In terms of the diagnosis of adenylosuccinate lyase deficiency one should look for (or exam/method):

- MRI

- Demonstration of Succinylpurines in extracellular fluids like plasma, cerebrospinal fluid (CSF) and/or urine using HPLC or HPLC-MS

- Genetic testing - genomic cDNA sequencing of the ADSL gene and characterization of mutant proteins.

While the disease manifests early in life in most cases, diagnosis of the disease is often quite delayed. The symptoms that affected patients present vary, but the most common presenting symptoms are gastrointestinal issues such as nausea, vomiting, abdominal pain, and diarrhea, and neurologic or ocular symptoms such as hearing loss, weakness, and peripheral neuropathy. These gastrointestinal symptoms cause patients with MNGIE to be very thin and experience persistent weight loss and this often leads to MNGIE being misdiagnosed as an eating disorder. These symptoms without presentation of disordered eating and warped body image warrant further investigation into the possibility of MNGIE as a diagnosis. Presentation of these symptoms and lack of disordered eating are not enough for a diagnosis. Radiologic studies showing hypoperistalsis, large atonic stomach, dilated duodenum, diverticula, and white matter changes are required to confirm the diagnosis. Elevated blood and urine nucleoside levels are also indicative of MNGIE syndrome. Abnormal nerve conduction as well as analysis of mitochondria from liver, intestines, muscle, and nerve tissue can also be used to support the diagnosis.

A successful treatment for MNGIE has yet to be found, however, symptomatic relief can be achieved using pharmacotherapy and celiac plexus neurolysis. Celiac plexus neurolysis involves interrupting neural transmission from various parts of the gastrointestinal tract. By blocking neural transmission, pain is relieved and gastrointestinal motility increases. Stem cell therapies are currently being investigated as a potential cure for certain patients with the disease, however, their success depends on physicians catching the disease early before too much organ damage has occurred.

The prognosis of this condition in childhood usually has a stable outcome, whereas in neonatal is almost always fatal, according to Jurecka, et al.

There is a diagnostic test for AIE that looks for an antibody against the enterocyte. The diagnostic test contains the Western Blot which can identify the antibody IgG or IgA and with the immunohistochemistry can localize these antibodies. Endoscopy with biopsies of the colon, small colon, stomach, and other locations may be helpful in diagnosing. This test is done to look at the stomach and small intestines and to see what cells are infiltrating the digestive tract. There are also documented cases of autoimmune enteropathy where the auto-antibodies were undetectable and the diagnosis was made on the basis of clinical presentation and response to treatment.

HFM must be distinguished from cerebral folate deficiency (CFD)– a condition in which there is normal intestinal folate absorption, without systemic folate deficiency, but a decrease in CSF folate levels. This can accompany a variety of disorders. One form of CFD is due to loss-of-mutations in folate receptor-α, (FRα), which transports folates via an endocytic process. While PCFT is expressed primarily at the basolateral membrane of the choroid plexus, FRα, is expressed primarily at the apical brush-border membrane. Unlike subjects with HFM, patients with CFD present with neurological signs a few years after birth. The basis for the delay in the appearance of clinical manifestations due to loss of FRα function is not clear; the normal blood folate levels may be protective, although for a limited time.

As of June 2014 (the latest update on HFM in GeneReviews) a total of 32 families had been reported with a clinical diagnosis of HFM of which there was genotypic confirmation in 24 families. Since then, another two confirmed cases have been reported and an additional case was reported based on a clinical diagnosis alone. Most cases emerge from consanguineous parents with homozygous mutations. There are three instances of HFM from non-consanguineous parents in which there were heterozygous mutations. HFM cases are worldwide with mostly private mutations. However, a number of families of Puerto Rican ancestry have been reported with a common pathogenic variant at a splice receptor site resulting in the deletion of exon 3 and the absence of transport function. A subsequent population-based study of newborn infants in Puerto Rico identified the presence of the same variant on the island. Most of the pathogenic variants result in a complete loss of the PCFT protein or point mutations that result in the complete loss of function. However, residual function can be detected with some of the point mutants.

Infant mortality is high for patients diagnosed with early onset; mortality can occur within less than 2 months, while children diagnosed with late-onset syndrome seem to have higher rates of survival. Patients suffering from a complete lesion of mut0 have not only the poorest outcome of those suffering from methylaonyl-CoA mutase deficiency, but also of all individuals suffering from any form of methylmalonic acidemia.

Familial LPL deficiency should be considered in anyone with severe hypertriglyceridemia and the chylomicronemia syndrome. The absence of secondary causes of severe hypertriglyceridemia (like e.g. diabetes, alcohol, estrogen-, glucocorticoid-, antidepressant- or isotretinoin-therapy, certain antihypertensive agents, and paraproteinemic disorders) increases the possibility of LPL deficiency. In this instance besides LPL also other loss-of-function mutations in genes that regulate catabolism of triglyceride-rich lipoproteins (like e.g. ApoC2, ApoA5, LMF-1, GPIHBP-1 and GPD1) should also be considered

The diagnosis of familial lipoprotein lipase deficiency is finally confirmed by detection of either homozygous or compound heterozygous pathogenic gene variants in "LPL" with either low or absent lipoprotein lipase enzyme activity.

Lipid measurements

· Milky, lipemic plasma revealing severe hyperchylomicronemia;

· Severely elevated fasting plasma triglycerides (>2000 mg/dL);

LPL enzyme

· Low or absent LPL activity in post-heparin plasma;

· LPL mass level reduced or absent in post-heparin plasma;

Molecular genetic testing

The LPL gene is located on the short (p) arm of chromosome 8 at position 22. More than 220 mutations in the LPL gene have been found to cause familial lipoprotein lipase deficiency so far.

Microscopic analysis of the hair shows twisted hairs of unequal size and different shapes (pili torti, aniso- and poikilotrichosis), longitudinal breaks and breaks located at nodes (trichorrhexis nodosa). Scanning electron microscopy might reveal hair budding (trichorrhexis blastysis). Biochemical analysis may reveal sulfur-deficient brittle hair (trichothiodystrophy; note that disulfide bonds determine hair waviness).

Immunodeficiency is a consistent feature with low serum concentrations of immunoglobulins which may improve with age and a poor immunological response to childhood vaccination. T cell dysfunction and abnormal antibody generation have been reported.

In the absence of a liver transplant, FAP is invariably fatal, usually within a decade. The disadvantage of liver transplantation is that approximately 10% of the subjects die from the procedure or complications resulting from the procedure, which is a form of gene therapy wherein the liver expressing wild type and mutant TTR is replaced by a liver only expressing wild type TTR. Moreover, transplanted patients must take immune suppressants (drugs) for the remainder of their life, which can lead to additional complications. In late 2011, the European Medicines Agency approved the transthyretin kinetic stabilizer Tafamidis or Vyndaqel discovered by Jeffery W. Kelly and developed by FoldRx pharmaceuticals (acquired by Pfizer in 2010) for the treatment of FAP based on clinical trial data. Tafamidis (20 mg once daily) slowed the progression of FAP over a 36-month period and importantly reversed the weight loss and muscle wasting associated with disease progression.

There are multiple large-field, multi-country research initiatives focusing on strategies to prevent and treat EE.

- The MAL-ED project

- The Alive and Thrive nutrition project

- The Sanitation, Hygiene and Infant Nutrition Efficacy (SHINE) Trial (ClinicalTrials.gov identifier: NCT01824940)

- The WASH Benefits Study

A physical examination may reveal a mass or distention of the abdomen.

Tests which may be useful for diagnosis include:

- Abdominal x-ray

- Abdominal CT scan

- Contrast enema study

In terms of diagnosis for this condition, the following methods/tests are available:

- Endoscopic

- CT scan

- Serum endocrine autoantibody screen

- Histologic test

The current gold standard diagnostic test for EE is intestinal biopsy and histological analysis. Histological changes observed include:

- Villous blunting

- Crypt hypertrophy

- Villous fusion

- Mucosal inflammation

However, this procedure is considered too invasive, complex and expensive to be implemented as standard of care. As a result, there are various research efforts underway to identify biomarkers associated with EE, which could serve as less invasive, yet representative, tools to screen for and identify EE from stool samples.

In an effort to identify simple, accurate diagnostic tests for EE, the Bill and Melinda Gates Foundation (BMGF) has established an EE biomarkers consortium as part of their Global Grand Challenges initiative (specifically, the Discover Biomarkers of Gut Function challenge).

So far, various biomarkers have been selected and studied based on the current understanding of EE pathophysiology:

- Gut permeability/barrier function

- Dual sugar permeability (lactose-to-mannitol ratio)

- Intestinal inflammation

- Alpha-1 anti-trypsin

- Neopterin

- Myeloperoxidase

- Exocrine (hormonal) markers

- Bacterial translocation markers

- Endotoxin core antibody

- Markers of systemic inflammation

- Alpha-1 glycoprotein

- C-reactive protein (CRP)

It is postulated that the limited of understanding of EE is partially due to the paucity of reliable biomarkers, making it difficult for researchers to track the epidemiology of the condition and assess the efficacy of interventions.

The term homocystinuria describes an increased excretion of the thiol amino acid homocysteine in urine (and incidentally, also an increased concentration in plasma). The source of this increase may be one of many metabolic factors, only one of which is CBS deficiency. Others include the re-methylation defects (cobalamin defects, methionine sythase deficiency, MTHFR) and vitamin deficiencies (cobalamin (vitamin B12) deficiency, folate (vitamin B9) deficiency, riboflavin deficiency (vitamin B2), pyridoxal phosphate deficiency (vitamin B6)). In light of this information, a combined approach to laboratory diagnosis is required to reach a differential diagnosis.

CBS deficiency may be diagnosed by routine metabolic biochemistry. In the first instance, plasma or urine amino acid analysis will frequently show an elevation of methionine and the presence of homocysteine. Many neonatal screening programs include methionine as a metabolite. The disorder may be distinguished from the re-methylation defects (e.g., MTHFR, methionine synthase deficiency and the cobalamin defects) in lieu of the elevated methionine concentration. Additionally, organic acid analysis or quantitative determination of methylmalonic acid should help to exclude cobalamin (vitamin B12) defects and vitamin B12 deficiency giving a differential diagnosis.

The laboratory analysis of homocysteine itself is complicated because most homocysteine (possibly above 85%) is bound to other thiol amino acids and proteins in the form of disulphides (e.g., cysteine in cystine-homocysteine, homocysteine in homocysteine-homocysteine) via disulfide bonds. Since as an equilibrium process the proportion of free homocystene is variable a true value of total homocysteine (free + bound) is useful for confirming diagnosis and particularly for monitoring of treatment efficacy. To this end it is prudent to perform total homocyst(e)ine analysis in which all disulphide bonds are subject to reduction prior to analysis, traditionally by HPLC after derivatisation with a fluorescent agent, thus giving a true reflection of the quantity of homocysteine in a plasma sample.

The drug tafamidis has completed a phase II/III 18-month-long placebo controlled clinical trial

and these results in combination with an 18-month follow-on study demonstrated that Tafamidis or Vyndaqel slowed progression of FAP, particularly when administered to patients early in the course of FAP. This drug is now approved by the European Medicines Agency.

The US Food and Drug Administration's Peripheral and Central Nervous System Drugs Advisory Committee rejected the drug in June 2012, in a 13-4 vote. The committee stated that there was not enough evidence supporting efficacy of the drug, and requested additional clinical trials.

Whether MTHFR deficiency has any effect at all on all-cause mortality is unclear. One Dutch study showed that the MTHFR mutation was more prevalent in younger individuals (36% relative to 30%), and found that elderly men with MTHFR had an elevated mortality rate, attributable to cancer. Among women, however, no difference in life expectancy was seen. More recently, however, a meta-analysis has shown that overall cancer rates are barely increased with an odds ratio of 1.07, which suggests that an impact on mortality from cancer is small or zero.

People with hypermethioninemia often do not show any symptoms. Some individuals with hypermethioninemia exhibit learning disabilities, mental retardation, and other neurological problems; delays in motor skills such as standing or walking; sluggishness; muscle weakness; liver problems; unusual facial features; and their breath, sweat, or urine may have a smell resembling boiled cabbage.

Hypermethioninemia can occur with other metabolic disorders, such as homocystinuria, tyrosinemia and galactosemia, which also involve the faulty breakdown of particular molecules. It can also result from liver disease or excessive dietary intake of methionine from consuming large amounts of protein or a methionine-enriched infant formula.

Since the essential pathology is due to the inability to absorb vitamin B from the bowels, the solution is therefore injection of IV vitamin B. Timing is essential, as some of the side effects of vitamin B deficiency are reversible (such as RBC indices, peripheral RBC smear findings such as hypersegmented neutrophils, or even high levels of methylmalonyl CoA), but some side effects are irreversible as they are of a neurological source (such as tabes dorsalis, and peripheral neuropathy). High suspicion should be exercised when a neonate, or a pediatric patient presents with anemia, proteinuria, sufficient vitamin B dietary intake, and no signs of pernicious anemia.

Several tests can be done to discover the dysfunction of methylmalonyl-CoA mutase. Ammonia test, blood count, CT scan, MRI scan, electrolyte levels, genetic testing, methylmalonic acid blood test, and blood plasma amino acid tests all can be conducted to determine deficiency.

There is no treatment for complete lesion of the mut0 gene, though several treatments can help those with slight genetic dysfunction. Liver and kidney transplants, and a low-protein diet all help regulate the effects of the diseases.

There is no single, specific test for malabsorption. As for most medical conditions, investigation is guided by symptoms and signs. A range of different conditions can produce malabsorption and it is necessary to look for each of these specifically. Many tests have been advocated, and some, such as tests for pancreatic function are complex, vary between centers and have not been widely adopted. However, better tests have become available with greater ease of use, better sensitivity and specificity for the causative conditions. Tests are also needed to detect the systemic effects of deficiency of the malabsorbed nutrients (such as anaemia with vitamin B12 malabsorption).

Bile acid malabsorption is common in Crohn's disease but not always recognised. Most patients with previous ileal resection and chronic diarrhea will have abnormal SeHCAT tests and can benefit from bile acid sequestrants.

Patients with primary bile acid diarrhea are frequently misdiagnosed as having the irritable bowel syndrome as clinicians fail to recognize the condition. When SeHCAT testing is performed, the diagnosis of primary bile acid diarrhea is commonly made. In a review of 18 studies of the use of SeHCAT testing in diarrhea-predominant irritable bowel syndrome patients, 32% of 1223 patients had a SeHCAT 7-day retention of less than 10%, and 80% of these reported a response to cholestyramine, a bile acid sequestrant.

Estimates of the population prevalence taken from this review suggest that 1% of the adult population could have primary bile acid diarrhea (Type 2 bile acid malabsorption).

One of, if not the most common form of organic acidemia, methylmalonic acidemia is not apparent at birth as symptoms usually do not present themselves until proteins are added to the infant's diet. Because of this, symptoms typically manifest anytime within the first year of life. Due to the severity and rapidity in which this disorder can cause complications when left undiagnosed, screening for methylmalonic acidemia is often included in the newborn screening exam.

Because of the inability to properly break down amino acids completely, the byproduct of protein digestion, the compound methylmalonic acid, is found in a disproportionate concentration in the blood and urine of those afflicted. These abnormal levels are used as the main diagnostic criteria for diagnosing the disorder. This disorder is typically determined through the use of a urine analysis or blood panel. The presence of methylmalonic acidemia can also be suspected through the use of a CT or MRI scan or ammonia test, however these tests are by no means specific and require clinical and metabolic/correlation. Elevated levels of ammonia, glycine, and ketone bodies may also be present in the blood and urine.

Sucrose intolerance can be caused by genetic mutations in which both parents must contain this gene for the child to carry the disease (so-called primary sucrose intolerance). Sucrose intolerance can also be caused by irritable bowel syndrome, aging, or small intestine disease (secondary sucrose intolerance). There are specific tests used to help determine if a person has sucrose intolerance. The most accurate test is the enzyme activity determination, which is done by biopsying the small intestine. This test is a diagnostic for GSID. Other tests which can aid in the diagnosis of GSID but which are not truly diagnostic for the disease are the sucrose breath test, and a genetic test which tests for the absence of certain genes which are thought to be responsible for GSID.

Sucrose (also termed "saccharose") is a disaccharide and is a two-sugar chain composed of glucose and fructose which are bonded together. A more familiar name is table, beet, or cane sugar. It was believed that most cases of sucrose intolerance were to do an autosomal recessive, genetic, metabolic disease. Based on new data patients with heterozygous and compound heterozygous genotypes can have symptom presentation as well. GSID involves deficiency in the enzyme sucrase-isomaltase, which breaks apart the glucose and fructose molecules. When disaccharides are consumed, they must be broken down into monosaccharides by enzymes in the intestines before they can be absorbed. Monosaccharides, or single sugar units, are absorbed directly into the blood.

A deficiency of sucrase may result in malabsorption of sugar, which can lead to potentially serious symptoms. Since sucrose-isomaltase is involved in the digestion of starches, some GSID patients may not be able to absorb starches as well. It is important for those with sucrose intolerance to minimize sucrose consumption as much as possible. Dietary supplements or medications may be taken as a substitute for the enzyme missing or to introduce healthy bacteria into the immune system.