Elevated levels of serum cholestanol are diagnostic of CTX. Alternatively analysis of 27-hydroxycholesterol and 7 alpha hydroxycholesterol can be used. Genetic testing of the CYP27A1 gene is confirmatory and is increasingly being used as a first line test as part of symptom specific gene panels (genetic eye disease, ataxia, dementia).

The most characteristic biochemical indicator of SLOS is an increased concentration of 7DHC (reduced cholesterol levels are also typical, but appear in other disorders as well). Thus, prenatally, SLOS is diagnosed upon finding an elevated 7DHC:total sterol ratio in fetal tissues, or increased levels of 7DHC in amniotic fluid. The 7DHC:total sterol ratio can be measured at 11–12 weeks of gestation by chorionic villus sampling, and elevated 7DHC in amniotic fluid can be measured by 13 weeks. Furthermore, if parental mutations are known, DNA testing of amniotic fluid or chorionic villus samples may be performed.

Amniocentesis (process of sampling amniotic fluid) and chorionic villus sampling cannot be performed until approximately 3 months into the pregnancy. Given that SLOS is a very severe syndrome, parents may want to choose to terminate their pregnancy if their fetus is affected. Amniocentesis and chorionic villus sampling leave very little time to make this decision (abortions become more difficult as the pregnancy advances), and can also pose severe risks to the mother and baby. Thus, there is a very large desire for noninvasive midgestation diagnostic tests. Examining the concentrations of sterols in maternal urine is one potential way to identify SLOS prenatally. During pregnancy, the fetus is solely responsible for synthesizing the cholesterol needed to produce estriol. A fetus with SLOS cannot produce cholesterol, and may use 7DHC or 8DHC as precursors for estriol instead. This creates 7- or 8-dehydrosteroids (such as 7-dehydroestriol), which may show up in the maternal urine. These are novel metabolites due to the presence of a normally reduced double bond at carbon 7 (caused by the inactivity of DHCR7), and may be used as indicators of SLOS. Other cholesterol derivatives which possess a double bond at the 7th or 8th position and are present in maternal urine may also be indicators of SLOS. 7- and 8-dehydropregnanetriols have been shown to be present in the urine of mothers with an affected fetus but not with an unaffected fetus, and thus are used in diagnosis. These pregnadienes originated in the fetus and traveled through the placenta before reaching the mother. Their excretion indicates that neither the placenta nor the maternal organs have necessary enzymes needed to reduce the double bond of these novel metabolites.

If SLOS goes undetected until after birth, diagnosis may be based on the characteristic physical features as well as finding increased plasma levels of 7DHC.

There are many different ways of detecting 7DHC levels in blood plasma, one way is using the Liebermann–Burchard (LB) reagent. This is a simple colorimetric assay developed with the intention of use for large scale screening. When treated with the LB reagent, SLOS samples turn pink immediately and gradually become blue; normal blood samples are initially colorless and develop a faint blue color. Although this method has limitations and is not used to give a definitive diagnosis, it has appeal in that it is a much faster method than using cell cultures.

Another way of detecting 7DHC is through gas chromatography, a technique used to separate and analyze compounds. Selected ion

monitoring gas chromatography/mass-spectrometry (SIM-GC/MS) is a very sensitive version of gas chromatography, and permits detection of even mild cases of SLOS. Other methods include time-of-flight mass spectrometry, particle-beam LC/MS, electrospray tandem MS, and ultraviolet absorbance, all of which may be used on either blood samples, amniotic fluid, or chorionic villus. Measuring levels of bile acids in patients urine, or studying DCHR7 activity in tissue culture are also common postnatal diagnostic techniques.

It is one of the 29 conditions currently recommended for newborn screening by the American College of Medical Genetics.

MDDS is diagnosed based on systemic symptoms presenting in infants, followed by a clinical examination and laboratory tests (for example, high lactate levels are common) medical imaging, and usually is finally confirmed and formally identified by genetic testing.

Most individuals with SBCADD are identified through newborn screening, where they present with an elevation of a five carbon acylcarnitine species. Confirmatory testing includes plasma and urine analysis to identify the carnitine and glycine conjugates of 2-methylbutyryl-CoA.

Human findings provide insufficient data for developing treatments due to differences in the patients physiological and metabolic disorders thus, a suitable alternative animal model is essential in obtaining a better understanding of the SR deficiency. In this particular case, researchers used silkworms to identify and characterize mutations relating to SPR activity from an initial purified state created in the larvae of the silkworm. The researchers used genetic and biochemical approaches to demonstrate oral administration of BH and dopamine which increased the survival rates of the silkworm larvae. The results indicate that BH deficiency in silkworms leads to death in response to the lack of dopamine. This shows that silkworms can be useful insect models in additional SR deficiency research and study.

The diagnosis of short-chain acyl-coenzyme A dehydrogenase deficiency is based on the following:

- Newborn screening test

- Genetic testing

- Urine test

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.

The diagnosis of SR deficiency is based on the analysis of the pterins and biogenic amines found in the cerebrospinal fluid (CSF) of the brain. The pterin compound functions as a cofactor in enzyme catalysis and biogenic amines which include adrenaline, dopamine, and serotonin have functions that vary from the control of homeostasis to the management of cognitive tasks. This analysis reveals decreased concentrations of homovanillic acid (HVA), 5-hydroxyindolacetic acid (HIAA), and elevated levels of 7,8-dihydrobiopterin, a compound produced in the synthesis of neurotransmitters. Sepiapterin is not detected by the regularly used methods applied in the investigation of biogenic monoamines metabolites in the cerebrospinal fluid. It must be determined by specialized methods that work by indicating a marked and abnormal increase of sepiapterin in cerebrospinal fluid. Confirmation of the diagnosis occurs by demonstrating high levels of CSF sepiapterin and a marked decrease of SR activity of the fibroblasts along with SPR gene molecular analysis.

The standard treatment is chenodeoxycholic acid (CDCA) replacement therapy. Serum cholesterol levels are also followed. If hypercholesterolemia is not controlled with CDCA, an HMG-CoA reductase inhibitor ("statins" such as simvastatin) can also be used.

A 2006 study of 279 patients found that of those with symptoms (185, 66%), 95% had suffered an encephalopathic crises usually with following brain damage. Of the persons in the study, 49 children died and the median age of death was 6.6 years. A Kaplan-Meier analysis of the data estimated that about 50% of symptomatic cases would die by the age of 25.

Diagnosis of mitochondrial trifunctional protein deficiency is often confirmed using tandem mass spectrometry. It should be noted that genetic counseling is available for this condition. Additionally the following exams are available:

- CBC

- Urine test

The differential diagnosis for short-chain acyl-coenzyme A dehydrogenase deficiency is: ethylmalonic encephalopathy, mitochondrial respiratory chain defects and "multiple" acyl-CoA dehydrogenase deficiency.

The diagnosis is based on clinical features, with a concomitant decreased blood adenosine deaminase level supporting the diagnosis.

Stress caused by infection, fever or other demands on the body may lead to worsening of the signs and symptoms, with only partial recovery.

Clinically, MCADD or another fatty acid oxidation disorder is suspected in individuals who present with lethargy, seizures, coma and hypoketotic hypoglycemia, particularly if triggered by a minor illness. MCADD can also present with acute liver disease and hepatomegaly, which can lead to a misdiagnosis of Reye syndrome. In some individuals, the only manifestation of MCADD is sudden, unexplained death often preceded by a minor illness that would not usually be fatal.

In areas with expanded newborn screening using tandem mass spectrometry (MS/MS), MCADD is usually detected shortly after birth, by the analysis of blood spots collected on filter paper. Acylcarnitine profiles with MS/MS will show a very characteristic pattern of elevated hexanoylcarnitine (C6), octanoylcarnitine (C8), decanoylcarnitine (C10) or decenoylcarnitine (C10:1), with C8 being greater than C6 and C10. Secondary carnitine deficiency is sometimes seen with MCADD, and in these cases, acylcarnitine profiles may not be informative. Urine organic acid analysis by gas chromatography-mass spectrometry (GC-MS) will show a pattern of dicarboxylic aciduria with low levels of ketones. Traces of acylglycine species may also be detected. Asymptomatic individuals may have normal biochemical lab results. For these individuals, targeted analysis of acylglycine species by GC-MS, specifically hexanoylglycine and suberylglycine can be diagnostic. After biochemical suspicion of MCADD, molecular genetic analysis of "ACADM" can be used to confirm the diagnosis. The analysis of MCAD activity in cultured fibroblasts can also be used for diagnosis.

In cases of sudden death where the preceding illness would not usually have been fatal, MCADD is often suspected. The autopsy will often show fatty deposits in the liver. In cases where MCADD is suspected, acylcarnitine analysis of bile and blood can be undertaken postmortem for diagnosis. Where samples are not available, residual blood from newborn screening may be helpful. Biochemical testing of asymptomatic siblings and parents may also be informative. MCADD and other fatty acid oxidation disorders have been recognized in recent years as undiagnosed causes of sudden infant death syndrome.

Less than 20 patients with MGA type I have been reported in the literature (Mol Genet Metab. 2011 Nov;104(3):410-3. Epub 2011 Jul 26.)

Symptoms can be reduced through avoidance of leucine, an amino acid. Leucine is a component of most protein-rich foods; therefore, a low-protein diet is recommended. Some isolated cases of this disorder have responded to supplemental biotin; this is not altogether surprising, consider that other biotin-related genetic disorders (such as biotinidase deficiency and holocarboxylase synthetase deficiency) can be treated solely with biotin. Individuals with these multiple carboxylase disorders have the same problem with leucine catabolism as those with 3-methylcrotonyl-CoA carboxylase deficiency.

Standard of care for treatment of CPT II deficiency commonly involves limitations on prolonged strenuous activity and the following dietary stipulations:

- The medium-chain fatty acid triheptanoin appears to be an effective therapy for adult-onset CPT II deficiency.

- Restriction of lipid intake

- Avoidance of fasting situations

- Dietary modifications including replacement of long-chain with medium-chain triglycerides supplemented with L-carnitine

A triplex tetra-primer ARMS-PCR method was developed for the simultaneous detection of C677T and A1298C polymorphisms with the A66G MTRR polymorphism in a single PCR reaction.

A 1994 study of the entire population of New South Wales (Australia) found 20 patients. Of these, 5 (25%) had died at or before 30 months of age. Of the survivors, 1 (5%) was severely disabled and the remainder had either suffered mild disability or were making normal progress in school. A 2006 Dutch study followed 155 cases and found that 27 individuals (17%) had died at an early age. Of the survivors, 24 (19%) suffered from some degree of disability, of which most were mild. All the 18 patients diagnosed neonatally were alive at the time of the follow-up.

DGUOK, POLG, and MPV17 related forms result in defects to the liver. Liver dysfunction is progressive in the majority of individuals with both forms of DGUOK-related MDS and is the most common cause of death. For children with the multi-organ form, liver transplantation provides no survival benefit.

Liver disease typically progresses to liver failure in affected children with MPV17-related MDS and liver transplantation remains the only treatment option for liver failure. Approximately half of affected children reported did not undergo liver transplantation and died because of progressive liver failure – the majority during infancy or early childhood. A few children were reported to survive without liver transplantation.

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.

The prevalence of 677T homozygozity varies with race. 18-21% of Hispanics and Southern Mediterranean populations have this variant, as do 6-14% of North American Caucasians and <2% of Blacks living outside of Africa.

The prevalence of the 1298C mutation is lower, at 4-12% for most tested populations.

A study in 2000 had identified only 24 cases of severe MTHFR deficiency (from nonsense mutations) across the whole world.