HMG-CoA Lyase Deficiency: Biochemical Basis, Screening, And Treatment Options Essay.

Biochemical Basis of HMG-CoA Lyase Deficiency

You will research your selected Disease using Primary Literature, and Construct a written report that Describes the Disease’s Biochemical basis Compared to a Healthy Individualâ's Biochemistry, Methods of screening, and both Current and Future treatment Options.

HMG- CoA lyase deficiency also known as 3-hydroxy-3-methylglutaryl-CoA lyase deficiency is a disorder that is inherited and is not common¹. This disease was first explained by Faull in the year 1976 and it is reported that every 1 individual in 1, 00,000 is suffered by this disease^12. HMG- CoA lyase ( HL) is an enzyme that is present in the mitochondria and catalyzes the reaction in which HMG-CoA breaks down into acetyl CoA and acetocetate⁴. This is the finalstep of the ketogenesis process and catabolism of leucine.This disease involves a lack of processing an amino acid called as leucine in the mitochondria which helps in the formation of proteins¹⁴. In this disorder the body is also not able to make ketones in the liver which play an important role in providing energy by being used up in the body during fasting that is lack of food³. This disease is screened during the birth of the child. It leads to various symptoms such as lethargy, vomiting, low sugar in the blood also known as hypoglycemia, metabolic acidosis in which the toxic compounds combine together and increase the acidity of blood, infection and coma¹. This paper demonstrates the comparison of biochemical aspects of the patients suffering from HMG- CoA deficiency with the biochemical aspects of a healthy individual. It also demonstrates the methods of screening the disease and the current and the future treatment options.

According to the researchers, around 60-70% of the new born patients suffer from the deficiency of HMG CoA Lyase enzyme and around 30 % of the neonatal babies suffer during the period between 2^nd and 5^th day from the day they are born¹⁶. The patients also suffer from symptoms similar to Reye syndrome such as encelopathy, hepatomegaly and hyperammonemia.  A deficiency in the HMGCL gene leads to HMG-CoA lyase deficiency⁵. HMGCL gene plays an important role in  the formation of an enzyme 3-hydroxymethyl-3-methylglutaryl-coenzyme A lyase (HMG-CoA lyase) and also helps in the  processing of  leucine and breaking proteins and fats to provide energy to the body¹⁸. A decrease in the activity of HMG-CoA lyase occurs due to the mutation in the HMGCL gene and hence it becomes difficult for the body to process leucine and form ketones in a proper manner¹⁹. Due to the inability of processing of leucine, it results in the accumulation of different byproducts that are chemical in nature and can lead to metabolic acidosis. A lack of ketones leads to a low level of glucose in the blood of the patient which leads to a damage in the cell and the tissues specifically in the central nervous system⁷. A healthy individual has a HMG- CoA lyase enzyme that is encoded by the HMGCL gene that is present

Comparison of Biochemical Aspects of Patients with HMG-CoA Lyase Deficiency to a Healthy Individual

on chromosome number one¹⁹. The pancreas and the liver of the healthy individuals have the highest activity of HMG- CoA lyase enzyme. The pancreas has a high capacity of ketogenic activity and moderate activity in skeletal muscle and the testis. It helps in providing energy to the individuals and prevents hypoglycemia and metabolic acidosis. It also prevents the accumulation of toxic substances in the blood²¹. In a normal healthy individual, ketones act as a minor substrate to provide energy to the myocardium. During starvation, intake of diet rich in fats and the proteins, ketones get utilized in a proper manner. But during the deficiency of HMG- CoA lyase enzyme, the substrates that provide energy that is ketones get reduced leading to the dysfunction of myocardium. Beta oxidation of fatty acids produce ketones and 60-90% of the energy is provided to myocardium and the energy that is remaining is provided by glucose⁶. The utilization of mitochondrial enzyme regulates the uptake of fatty acids and prevents the accumulation at intracellular level. But the deficiency of HMG- CoA lyase enzyme impairs this regulatory process and leads to cytotoxicity of myochondria and dysfunctioning which leads to the accumulation of fatty acids at intracellular level²². In a normal healthy individual, carnitine plays an important role in the normal functioning of the myocardium.

Fatty acids get transported from the mitochondria into the cytosol for beta- oxidation by a process known as carnitin palmitoyltransferase shuttle system²⁴. Carnitine also has various other function such that it helps in scavenging the free radicals, helps in the metabolism of amino acids that are branched-chain, acts as a cofactor in the oxidation of fatty acids that are long-chain and also the process of nuclear transcription²³.But during the deficiency of HMG- CoA lyase enzyme, there is an occurrence of the deficiency of secondary carnitine due to the esterification of free carnitine to 3-methylglutarylcarnitine⁵.It has been reported that Levo-carnitine plays an important role in the dilatation process of left ventricle and the increase the rate of survival in patients suffering from dilated cardiomyopathy².

Screening of the newborn babies is crucial to test whether he or she is suffering from any disease as they can be deadly and lead to the death of the baby if left untreated. Some newborns also suffer from the diseases they don’t have any family history. Screening of the deficiency of HMG- CoA enzyme in the deficiency of newborn babies is done by using a technique known as tandem mass spectrometry²⁷.If the results show an increase in the level of C5-OH (3-hydroxyisovaleryl carnitine) it is possible that the newborn is suffering from the deficiency of HMG- CoA lyase enzyme^28.If the results appear to be positive doctor should immediately check the clinical condition of the newborn and consult with a doctor specialized in this field. A urine organic analysis or plasma acylcarnitine analysis on the newborn baby is performed to confirm the deficiency of HMG- CoA enzyme²⁶.

Screening of HMG-CoA Lyase Deficiency

Supportive care should be provided to such patients which is specialized care to get relieved from pain and stress, both physical and mental³⁰. It involves various doctors, nurses and other healthcare professionals to work in collaboration to help the patient in managing the disease and the treatment by the patients .The parents and other family members should be given a proper counseling and psychosocial care to the patients in order to improve emotional health and get rid of pain, anxiety, distress and low self esteem developed due to the disease⁸.Various other tests such as genetic testing that is the testing of DNA is also performed to check for the genes that cause the disease²⁹.

In Ontario, a heel- prick is used to collect the blood sample from the newborn babies and check for the deficiency of HMG- CoA lyase enzyme and various other diseases²¹. Testing of DNA is also performed in women who are pregnant to check for the presence of disease in the fetus by using Chorionic Villus Sampling which is a specialized test³⁰. It is mainly done during the 10^th and the 12^th week of pregnancy. A process called as amniocentesis is also performed to check for the deficiency of HMG- CoA lyase enzyme²³. It involves collection of fluid using a needle from the sac present around the fetus. This test is performed during the 13^th   and 20 ^th   week of pregnancy¹¹. Sometimes testing of the urine sample of the baby is also performed to check the level of acid and other toxic substances¹⁰. However, countries having a greater number of the disease, the newborn babies are also screened for various mutations such as such as c.122G>A, c.109G>T and c.504_505delCT in Spain, Saudi Arabia and Portugal⁴ The parents of the newborn patients should be counseled and provided psychosocial care to prevent depression and anxiety if their newborn baby suffers from the deficiency of HMG- CoA lyase enzyme.

The treatment method for the deficiency of HMG- CoA lyase enzyme lasts for a life time if detected²⁹. It is a difficult procedure to cure the disease in a complete manner. However, if the treatment is provided early and in a careful manner it can lead to normal growth and development of the newborn and cure the disease to a great extent but there is no permanent cure of the disease¹⁴. If there are no serious complications during the diagnosis of the disease, it takes  less time to get better in the newborns and  when they become adults, they are diagnosed with the absence of symptoms related to the disease. It requires proper guidance, management and monitoring of the disease for the well being of the newborn baby by the nurses, clinicians, dieticians, geneticists and other health care professionals³⁰.

Current and Future Treatment Options for HMG-CoA Lyase Deficiency

There are various treatment methods for the deficiency of HMG-CoA lyase such as nutritional therapy in which the patients are advised a diet having low leucine and high content of carbohydrates, calories and protein to achieve metabolic balance and develop proper growth and development²³. These patients are also advised the supplementation of L-Carnitine to remove the toxic substances from the body from the urine by the excretion process¹⁸. However, L-Carnitine plays an important role in the prevention of development of diseases related to the muscles of the heart²⁷. In the acute phase of the disease which depends on the symptoms of the patient, glucose is administered by intravenous means to control low sugar level in the blood and bicarbonate to prevent acidosis¹³. Maintenance therapy is also advised to new born patients to remove the toxic substances in the body by providing a balanced diet containing specific fat and proteins. It is recommended to prevent fasting during an acute phase of the disease and the main aim of nutritional therapy is to avoid excess catabolic activity, low blood sugar levels and metabolic acidosis¹⁸.

Monitoring of the amino acids present in plasma and growth of the infant is essential at regular intervals to make sure that the intake of leucine and proteins is adequate¹². The deficiency of leucine leads to low weight gain, irritation, loss of hair, loss of appetite and skin rashes¹⁰. If the intake of leucine is in excess it may accumulate organic acids to in the body leading to metabolic acidosis⁹. For younger children, a formula of routine infant is used to provide an adequate amount of leucine by giving milk which contains a natural protein¹⁰. The plasma samples should be taken after the meal is taken by the patients.The patient might suffer from the disease complications despite of adequate nutritional therapy if the newborn baby suffers from any kind of infection such as viral infection, ear infection or gastroenteritis². It becomes essential to maintain the homeostasis at biochemical level. There has been research going on various novel methods of treatment for this disease such as studying various components in urine by using NMR- spectroscopy technique and MRI of brain².

It can be concluded that HMG- CoA lyase deficiency is a rare inherited autosomal disorder¹. It involves the lack of processing an amino acid called as leucine present in the mitochondria which helps in the formation of proteins. In this disorder the body is also not able to make ketones in the liver which play an important role in providing energy by being used up in the body during fasting that is lack of food. This disease is screened during the birth of the child. During the deficiency of HMG- CoA lyase enzyme, the substrates that provide energy that is ketones get reduced leading to the dysfunction. Screening of the deficiency of HMG- CoA enzyme in the deficiency of newborn babies is done by using a technique known as tandem mass spectrometry.If the results show an increase in the level of C5-OH (3-hydroxyisovaleryl carnitine) it is possible that the newborn is suffering from the deficiency of HMG- CoA lyase enzyme. The treatment method for the deficiency of HMG- CoA lyase enzyme lasts for a life time if detected. Newborn babies suffering from deficiency of HMG- CoA enzyme require nutritional therapy and supportive care that is specialized care provided by the nurses, clinicians and other healthcare professionals. Various novel methods of treatment for this disease have been researched such as studying various components in urine by using spectroscopy technique and MRI of brain to check the abnormal peaks and diagnose the disease.

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