No treatment is available for most of these disorders. Mannose supplementation relieves the symptoms in PMI-CDG (CDG-Ib) for the most part, even though the hepatic fibrosis may persist. Fucose supplementation has had a partial effect on some SLC35C1-CDG (CDG-IIc or LAD-II) patients.

A diagnosis can be made by an evaluation of medical history and clinical observation. The Beighton criteria are widely used to assess the degree of joint hypermobility. DNA and biochemical studies can help identify affected individuals. Diagnostic tests include collagen gene mutation testing, collagen typing via skin biopsy, echocardiogram, and lysyl hydroxylase or oxidase activity. However, these tests are not able to confirm all cases, especially in instances of an unmapped mutation, so clinical evaluation by a geneticist remains essential. If there are multiple affected individuals in a family, it may be possible to perform prenatal diagnosis using a DNA information technique known as a linkage study. There is poor knowledge about EDS among practitioners.

A congenital disorder of glycosylation (previously called carbohydrate-deficient glycoprotein syndrome) is one of several rare inborn errors of metabolism in which glycosylation of a variety of tissue proteins and/or lipids is deficient or defective. Congenital disorders of glycosylation are sometimes known as CDG syndromes. They often cause serious, sometimes fatal, malfunction of several different organ systems (especially the nervous system, muscles, and intestines) in affected infants. The most common subtype is CDG-Ia (also referred to as PMM2-CDG) where the genetic defect leads to the loss of phosphomannomutase 2, the enzyme responsible for the conversion of mannose-6-phosphate into mannose-1-phosphate.

The outlook for individuals with EDS depends on the type of EDS they have. Symptoms vary in severity, even within one sub-type, and the frequency of complications changes individually. Some people have negligible symptoms while others are severely restricted in their daily life. Extreme joint instability, chronic musculoskeletal pain, degenerative joint disease, frequent injuries, and spinal deformities may limit mobility. Severe spinal deformities may affect breathing. In the case of extreme joint instability, dislocations may result from simple tasks such as rolling over in bed or turning a doorknob. Secondary conditions such as autonomic dysfunction or cardiovascular problems, occurring in any type, can affect prognosis and quality of life. Severe mobility-related disability is seen more often in Hypermobility-type than in Classical-type or Vascular-type.

Although all types are potentially life-threatening, the majority of individuals will have a normal lifespan. However, those with blood vessel fragility have a high risk of fatal complications. Arterial rupture is the most common cause of sudden death in EDS. Spontaneous arterial rupture most often occurs in the second or third decade, but can occur at any time. The median life-expectancy in the population with Vascular EDS is 48 years.

Diagnosis is mostly clinical and radiological. Technetium skeletal scintigrams are occasionally used to determine number of exostoses.

De Barsy syndrome is a rare autosomal recessive genetic disorder. Symptoms include cutis laxa (loose hanging skin) as well as other eye, musculoskeletal, and neurological abnormalities. It is usually progressive, manifesting side effects that can include clouded corneas, cataracts, short stature, dystonia, or progeria (premature aging).

It was first described in 1967 by De Barsy et al. and, as of 2011, there have been 27 cases reported worldwide. The genes that cause De Barsy syndrome have not been identified yet, although several studies have narrowed down the symptoms' cause. A study by Reversade et al. has shown that a mutation in PYCR1, the genetic sequence that codes for mitochondrial enzymes that break down proline, are prevalent in cases of autosomal recessive cutis laxa (ARCL), a condition very similar to De Barsy syndrome. A study by Leao-Teles et al. has shown that De Barsy syndrome may be related to mutations in ATP6V0A2 gene, known as ATP6V0A2-CDG by the new naming system.

Alternative names for De Barsy syndrome include corneal clouding-cutis laxa-mental retardation, cutis laxa-growth deficiency syndrome, De Barsy–Moens–Diercks syndrome, and progeroid syndrome of De Barsy.

Some parents of children with MHE have observed autism-like social problems in their children. To explore those observations more deeply, a 2012 study by the Sanford-Burnham Medical Research Institute used a mouse model of MHE to observe cognitive function. The findings indicated that the mutant mice endorsed three autistic characteristics: social impairment, impairments in ultrasonic vocalization, and repetitive behavior.

The differential diagnosis of congenital hyperinsulinism is consistent with PMM2-CDG, as well as several syndromes. Among other DDx we find the following that are listed:

- MPI-CDG

- Beckwith-Wiedemann syndrome

- Sotos syndrome

- Usher 1 syndromes

In terms of the investigation of congenital hyperinsulinism, valuable diagnostic information is obtained from a blood sample drawn during hypoglycemia, detectable amounts of insulin during hypoglycemia are abnormal and indicate that hyperinsulinism is likely to be the cause. Inappropriately low levels of free fatty acids and ketones provide additional evidence of insulin excess. An additional piece of evidence indicating hyperinsulinism is a usually high requirement for intravenous glucose to maintain adequate glucose levels, the minimum glucose required to maintain a plasma glucose above 70 mg/dl. A GIR above 8 mg/kg/minute in infancy suggests hyperinsulinism. A third form of evidence suggesting hyperinsulinism is a rise of the glucose level after injection of glucagon at the time of the low glucose.

Diagnostic efforts then shift to determining the type- elevated ammonia levels or abnormal organic acids can indicate specific, rare types. Intrauterine growth retardation and other perinatal problems raise the possibility of transience, while large birthweight suggests one of the more persistent conditions. Genetic screening is now available within a useful time frame for some of the specific conditions.It is worthwhile to identify the minority of severe cases with focal forms of hyperinsulinism because these can be completely cured by partial pancreatectomy. A variety of pre-operative diagnostic procedures have been investigated but none has been established as infallibly reliable. Positron emission tomography is becoming the most useful imaging technique.