A combination of clinical findings and laboratory tests are used to diagnose Rabson-Mendenhall Syndrome. Initially, individuals are screened for symptoms and have their blood sugar levels analyzed. The two principle tests used to determine insulin resistance are the fasting plasma glucose test (FPG) and the oral glucose tolerance test (GTT). Results from a patient with severe insulin resistance will show values exceeding healthy ranges (≤99 mg/dL for FPG and ≤139 mg/dL for GTT) by over 50 units. A genetic history is also established to determine risk of recurrence in the family. Based on the combination of these findings, an appropriate diagnosis is made.

Rabson–Mendenhall syndrome is commonly associated with Donohue syndrome, also known as "Leprechaunism". Both diseases are autosomal recessive disorders caused by mutations on chromosome 19. Severe insulin resistance and an irregular enlargement of the genitalia are also overlapping symptoms.

The ring 20 abnormality may be limited to as few as 5% of cells, so a screen for chromosomal mosaicism is critical. Newer array technology will not detect the ring chromosome and the standard metaphase chromosome analysis has been recommended. A karyotype analysis examining at least 50 cells should be requested to properly detect mosaicism.

The World Anti-Doping Agency (WADA) is the main regulatory organization looking into the issue of the detection of gene doping. Both direct and indirect testing methods are being researched by the organization. Directly detecting the use of gene therapy usually requires the discovery of recombinant proteins or gene insertion vectors, while most indirect methods involve examining the athlete in an attempt to detect bodily changes or structural differences between endogenous and recombinant proteins.

Indirect methods are by nature more subjective, as it becomes very difficult to determine which anomalies are proof of gene doping, and which are simply natural, though unusual, biological properties. For example, Eero Mäntyranta, an Olympic cross country skier, had a mutation which made his body produce abnormally high amounts of red blood cells. It would be very difficult to determine whether or not Mäntyranta's red blood cell levels were due to an innate genetic advantage, or an artificial one.

Criteria for CSF abnormalities:

- Increased opening pressure (> 200mm of H2O)

- Increased Leukocytes (>4/mm3)

- Elevated protein (>50 mg/dL)

- Decreased glucose (<60 mg/dL)

Tumor Markers:

- Carcinoembryonic antigin (CEA)

- alpha-fetoprotein

- beta-human chorionic gonadotropin

- carbohydrate antigen19-9

- creatine-kinase BB

- isoenzyme

- tissue polypeptide antigen

- beta2-microglobulin,

- beta-glucoronidase

- lactate dehydrogenase isoenzyme-5

- vascular endothelial growth factor

These markers can be good indirect indicator of NM but most are not sensitive enough to improve cytogical diagnosis.

Avoiding false-negative

- Draw CSF from symptomatic or radiographically demonstrated disease.

- Draw large amount of CSF (>10.5mL).

- Don't delay processing of specimen.

- Obtain at least 2 samples. The first sample has diagnostic sensitivity of 54% but with repeated sampling, diagnostic sensitivity is increased to 91%.

Ideal procedure for diagnosis:

Lumbar puntures --> cranial MRI --> spinal MRI --> radioisotope CSF flow --> ventricular or lateral cervical spine CSF analysis (if previous step yields no definitive answer)

Since elevated PGE2 levels are correlated with PDP, urinary PGE2 can be a useful biomarker for this disease. Additionally, HPGD mutation analyses are relatively cheap and simple and may prove to be useful in early investigation in patients with unexplained clubbing or children presenting PDP-like features. Early positive results can prevent expensive and longtime tests at identifying the pathology.

For the follow-up of PDP disease activity, bone formation markers such as TAP, BAP, BGP, carbodyterminal propeptide of type I procallagen or NTX can play an important role. Other biomarkers that can be considered are IL-6 and receptor activator of NF-κB ligand (RANKL), which are associated with increased bone resorption in some patients. However, further investigation is needed to confirm this use of disease monitoring.

Prostaglandin E2 may also be raised in patients with lung cancer and finger clubbing. This may be related to raised levels of cyclooxygenase-2, an enzyme involved in the metabolism of prostaglandins. A similar association has been noted in cystic fibrosis.

Pyruvate dehydrogenase deficiency can be diagnosed via the following methods:

- Blood test (Lactate and pyruvate levels)

- Urine analysis

- Magnetic resonance spectroscopy

- MRI

The easiest way to diagnose PDP is when pachydermia, finger clubbing and periostosis of the long bones are present. New bone formation under the periosteum can be detected by radiographs of long bones. In order diagnose PDP, often other diseases must be excluded. For example, to exclude secondary hypertrophic osteoarthropathy, any signs of cardiovascular, pulmonary, hepatic, intestinal and mediastinal diseases must be absent. MRI and ultrasound also have characterictic findings.

Skin biopsy is another way to diagnose PDP. However, it is not a very specific method, because other diseases share the same skin alterations with PDP, such as myxedema and hypothyroidism. In order to exclude these other diseases, hormonal studies are done. For example, thyrotropin and growth hormone levels should be examined to exclude thyroid acropachy and acrome. However, skin biopsy helps to diagnose PDP in patients without skin manifestations.

When clubbing is observed, it is helpful to check whether acroosteolysis of distal phalanges of fingers is present. This is useful to diagnose PDP, because the combination of clubbing and acroosteolysis is only found in PDP and Cheney’s syndrome.

The differential diagnosis of pyruvate dehydrogenase deficiency can consist of either D-Lactic acidosis or abnormalities associated with gluconeogenesis.

The diagnosis of NM is based on the detection of malignant cells in the CSF, the demonstration of leptomeningeal tumor cell deposits on neuroimaging, or both. CSF examination is the most useful diagnostic tool for NM. Patients with suspected NM should undergo one or two lumbar punctures, cranial magnetic resonance imaging (MRI), spinal MRI, and a radioisotope CSF flow study to rule out sites of CSF block. If the cytology remains negative and radiological studies are not definitive, consideration may be given to ventricular or lateral cervical spine CSF analysis based on the suspected site of predominant disease. Consideration of signs, symptoms, and neuroimaging can help with the placement to where CSF is drawn. Median time of diagnosis from initial primary cancer diagnosis is between 76 days and 17 months. NM diagnosis has been increasing and will continue to increase due to better primary care and longer survival time of cancer patients.

Difficulties in Diagonsis:

NM is multifocal and CSF at a particular site may show no abnormalities if the pathological site is far away. Only 50% of those suspected with NM are actually diagnosed with NM and only the presence of malignant cells in the CSF is diagnosis conclusive.

Techniques:

- MRI: Meningeal findings are described with the following characteristics: Nodular meningeal tumor, meningeal thickening >3 mm and a subjectively strong contrast enhancement. A smooth contrast enhancement of the meninges was judged to be typical for inflammatory, nonneoplastic meningitis.

- CSF cytology: is performed after drawing the CSF by lumbar puncture.

- Cytogenetic: measures chromosomal content of cells and fluorescence in situ hybridization which detects numerical and structural genetic aberrations as a sign of malignancy. This is especially useful for liquid tumors such as leukemia and lymphoma. Some of the techniques that achieve this are flow cytometry and DNA single-cell cytometry. However, cytogenetic only assist in diagnosis and is less preferred.

- Meningeal Biopsy: may be performed when all of the above criteria is inconclusive. Biopsy is only effective when performed at the region where there's enhancement on the MRI.

Several different types of magnetic resonance imaging (MRI) may be employed in diagnosis: MRI without contrast, Gd contrast enhanced T1-weighted MRI (GdT1W) or T2-weighted enhanced MRI (T2W or T2*W). Non-contrast enhanced MRI is considerably less expensive than any of the contrast enhanced MRI scans. The gold standard in diagnosis is GdT1W MRI.

The reliability of non-contrast enhanced MRI is highly dependent on the sequence of scans, and the experience of the operator.

Microlissencephaly can be diagnosed by prenatal MRI. MRI is better than ultrasound when it comes to detecting microlissencephaly or MSGP prenatally.

The ideal time for proper prenatal diagnosis is between the 34th and 35th gestational week which is the time when the secondary gyration normally terminates. In microlissencephaly cases, the primary sulci would be unusually wide and flat while secondary sulci would be missing.

At birth, lissencephaly with a head circumference of less than minus three standard deviations (< –3 SD) is considered microlissencephaly.

Although genetic diagnosis in patients with MLIS is challenging, exome sequencing has been suggested to be a powerful diagnostic tool.

Rabson and Mendenhall described 3 sibling (2 girls, 1 boy) who initially presented with dental and skin abnormalities, abdominal distention, and phallic enlargement. The children demonstrated early dentition, a coarse, senile-appearing , and striking hirsutism. An "adult growth of hair of head" at 5 years of age was pictured in the case of one of the girls. In the older girl the genitalia were large enough at the age of 6 months to permit vaginal examination for diagnosis of a left ovarian tumor which was removed soon afterward. The children were mentally precocious. Prognathism and very thick fingernails as well as acanthosis nigricans were also described. Insulin-resistant diabetes developed, and the patients died during childhood of ketoacidosis and intercurrent infections. At autopsy pineal hyperplasia was found in all three.

Biologically, infants display fasting hypoglycemia, postprandial hyperglycemia and hyperinsulinemia, which progress to permanent hyperglycemia and recurrent diabetic ketoacidosis.

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.

Limited data is available for the long-term prognosis of ring chromosome 20 syndrome since only over 60 patients with this syndrome have been reported in published literature. Optimal control of seizures appears to be the determining factor, but early diagnosis and a comprehensive management plan with multidisciplinary support is also thought be to be important.

The World Anti-Doping Agency (WADA) determined that non therapeutic form of genetic manipulation for enhancement of athletic performance is not allowed in sport. The WADA code implemented guidelines to determine if said technology should be prohibited in sport. If two of the three conditions are met, then the technology is prohibited in sport; harmful to one's health, performance enhancing, and/or against the "spirit of sport". The high risks associated with gene therapy can be outweighed by the potential save the lives of individuals with diseases. According to Alain Fischer, who was involved in clinical trials of gene therapy in children with severe combined immunodeficiency, "Only people who are dying would have reasonable grounds for using it. Using gene therapy for doping is ethically unacceptable and scientifically stupid." As seen with past cases, including the steroid tetrahydrogestrinone THG, athletes may choose to incorporate risky genetic technologies into their training regimes.

The mainstream perspective is that gene doping is dangerous and unethical, as is any application of a therapeutic intervention for non-therapeutic or enhancing purposes, and that it compromises the ethical foundation of medicine and the spirit of sport. Others, who support human enhancement on broader grounds, or who see a false dichotomy between "natural" and "artificial" or a denial of the role of technology in improving athletic performance, do not oppose or support gene doping.

Before the advent of MRI, electronystagmography and Computed Tomography were employed for diagnosis of acoustic neuroma.

Diagnosis often can be made through clinical examination and urine tests (excess mucopolysaccharides are excreted in the urine). Enzyme assays (testing a variety of cells or body fluids in culture for enzyme deficiency) are also used to provide definitive diagnosis of one of the mucopolysaccharidoses. Prenatal diagnosis using amniocentesis and chorionic villus sampling can verify if a fetus either carries a copy of the defective gene or is affected with the disorder. Genetic counseling can help parents who have a family history of the mucopolysaccharidoses determine if they are carrying the mutated gene that causes the disorders.

Microlissencephaly is considered a more severe form than microcephaly with simplified gyral pattern. Microlissencephaly is characterized by a smooth cortical surface (absent sulci and gyri) with a thickened cortex (> 3 mm) and is usually associated with other congenital anomalies. Microcephaly with a simplified gyral pattern has too few sulci and normal cortical thickness (3 mm) and is usually an isolated anomaly.

The detection of tumours specific to VHL disease is important in the disease's diagnosis. In individuals with a family history of VHL disease, one hemangioblastoma, pheochromocytoma or renal cell carcinoma may be sufficient to make a diagnosis. As all the tumours associated with VHL disease can be found sporadically, at least two tumours must be identified to diagnose VHL disease in a person without a family history.

Genetic diagnosis is also useful in VHL disease diagnosis. In hereditary VHL, disease techniques such as southern blotting and gene sequencing can be used to analyse DNA and identify mutations. These tests can be used to screen family members of those afflicted with VHL disease; "de novo" cases that produce genetic mosaicism are more difficult to detect because mutations are not found in the white blood cells that are used for genetic analysis.

Branchio-oculo-facial syndrome is difficult to diagnose because it has incomplete penetrance. It is often misdiagnosed as branchio-oto-renal syndrome because of their similarities in symptoms.

It was estimated that only about 50 cases of BOFS have been documented in the medical literature as of 2004.

Seven distinct clinical types and numerous subtypes of the mucopolysaccharidoses have been identified. Although each mucopolysaccharidosis (MPS) differs clinically, most patients generally experience a period of normal development followed by a decline in physical and/or mental function. (Note: MPS-V and MPS-VIII are no longer in use as designations for any disease.)

The diagnosis of Albright's hereditary osteodystrophy is based on the following exams below:

- CBC

- Urine test

- MRI

There are no methods for preventing the manifestation of the pathology of MSUD in infants with two defective copies of the BCKD gene. However, genetic counselors may consult with couples to screen for the disease via DNA testing. DNA testing is also available to identify the disease in an unborn child in the womb.

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.