Depending on the affected gene(s), this disorder may present symptoms that range from mild to life-threatening.

- Stroke

- Progressive encephalopathy

- Seizure

- Kidney failure

- Vomiting

- Dehydration

- Failure to thrive and developmental delays

- Lethargy

- Repeated Yeast infections

- Acidosis

- Hepatomegaly

- Hypotonia

- Pancreatitis

- Respiratory distress

People with methylmalonyl CoA mutase deficiency exhibit many symptoms similar to other diseases involving inborn errors of metabolism. Sometimes the symptoms appear shortly after birth, but other times the onset of symptoms is later.

Newborn babies experience with vomiting, acidosis, hyperammonemia, hepatomegaly (enlarged livers), hyperglycinemia (high glycine levels), and hypoglycemia (low blood sugar). Later, cases of thrombocytopenia and neutropenia can occur.

In some cases intellectual and developmental disabilities, such as autism, were noted with increased frequency in populations with methylmalonyl-CoA mutase deficiency.

Methylmalonic acidemia (MMA), also called methylmalonic aciduria, is an autosomal recessive metabolic disorder. It is a classical type of organic acidemia. The result of this condition is the inability to properly digest specific fats and proteins, which in turn leads to a buildup of a toxic level of methylmalonic acid in the blood.

Methylmalonic acidemia stems from several genotypes, all forms of the disorder usually diagnosed in the early neonatal period, presenting progressive encephalopathy, and secondary hyperammonemia. The disorder can result in death if undiagnosed or left untreated. It is estimated that this disorder has a frequency of 1 in 48,000 births, though the high mortality rate in diagnosed cases make exact determination difficult. Methylmalonic acidemias are found with an equal frequency across ethnic boundaries.

Signs and symptoms of a biotinidase deficiency can appear several days after birth. These include seizures, hypotonia and muscle/limb weakness, ataxia, paresis, hearing loss, optic atrophy, skin rashes (including seborrheic dermatitis and psoriasis), and alopecia. If left untreated, the disorder can rapidly lead to coma and death.

Biotinidase deficiency can also appear later in life. This is referred to as "late-onset" biotinidase deficiency. The symptoms are similar, but perhaps more mild, because if an individual survives the neonatal period they likely have some residual activity of biotin-related enzymes. Studies have noted individuals who were asymptomatic until adolescence or early adulthood. One study pointed out that untreated individuals may not show symptoms until age 21. Furthermore, in rare cases, even individuals with profound deficiencies of biotinidase can be asymptomatic.

Symptom severity is predictably correlated with the severity of the enzyme defect. Profound biotinidase deficiency refers to situations where enzyme activity is 10% or less. Individuals with partial biotinidase deficiency may have enzyme activity of 10-30%.

Functionally, there is no significant difference between dietary biotin deficiency and genetic loss of biotin-related enzyme activity. In both cases, supplementation with biotin can often restore normal metabolic function and proper catabolism of leucine and isoleucine.

The symptoms of biotinidase deficiency (and dietary deficiency of biotin) can be quite severe. A 2004 case study from Metametrix detailed the effects of biotin deficiency, including aggression, cognitive delay, and reduced immune function.

Biotinidase deficiency is an autosomal recessive metabolic disorder in which biotin is not released from proteins in the diet during digestion or from normal protein turnover in the cell. This situation results in biotin deficiency.

Biotin, also called vitamin B, is an important water-soluble nutrient that aids in the metabolism of fats, carbohydrates, and proteins. Biotin deficiency can result in behavioral disorders, lack of coordination, learning disabilities and seizures. Biotin supplementation can alleviate and sometimes totally stop such symptoms.

This defect leads to a multi-systemic disorder of the connective tissue, muscles, central nervous system (CNS), and cardiovascular system. Homocystinuria represents a group of hereditary metabolic disorders characterized by an accumulation of the amino acid homocysteine in the serum and an increased excretion of homocysteine in the urine. Infants appear to be normal and early symptoms, if any are present, are vague.

Signs and symptoms of homocystinuria that may be seen include the following:

As with several other metabolic conditions, OTC deficiency can have variable presentations, regarding age of onset and the severity of symptoms. This compounded when considering heterozygous females and the possibility of non-random X-inactivation. In the classic and most well-known presentation, a male infant appears well initially, but by the second day of life they are irritable, lethargic and stop feeding. A metabolic encephalopathy develops, and this can progress to coma and death without treatment. Ammonia is only toxic to the brain, other tissues can handle elevated ammonia concentrations without problems.

Later onset forms of OTC deficiency can have variable presentations. Although late onset forms of the disease are often considered milder than the classic infantile presentation, any affected individual is at risk for an episode of hyperammonemia that could still be life-threatening, if presented with the appropriate stressors. These patients will often present with headaches, nausea, vomiting, delayed growth and a variety of psychiatric symptoms (confusion, delirium, aggression, or self-injury). A detailed dietary history of an affected individual with undiagnosed OTC deficiency will often reveal a history of protein avoidance.

The prognosis of a patient with severe OTC deficiency is well correlated with the length of the hyperammonemic period rather than the degree of hyperammonemia or the presence of other symptoms, such as seizures. Even for patients with late onset forms of the disease, their overall clinical picture is dependent on the extent of hyperammonemia they have experienced, even if it has remained unrecognized.

The term fatty acid oxidation disorder (FAOD) is sometimes used, especially when there is an emphasis on the oxidation of the fatty acid.

In addition to the fetal complications, they can also cause complications for the mother during pregnancy.

Examples include:

- trifunctional protein deficiency

- MCADD, LCHADD, and VLCADD

Carbamoyl phosphate synthetase I deficiency often becomes evident in the first few days of life. An infant with this condition may be lacking in energy (lethargic) or unwilling to eat, and have a poorly controlled breathing rate or body temperature. Some babies with this disorder may experience seizures or unusual body movements, or go into a coma. Complications of carbamoyl phosphate synthetase I deficiency may include developmental delay and mental retardation.

In some affected individuals, signs and symptoms of carbamoyl phosphate synthetase I deficiency may be less severe, and may not appear until later in life.

The presentation of mitochondrial trifunctional protein deficiency may begin during infancy, features that occur are: low blood sugar, weak muscle tone, and liver problems. Infants with this disorder are at risk for heart problems, breathing difficulties, and pigmentary retinopathy. Signs and symptoms of mitochondrial trifunctional protein deficiency that may begin "after" infancy include hypotonia, muscle pain, a breakdown of muscle tissue, and a loss of sensation in the extremities called peripheral neuropathy. Some who have MTP deficiency show a progressive course associated with myopathy, and recurrent rhabdomyolysis.

Classical homocystinuria, also known as cystathionine beta synthase deficiency or CBS deficiency, is an inherited disorder of the metabolism of the amino acid methionine, often involving cystathionine beta synthase. It is an inherited autosomal recessive trait, which means a child needs to inherit a copy of the defective gene from both parents to be affected.

The signs and symptoms of this disorder typically appear in early childhood. Almost all affected children have delayed development. Additional signs and symptoms can include weak muscle tone (hypotonia), seizures, diarrhea, vomiting, and low blood sugar (hypoglycemia). A heart condition called cardiomyopathy, which weakens and enlarges the heart muscle, is another common feature of malonyl-CoA decarboxylase deficiency.

Some common symptoms in Malonyl-CoA decarboxylase deficiency, such as cardiomyopathy and metabolic acidosis, are triggered by the high concentrations of Malonyl-CoA in the cytoplasm. High level of Malonyl-CoA will inhibits β-oxidation of fatty acids through deactivating the carrier of fatty acyl group, CPT1, and thus, blocking fatty acids from going into the mitochondrial matrix for oxidation.

A research conducted in Netherlands has suggested that carnitine supplements and a low fat diet may help to reduce the level of malonic acid in our body.

Methylmalonyl-CoA mutase is a mitochondrial homodimer apoenzyme (EC. 5. 4.99.2) that focuses on the catalysis of methylmalonyl CoA to succinyl CoA. The enzyme is bound to adenosylcobalamin, a hormonal derivative of vitamin B12 in order to function. Methylmalonyl-CoA mutase deficiency is caused by genetic defect in the MUT gene responsible for encoding the enzyme. Deficiency in this enzyme accounts for 60% of the cases of methylmalonic acidemia.

Short-chain acyl-coenzyme A dehydrogenase deficiency affected infants will have vomiting, low blood sugar, a lack of energy (lethargy), poor feeding, and failure to gain weight and grow. Additional features of this disorder may include poor muscle tone (hypotonia), seizures, developmental delays, and microcephaly. The symptoms of short-chain acyl-CoA dehydrogenase deficiency may be triggered during illnesses such as viral infections. In some cases, signs and symptoms may not appear until adulthood, when some individuals may develop muscle weakness, while other individuals mild symptoms may never be diagnosed.

Signs and symptoms of CTLN1 in infants are caused by increasing levels of ammonia in the blood and cerebrospinal fluid and include excessive vomiting, anorexia, refusal to eat, irritability, increased intracranial pressure, and worsening lethargy, seizures, hypotonia, respiratory distress, hepatomegaly, and cerebral edema. These symptoms appear within days of birth in the more severe forms of the disease with complete deficiency of the enzyme. As ammonia accumulates further, the affected infant may enter a hyperammonemic coma, which indicates neurological damage and can cause developmental delays, cognitive disabilities, cerebral palsy, hypertonia, spasticity, ankle clonus, seizures, and liver failure.

Milder forms of the disease are caused by partial arginosuccinate synthetase deficiency and may manifest in childhood or in adulthood. Symptoms of mild CTLN1 include failure to thrive, avoidance of high-protein foods, ataxia, worsening lethargy, and vomiting. Hyperammonemic coma can still develop in these people. CTLN1 can also develop in the perinatal period.

Tetrahydrobiopterin deficiency (THBD, BHD), also called THB or BH deficiency, is a rare metabolic disorder that increases the blood levels of phenylalanine. Phenylalanine is an amino acid obtained through the diet. It is found in all proteins and in some artificial sweeteners. If tetrahydrobiopterin deficiency is not treated, excess phenylalanine can build up to harmful levels in the body, causing intellectual disability and other serious health problems.

High levels of phenylalanine are present from infancy in people with untreated tetrahydrobiopterin (THB, BH) deficiency. The resulting signs and symptoms range from mild to severe. Mild complications may include temporary low muscle tone. Severe complications include intellectual disability, movement disorders, difficulty swallowing, seizures, behavioral problems, progressive problems with development, and an inability to control body temperature.

It was first characterized in 1975.

A broad classification for genetic disorders that result from an inability of the body to produce or utilize one enzyme that is required to oxidize fatty acids. The enzyme can be missing or improperly constructed, resulting in it not working. This leaves the body unable to produce energy within the liver and muscles from fatty acid sources.

The body's primary source of energy is glucose; however, when all the glucose in the body has been expended, a normal body digests fats. Individuals with a fatty-acid metabolism disorder are unable to metabolize this fat source for energy, halting bodily processes. Most individuals with a fatty-acid metabolism disorder are able to live a normal active life with simple adjustments to diet and medications.

If left undiagnosed many complications can arise. When in need of glucose the body of a person with a fatty-acid metabolism disorder will still send fats to the liver. The fats are broken down to fatty acids. The fatty acids are then transported to the target cells but are unable to be broken down, resulting in a build-up of fatty acids in the liver and other internal organs.

Fatty-acid metabolism disorders are sometimes classified with the lipid metabolism disorders, but in other contexts they are considered a distinct category.

Ornithine transcarbamylase deficiency also known as OTC deficiency is the most common urea cycle disorder in humans. Ornithine transcarbamylase, the defective enzyme in this disorder is the final enzyme in the proximal portion of the urea cycle, responsible for converting carbamoyl phosphate and ornithine into citrulline. OTC deficiency is inherited in an X-linked recessive manner, meaning males are more commonly affected than females.

In severely affected individuals, ammonia concentrations increase rapidly causing ataxia, lethargy and death without rapid intervention. OTC deficiency is diagnosed using a combination of clinical findings and biochemical testing, while confirmation is often done using molecular genetics techniques.

Once an individual has been diagnosed, the treatment goal is to avoid precipitating episodes that can cause an increased ammonia concentration. The most common treatment combines a low protein diet with nitrogen scavenging agents. Liver transplant is considered curative for this disease. Experimental trials of gene therapy using adenoviral vectors resulted in the death of one participant, Jesse Gelsinger, and have been discontinued.

Symptoms of congenital Type III Galactosemia are apparent from birth, but vary in severity depending on whether the peripheral or generalized disease form is present. Symptoms may include:

- Infantile jaundice

- Infantile hypotonia

- Dysmorphic features

- Sensorineural hearing loss

- Impaired growth

- Cognitive deficiencies

- Depletion of cerebellar Purkinje cells

- Ovarian failure (POI) and hypertrophic hypergonadism

- Liver failure

- Renal failure

- Splenomegaly

- Cataracts

Studies of Type III galactosemia symptoms are mostly descriptive, and precise pathogenic mechanisms remain unknown. This is largely due to a lack of functional animal models of classic galactosemia. The recent development of a "Drosophila melanogaster" GALE mutant exhibiting galactosemic symptoms may yield a promising future animal model.

Malonyl-CoA decarboxylase deficiency (MCD), or Malonic aciduria is an autosomal-recessive metabolic disorder caused by a genetic mutation that disrupts the activity of Malonyl-Coa decarboxylase. This enzyme breaks down Malonyl-CoA (a fatty acid precursor and a fatty acid oxidation blocker) into Acetyl-CoA and carbon dioxide.

Phosphofructokinase deficiency also presents in a rare infantile form. Infants with this deficiency often display floppy infant syndrome (hypotonia), arthrogryposis, encephalopathy and cardiomyopathy. The disorder can also manifest itself in the central nervous system, usually in the form of seizures. PFK deficient infants also often have some type of respiratory issue. Survival rate for the infantile form of PFK deficiency is low, and the cause of death is often due to respiratory failure.

Some patients suffering from copper deficiency have shown signs of vision and color loss. The vision is usually lost in the peripheral views of the eye. The bilateral vision loss is usually very gradual. An optical coherence tomography (OCT) shows some nerve fiber layer loss in most patients, suggesting the vision loss and color vision loss was secondary to optic neuropathy or neurodegeneration.

Another common symptom of copper deficiency is peripheral neuropathy, which is numbness or tingling that can start in the extremities and can sometimes progress radially inward towards the torso. In an Advances in Clinical Neuroscience & Rehabilitation (ACNR) published case report, a 69-year-old patient had progressively worsened neurological symptoms. These symptoms included diminished upper limb reflexes with abnormal lower limb reflexes, sensation to light touch and pin prick was diminished above the waist, vibration sensation was lost in the sternum, and markedly reduced proprioception or sensation about the self’s orientation. Many people suffering from the neurological effects of copper deficiency complain about very similar or identical symptoms as the patient. This numbness and tingling poses danger for the elderly because it increases their risk of falling and injuring themselves. Peripheral neuropathy can become very disabling leaving some patients dependent on wheel chairs or walking canes for mobility if there is lack of correct diagnosis. Rarely can copper deficiency cause major disabling symptoms. The deficiency will have to be present for an extensive amount of time until such disabling conditions manifest.

Late-onset PFK deficiency, as the name suggests, is a form of the disease that presents later in life. Common symptoms associated with late-onset phosphofructokinase deficiency are myopathy, weakness and fatigue. Many of the more severe symptoms found in the classic type of this disease are absent in the late-onset form.

Mitochondrial trifunctional protein deficiency is an autosomal recessive fatty acid oxidation disorder that prevents the body from converting certain fats to energy, particularly during periods without food. People with this disorder have inadequate levels of an enzyme that breaks down a certain group of fats called long-chain fatty acids.