel Variants, Clinical Presentation, and Follow-Up in a Series of Four Patients

Inborn errors of ketogenesis are rare disorders that result in acute and fulminant decompensation during lipolytic stress, particularly in infants and children. These include mitochondrial 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase (HMGCS) deficiency and HMG-CoA lyase (HMGCL) deficiency. In this series, we describe the clinical, biochemical, and molecular profiles of four patients along with dietary interventions and their outcomes on a long-term follow-up. Two patients each of HMGCS and HMGCL deficiency were evaluated with clinical history, biochemical investigations, including tandem mass spectrometry (TMS) and urine gas chromatography-mass spectrometry (GCMS). Molecular analysis was performed by whole-exome sequencing, as well as exon array validated by long-range polymerase chain reaction. All individuals were diagnosed with acute metabolic decompensation in the early infancy period except one with HMGCL deficiency who had the first presentation at 5 years of age. Central nervous system manifestations, severe metabolic acidosis, hyperammonemia, hypoglycemia with a normal lactate, and absence of urinary ketones were observed in all the affected individuals. The disorder was life-threatening in three individuals and one succumbed to the illness. TMS was nonspecific and urine GCMS revealed dicarboxylic aciduria in HMGCS deficiency. Both the patients with HMGCL deficiency demonstrated elevated 3 hydroxyisovaleryl carnitine levels in TMS and metabolites of leucine degradation in urine GCMS. We identified five novel variants that included a large deletion involving exon 2 in HMGCL gene. There was no evidence of long-term neurological sequelae in the living individuals. Diet with moderation of fat intake was followed in two individuals with HMGCS deficiency. Low leucine and protein diet with moderation of fat intake was followed in the individual with HMGCL deficiency. All affected individuals are thriving well with no further major metabolic decompensation.

A Young Female With Medium-Chain Acyl-CoA Dehydrogenase Deficiency (MCADD): A Case Report

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency (MCADD) is a rare autosomal recessive inborn error of mitochondrial fatty acid oxidation. MCAD is essential for fatty acid β-oxidation during hepatic ketogenesis, which provides a major source of energy once hepatic glycogen stores are exhausted during extended fasting and periods of increased energy demand. The inability to metabolize these fatty acids results in hypoketotic hypoglycemia and the accumulation of toxic partially metabolized fatty acids. Intercurrent infection, extended fasting, excessive alcohol intake, vomiting, or diarrhea can lead to serious illness, including encephalopathy and even sudden death. Young people with MCADD are followed up on a regular basis by their metabolic disease specialist, and they are informed about risk factors as they advance through adolescence and adulthood. They should also carry along a written emergency management plan and relevant contact numbers. We describe a case of a 17-year-old female who attended her local emergency care center complaining of severe abdominal pain, vomiting, muscle ache, and poor oral intake. She was known to have MCADD; however, her emergency care plan had a date from eight years ago. She made a rapid recovery after receiving intravenous glucose and other therapies. The patient's concerns and knowledge about MCADD were not fully appreciated at the initial stage due to the rare nature of the disease. This in combination with the absence of current notes on the system, an emergency care plan dated from eight years ago, and the need to obtain specialist advice led to a slight delay in commencing specific therapy. This case report serves as a reminder of the emergency presentation of young people with MCADD, emphasizing the importance of effective communication between the patient, their parents, and the treating clinicians, obtaining the emergency care plan and recommendations, and communicating with the metabolic disease specialist.

Hereditary Tyrosinemia Compounded With Hyperinsulinemic Hypoglycemia: Challenging Diagnosis of a Rare Case

Hereditary tyrosinemia type 1 (HT-1) is a rare autosomal recessive disorder caused by a deficiency in the enzyme fumarylacetoacetate hydrolase (FAH), which catalyzes the final step in the tyrosine degradation pathway. Hereditary tyrosinemia is a heterogeneous disease with a wide spectrum of clinical manifestations involving hepatic, renal, or nervous systems. It has grave consequences if left untreated. Some of the late complications of hereditary tyrosinemia include cirrhosis, liver nodules, hepatocellular carcinoma, hypophosphatemic rickets, nephrocalcinosis, glomerulosclerosis, and chronic renal failure. Rarely, infants with hereditary tyrosinemia may present with persistent hypoglycemia, which may be a result of acute liver failure or hyperinsulinism. Hyperinsulinemic hypoglycemia (HH), caused by dysregulation of insulin secretion from pancreatic β-cells, leads to insulin driven glucose entry into the tissues and inhibits glycolysis, gluconeogenesis, fatty acid release, and ketone body synthesis. Hyperinsulinemic hypoglycemia can cause severe, persistent hypoketotic hypoglycemia. Diagnosing tyrosinemia type 1 can be a challenge as it is a heterogeneous disorder with a wide variety of clinical manifestations and complications. We herein report a rare case of a three-day-old male neonate with HT-1 compounded with HH.

Fatty acid oxidation disorders

Fatty acid oxidation disorders (FAODs) are inborn errors of metabolism due to disruption of either mitochondrial β-oxidation or the fatty acid transport using the carnitine transport pathway. The presentation of a FAOD will depend upon the specific disorder, but common elements may be seen, and ultimately require a similar treatment. Initial presentations of the FAODs in the neonatal period with severe symptoms include cardiomyopathy, while during infancy and childhood liver dysfunction and hypoketotic hypoglycemia are common. Episodic rhabdomyolysis is frequently the initial presentation during or after adolescence; although, these symptoms may develop at any age for most of the FAODs The treatment of all FAOD's include avoidance of fasting, aggressive treatment during illness, and supplementation of carnitine, if necessary. The long-chain FAODs differ by requiring a fat-restricted diet and supplementation of medium chain triglyceride oil and often docosahexaenoic acid (DHA)-an essential fatty acid, crucial for brain, visual, and immune functions and prevention of fat soluble vitamin deficiencies. The FAOD are a group of autosomal recessive disorders associated with significant morbidity and mortality, but early diagnosis on newborn screening (NBS) and early initiation of treatment are improving outcomes. There is a need for clinical studies including randomized, controlled, therapeutic trials to continue to evaluate current understanding and to implement future therapies.