Fucosidosis is an extremely rare disorder first described in 1962 in two Italian siblings who showed progressive intellectual disability and neurological deterioration. The disease itself is extremely rare (less than 100 documented cases) only affecting 1:2,000,000, with most cases being occurring in Italy, Cuba, and the southwest U.S. The disease has three different types. Type 1 and 2 are considered severe, and Type 3 being a mild disease. Symptoms are highly variable with mild cases being able to live to within the third or fourth decade. Type 1 and 2 are both linked with mental retardation. Severe cases can develop life-threatening complications early in childhood.

Because the major accumulating glycoconjugate in fucosidosis patients is the blood group H-antigen, it is intriguing to speculate, but the evidence is not clear at this time, that blood type may affect the course of the disease.

By definition, primary immune deficiencies are due to genetic causes. They may result from a single genetic defect, but most are multifactorial. They may be caused by recessive or dominant inheritance. Some are latent, and require a certain environmental trigger to become manifest, like the presence in the environment of a reactive allergen. Other problems become apparent due to aging of bodily and cellular maintenance processes.

These are a few specialized autoimmune disorders resulting from environmental rather than genetic causes, which mimic the genotypic disorders.

Canine fucosidosis is found in the English Springer Spaniel.

Typically affecting dogs between 18 months and four years, symptoms include:

- Loss of learned behavior

- Change in temperament

- Blindness

- Loss of balance

- Deafness

- Weight loss

- From the onset, disease progress is quick and fatal.

Just like the human version, canine fucosidosis is a recessive disorder and two copies of the gene must be present, one from each parent, in order to show symptoms of the disease.

Hepatoerythropoietic porphyria is a very rare form of hepatic porphyria caused by a disorder in both genes which code Uroporphyrinogen III decarboxylase (UROD).

It has a similar presentation to porphyria cutanea tarda (PCT), but with earlier onset. In classifications which define PCT type 1 as "sporadic" and PCT type 2 as "familial", hepatoerythropoietic porphyria is more similar to type 2.

Griscelli syndrome type 2 (also known as "partial albinism with immunodeficiency") is a rare autosomal recessive syndrome characterized by variable pigmentary dilution, hair with silvery metallic sheen, frequent pyogenic infections, neutropenia, and thrombocytopenia.

This not known with certainty but is estimated to be about one per million. It appears to be more common in females than males.

The vWF gene is located on the short arm "p" of chromosome 12 (12p13.2). It has 52 exons spanning 178kbp. Types 1 and 2 are inherited as autosomal dominant traits and type 3 is inherited as autosomal recessive. Occasionally, type 2 also inherits recessively. vWD occurs in approximately 1% of the population and affects men and women equally.

The treatment of 2-Hydroxyglutaric aciduria is based on seizure control, the prognosis depends on how severe the condition is.

Von Willebrand factor is mainly active in conditions of high blood flow and shear stress. Deficiency of vWF, therefore, shows primarily in organs with extensive small vessels, such as skin, gastrointestinal tract, and uterus. In angiodysplasia, a form of telangiectasia of the colon, shear stress is much higher than in average capillaries, and the risk of bleeding is increased concomitantly.

vWF carries Factor VIII

In more severe cases of type 1 vWD, genetic changes are common within the vWF gene and are highly penetrant. In milder cases of type 1 vWD, a complex spectrum of molecular pathology may exist in addition to polymorphisms of the vWF gene alone. The individual's ABO blood group can influence presentation and pathology of vWD. Those individuals with blood group O have a lower mean level than individuals with other blood groups. Unless ABO group–specific vWF:antigen reference ranges are used, normal group O individuals can be diagnosed as type I vWD, and some individuals of blood group AB with a genetic defect of vWF may have the diagnosis overlooked because vWF levels are elevated due to blood group.

The prognosis is guarded with an overall mortality of 50%. Poor prognostic factors included HLH associated with malignancy, with half the patients dying by 1.4 months compared to 22.8 months for non-tumour associated HLH patients.

Secondary HLH in some individuals may be self-limited because patients are able to fully recover after having received only supportive medical treatment (i.e., IV immunoglobulin only). However, long-term remission without the use of cytotoxic and immune-suppressive therapies is unlikely in the majority of adults with HLH and in those with involvement of the central nervous system (brain and/or spinal cord).

Glutaric acidemia type 2 often appears in infancy as a sudden metabolic crisis, in which acidosis and low blood sugar (hypoglycemia) cause weakness, behavior changes, and vomiting. There may also be enlargement of the liver, heart failure, and a characteristic odor resembling that of sweaty feet. Some infants with glutaric acidemia type 2 have birth defects, including multiple fluid-filled growths in the kidneys (polycystic kidneys). Glutaric acidemia type 2 is a very rare disorder. Its precise incidence is unknown. It has been reported in several different ethnic groups.

The disease is typically progressive, leading to fulminant liver failure and death in childhood, in the absence of liver transplantation. Hepatocellular carcinoma may develop in PFIC-2 at a very early age; even toddlers have been affected.

The D2 form is rare, with symptoms including macrocephaly, cardiomyopathy, mental retardation, hypotonia, and cortical blindness. It is caused by recessive mutations in "D2HGDH" (type I) or by dominant gain-of-function mutations in "IDH2" (type II).

The fifth type of hyper-IgM syndrome has been characterized in three patients from France and Japan. The symptoms are similar to hyper IgM syndrome type 2, but the AICDA gene is intact. These three patients instead had mutations in the catalytic domain of uracil-DNA glycosylase, an enzyme that removes uracil from DNA. In both type 2 and type 5 hyper-IgM syndromes, the patients are profoundly deficient in IgG and IgA because the B cells can't carry out the recombination steps necessary to class-switch.

Glutaric acidemia type 2 is an autosomal recessive metabolic disorder that is characterised by defects in the ability of the body to use proteins and fats for energy. Incompletely processed proteins and fats can build up, leading to a dangerous chemical imbalance called acidosis.

Howel–Evans syndrome is an extremely rare condition involving thickening of the skin in the palms of the hands and the soles of the feet (hyperkeratosis). This familial disease is associated with a high lifetime risk of esophageal cancer. For this reason, it is sometimes known as tylosis with oesophageal cancer (TOC).

The condition is inherited in an autosomal dominant manner, and it has been linked to a mutation in the "RHBDF2" gene. It was first described in 1958.

This condition is inherited as an autosomal dominant syndrome and characterized by palmoplantar keratoderma, oral precursor lesions particularly on the gums (leukoplakia) and a high lifetime risk of esophageal cancer (95% develop esophageal cancer by the age of 65). Relapsing cutaneous horns of the lips has been reported in this condition.

There are several types of this condition have been described – epidermolytic (Vörner type) and non-epidermolytic. Another classification divides these into an early onset type (type B) which occurs in the first year of life and is usually benign and a type A tylosis which occurs between the ages of 5 and 15 years and is strongly associated with esophageal cancer.

Cytoglobin gene expression in oesphageal biopsies is significantly reduced (70% reduction) in this condition. The mechanism of this change is not known.

D-Bifunctional protein deficiency (officially called 17β-hydroxysteroid dehydrogenase IV deficiency) is an autosomal recessive peroxisomal fatty acid oxidation disorder. Peroxisomal disorders are usually caused by a combination of peroxisomal assembly defects or by deficiencies of specific peroxisomal enzymes. The peroxisome is an organelle in the cell similar to the lysosome that functions to detoxify the cell. Peroxisomes contain many different enzymes, such as catalase, and their main function is to neutralize free radicals and detoxify drugs, such as alcohol. For this reason peroxisomes are ubiquitous in the liver and kidney. D-BP deficiency is the most severe peroxisomal disorder, often resembling Zellweger syndrome.

Characteristics of the disorder include neonatal hypotonia and seizures, occurring mostly within the first month of life, as well as visual and hearing impairment. Other symptoms include severe craniofacial disfiguration, psychomotor delay, and neuronal migration defects. Most onsets of the disorder begin in the gestational weeks of development and most affected individuals die within the first two years of life.

Congenital generalized lipodystrophy (also known as Berardinelli–Seip syndrome) is an extremely rare autosomal recessive skin condition, characterized by an extreme scarcity of fat in the subcutaneous tissues. It is a type of lipodystophy disorder where the magnitude of fat loss determines the severity of metabolic complications. Only 250 cases of the condition have been reported, and it is estimated that it occurs in 1 in 10 million people worldwide.

All types of Griscelli syndrome have distinctive skin and hair coloring.

Type 1 is associated with eurological abnormalities. These include delayed development, intellectual disability, seizures, hypotonia and eye abnormalities.

Type 2 - unlike type 1 - is not associated primary neurological disease but is associated with an uncontrolled T lymphocyte expansion and macrophage activation syndrome. It is often associated with the hemophagocytic syndrome. This latter condition may be fatal in the absence of bone marrow transplantation.

Persons with type 3 have the typical light skin and hair coloring but are otherwise normal.

Hyper IgM Syndrome Type 2 is a rare disease. Unlike other hyper-IgM syndromes, the Type 2 patients identified thus far did not present with a history of opportunistic infections. One would expect opportunistic infections in any immunodeficiency syndrome. The putative genetic lesion is in the AICDA gene found at 12p13. The patients have three common findings:

- the absence of immunoglobulin class switch recombination

- the lack of immunoglobulin somatic hypermutations, and

- lymph node hyperplasia caused by the presence of giant germinal centers.

Familial partial lipodystrophy (FPL), also known as Köbberling–Dunnigan syndrome, is a rare genetic metabolic condition characterized by the loss of subcutaneous fat.

FPL also refers to a rare metabolic condition in which there is a loss of subcutaneous fat in the arms, legs and lower torso. The upper section of the body, face, neck, shoulders, back and trunk carry an excess amount of fat.

As the body is unable to store fat correctly this leads to fat around all the vital organs and in the blood (triglycerides). This results in heart problems, cirrhosis of the liver, lipoatrophic diabetes, and pancreatitis, along with various other complications.

Hemophagocytic lymphohistiocytosis (HLH), also known as haemophagocytic lymphohistiocytosis (British spelling), and hemophagocytic or haemophagocytic syndrome, is an uncommon hematologic disorder seen more often in children than in adults. It is a life-threatening disease of severe hyperinflammation caused by uncontrolled proliferation of activated lymphocytes and macrophages, characterised by proliferation of morphologically benign lymphocytes and macrophages that secrete high amounts of inflammatory cytokines. It is classified as one of the cytokine storm syndromes.

MODY 6 is a form of maturity onset diabetes of the young.

MODY 6 arises from mutations of the gene for the transcription factor referred to as neurogenic differentiation 1. The gene is on chromosome 2 in a region of the p arm known as IDDM7 because it includes genes affecting susceptibility to type 1 diabetes. NeuroD1 promotes transcription of the insulin gene as well as some genes involved in formation of beta cells and parts of the nervous system.

This is also one of the rarer forms of MODY. Only 3 kindreds with mutations causing MODY6 have been identified so far. In both, some of the members had more typical type 2 diabetes rather than MODY, and the reasons for the difference of expression have not been worked out. Most of the family members with diabetes were diagnosed after age 40, but a few required insulin for blood sugar control.