Sandhoff disease symptoms are clinically indeterminable from Tay–Sachs disease. The classic infantile form of the disease has the most severe symptoms and is incredibly hard to diagnose at this early age. The first signs of symptoms begin before 6 months of age and the parents’ notice when the child begins regressing in their development. If the children had the ability to sit up by themselves or crawl they will lose this ability. This is caused by a slow deterioration of the muscles in the child’s body from the buildup of GM2 gangliosides. Since the body is unable to create the enzymes it needs within the central nervous system it is unable to attach to these gangliosides to break them apart and make them non-toxic. With this buildup there are several symptoms that begin to appear such as muscle/motor weakness, sharp reaction to loud noises, blindness, deafness, inability to react to stimulants, respiratory problems and infections, mental retardation, seizures, cherry red spots in the retina, enlarged liver and spleen (hepatosplenomegaly), pneumonia, or bronchopneumonia.

The other two forms of Sandhoff disease have similar symptoms but to a lesser extent. Adult and juvenile forms of Sandhoff disease are more rare than the infantile form. In these cases victims suffer cognitive impairment (retardation) and a loss of muscle coordination that impairs and eventually destroys their ability to walk; the characteristic red spots in the retina also develop. The adult form of the disease, however, is sometimes milder, and may only lead to muscle weakness that impairs walking or the ability to get out of bed.

The GM2 gangliosidoses are a group of three related genetic disorders that result from a deficiency of the enzyme beta-hexosaminidase. This enzyme catalyzes the biodegradation of fatty acid derivatives known as gangliosides. The diseases are better known by their individual names.

Beta-hexosaminidase is a vital hydrolytic enzyme, found in the lysosomes, that breaks down lipids. When beta-hexosaminidase is no longer functioning properly, the lipids accumulate in the nervous tissue of the brain and cause problems. Gangliosides are made and biodegraded rapidly in early life as the brain develops. Except in some rare, late-onset forms, the GM2 gangliosidoses are fatal.

All three disorders are rare in the general population. Tay-Sachs disease has become famous as a public health model because an enzyme assay test for TSD was discovered and developed in the late 1960s and early 1970s, providing one of the first "mass screening" tools in medical genetics. It became a research and public health model for understanding and preventing all autosomal genetic disorders.

Tay-Sachs disease, AB variant, and Sandhoff disease might easily have been defined together as a single disease, because the three disorders are associated with failure of the same metabolic pathway and have the same outcome. Classification and naming for many genetic disorders reflects history, because most diseases were first observed and classified based on biochemistry and pathophysiology before genetic diagnosis was available. However, the three GM2 gangliosidoses were discovered and named separately. Each represents a distinct molecular point of failure in a subunit that is required for activation of the enzyme.

Sandhoff disease, also known as Sandhoff–Jatzkewitz disease, variant 0 of GM2-Gangliosidosis or Hexosaminidase A and B deficiency, is a lysosomal genetic, lipid storage disorder caused by the inherited deficiency to create functional beta-hexosaminidases A and B. These catabolic enzymes are needed to degrade the neuronal membrane components, ganglioside GM2, its derivative GA2, the glycolipid globoside in visceral tissues, and some oligosaccharides. Accumulation of these metabolites leads to a progressive destruction of the central nervous system and eventually to death. The rare autosomal recessive neurodegenerative disorder is clinically almost indistinguishable from Tay–Sachs disease, another genetic disorder that disrupts beta-hexosaminidases A and S. There are three subsets of Sandhoff disease based on when first symptoms appear: classic infantile, juvenile and adult late onset.

Tay–Sachs disease is a rare autosomal recessive genetic disorder that causes a progressive deterioration of nerve cells and of mental and physical abilities that begins around six months of age and usually results in death by the age of four. It is the most common of the GM2 gangliosidoses. The disease occurs when harmful quantities of cell membrane gangliosides accumulate in the brain's nerve cells, eventually leading to the premature death of the cells.

Methylenetetrahydrofolate reductase (MTHFR) deficiency is the most common genetic cause of elevated serum levels of homocysteine (hyperhomocysteinemia). It is caused by genetic defects in MTHFR, which is an important enzyme in the methyl cycle.

Common variants of MTHFR deficiency are asymptomatic and have only minor effects on disease risk. Severe variants (from nonsense mutations) are vanishingly rare.

The common MTHFR deficiencies are usually asymptomatic, although the 677T variant can cause a mildly increased risk of some diseases.

For individuals homozygous in the 677T variant, there is a mildly elevated risk of thromboembolism (odds ratio 1.2), and stroke (odds ratio 1.26). There is also an elevated risk of neural tube defects among children of individuals with the C677T polymorphism (odds ratio 1.38).

For cardiovascular risk, common MTHFR deficiencies were once thought to be associated but meta-analyses indicate that correlation this was an artifact of publication bias.

A lipid storage disorder (or lipidosis) can be any one of a group of inherited metabolic disorders in which harmful amounts of fats or lipids accumulate in some of the body’s cells and tissues. People with these disorders either do not produce enough of one of the enzymes needed to metabolize and break down lipids or they produce enzymes that do not work properly. Over time, this excessive storage of fats can cause permanent cellular and tissue damage, particularly in the brain, peripheral nervous system, liver, spleen and bone marrow.

Inside cells under normal conditions, lysosomes convert, or metabolize, lipids and proteins into smaller components to provide energy for the body.

The symptoms of LSD vary, depending on the particular disorder and other variables such as the age of onset, and can be mild to severe. They can include developmental delay, movement disorders, seizures, dementia, deafness, and/or blindness. Some people with LSDhave enlarged livers (hepatomegaly) and enlarged spleens (splenomegaly), pulmonary and cardiac problems, and bones that grow abnormally.

Gangliosidosis contains different types of lipid storage disorders caused by the accumulation of lipids known as gangliosides. There are two distinct genetic causes of the disease. Both are autosomal recessive and affect males and females equally.

Signs and symptoms of GM2-gangliosidosis, AB variant are identical with those of infantile Tay-Sachs disease, except that enzyme assay testing shows normal levels of hexosaminidase A. Infantile Sandhoff disease has similar symptoms and prognosis, except that there is deficiency of both hexosaminidase A and hexosaminidase B. Infants with this disorder typically appear normal until the age of 3 to 6 months, when development slows and muscles used for movement weaken. Affected infants lose motor skills such as turning over, sitting, and crawling. As the disease progresses, infants develop seizures, vision and hearing loss, mental retardation, and paralysis.

An ophthalmological abnormality called a cherry-red spot, which can be identified with an eye examination, is characteristic of this disorder. This cherry-red spot is the same finding that Warren Tay first reported in 1881, when he identified a case of Tay-Sachs disease, and it has the same etiology.

The prognosis for AB variant is the same as for infantile Tay-Sachs disease. Children with AB variant die in infancy or early childhood.

Other lipid storage disorders that are generally not classified as sphingolipidoses include fucosidosis, Schindler disease and Wolman disease.

A vitamin deficiency can cause a disease or syndrome known as an avitaminosis or hypovitaminosis. This usually refers to a long-term deficiency of a vitamin. When caused by inadequate nutrition it can be classed as a "primary deficiency", and when due to an underlying disorder such as malabsorption it can be classed as a "secondary deficiency". An underlying disorder may be metabolic as in a defect converting tryptophan to niacin. It can also be the result of lifestyle choices including smoking and alcohol consumption.

Examples are vitamin A deficiency, folate deficiency, scurvy, vitamin D deficiency, vitamin E deficiency, and vitamin K deficiency. In the medical literature, any of these may also be called by names on the pattern of "hypovitaminosis" or "avitaminosis" + "[letter of vitamin]", for example, hypovitaminosis A, hypovitaminosis C, hypovitaminosis D.

Conversely hypervitaminosis is the syndrome of symptoms caused by over-retention of fat-soluble vitamins in the body.

- Vitamin A deficiency can cause keratomalacia.

- Thiamine (vitamin B1) deficiency causes beriberi and Wernicke–Korsakoff syndrome.

- Riboflavin (vitamin B2) deficiency causes ariboflavinosis.

- Niacin (vitamin B3) deficiency causes pellagra.

- Pantothenic acid (vitamin B5) deficiency causes chronic paresthesia.

- Vitamin B6

- Biotin (vitamin B7) deficiency negatively affects fertility and hair/skin growth. Deficiency can be caused by poor diet or genetic factors (such as mutations in the BTD gene, see multiple carboxylase deficiency).

- Folate (vitamin B9) deficiency is associated with numerous health problems. Fortification of certain foods with folate has drastically reduced the incidence of neural tube defects in countries where such fortification takes place. Deficiency can result from poor diet or genetic factors (such as mutations in the MTHFR gene that lead to compromised folate metabolism).

- Vitamin B12 (cobalamin) deficiency can lead to pernicious anemia, megaloblastic anemia, subacute combined degeneration of spinal cord, and methylmalonic acidemia among other conditions.

- Vitamin C (ascorbic acid) short-term deficiency can lead to weakness, weight loss and general aches and pains. Longer-term depletion may affect the connective tissue. Persistent vitamin C deficiency leads to scurvy.

- Vitamin D (cholecalciferol) deficiency is a known cause of rickets, and has been linked to numerous health problems.

- Vitamin E deficiency causes nerve problems due to poor conduction of electrical impulses along nerves due to changes in nerve membrane structure and function.

- Vitamin K (phylloquinone or menaquinone) deficiency causes impaired coagulation and has also been implicated in osteoporosis

Lysosomal storage diseases (LSDs; ) are a group of about 50 rare inherited metabolic disorders that result from defects in lysosomal function. Lysosomes are sacs of enzymes within cells that digest large molecules and pass the fragments on to other parts of the cell for recycling. This process requires several critical enzymes. If one of these enzymes is defective, because of a mutation, the large molecules accumulate within the cell, eventually killing it.

Lysosomal storage disorders are caused by lysosomal dysfunction usually as a consequence of deficiency of a single enzyme required for the metabolism of lipids, glycoproteins (sugar-containing proteins), or so-called mucopolysaccharides. Individually, LSDs occur with incidences of less than 1:100,000; however, as a group, the incidence is about 1:5,000 - 1:10,000. Most of these disorders are autosomal recessively inherited such as Niemann–Pick disease, type C, but a few are X-linked recessively inherited, such as Fabry disease and Hunter syndrome (MPS II).

The lysosome is commonly referred to as the cell's recycling center because it processes unwanted material into substances that the cell can use. Lysosomes break down this unwanted matter by enzymes, highly specialized proteins essential for survival. Lysosomal disorders are usually triggered when a particular enzyme exists in too small an amount or is missing altogether. When this happens, substances accumulate in the cell. In other words, when the lysosome does not function normally, excess products destined for breakdown and recycling are stored in the cell.

Like other genetic disorders, individuals inherit lysosomal storage diseases from their parents. Although each disorder results from different gene mutations that translate into a deficiency in enzyme activity, they all share a common biochemical characteristic – all lysosomal disorders originate from an abnormal accumulation of substances inside the lysosome.

LSDs affect mostly children and they often die at a young and unpredictable age, many within a few months or years of birth. Many other children die of this disease following years of suffering from various symptoms of their particular disorder.

Tay–Sachs disease is typically first noticed in infants around 6 months old displaying an abnormally strong response to sudden noises or other stimulus, known as the "startle response," because they are startled. There may also be listlessness or muscle stiffness (hypertonia). The disease is classified into several forms, which are differentiated based on the onset age of neurological symptoms.

- Infantile Tay–Sachs disease. Infants with Tay–Sachs disease appear to develop normally for the first six months after birth. Then, as neurons become distended with gangliosides, a relentless deterioration of mental and physical abilities begins. The child may become blind, deaf, unable to swallow, atrophied, and paralytic. Death usually occurs before the age of four.

- Juvenile Tay–Sachs disease. Juvenile Tay–Sachs disease is rarer than other forms of Tay–Sachs, and usually is initially seen in children between two and ten years old. People with Tay–Sachs disease develop cognitive and motor skill deterioration, dysarthria, dysphagia, ataxia, and spasticity. Death usually occurs between the age of five to fifteen years.

- Adult/Late-Onset Tay–Sachs disease. A rare form of this disease, known as Adult-Onset or Late-Onset Tay–Sachs disease, usually has its first symptoms during the 30s or 40s. In contrast to the other forms, late-onset Tay–Sachs disease is usually not fatal as the effects can stop progressing. It is frequently misdiagnosed. It is characterized by unsteadiness of gait and progressive neurological deterioration. Symptoms of late-onset Tay–Sachs – which typically begin to be seen in adolescence or early adulthood – include speech and swallowing difficulties, unsteadiness of gait, spasticity, cognitive decline, and psychiatric illness, particularly a schizophrenia-like psychosis. People with late-onset Tay–Sachs may become full-time wheelchair users in adulthood.

Until the 1970s and 1980s, when the disease's molecular genetics became known, the juvenile and adult forms of the disease were not always recognized as variants of Tay–Sachs disease. Post-infantile Tay–Sachs was often misdiagnosed as another neurological disorder, such as Friedreich's ataxia.

GM2-gangliosidosis, AB variant is a rare, autosomal recessive metabolic disorder that causes progressive destruction of nerve cells in the brain and spinal cord. It has a similar pathology to Sandhoff disease and Tay-Sachs disease. The three diseases are classified together as the GM2 gangliosidoses, because each disease represents a distinct molecular point of failure in the activation of the same enzyme, beta-hexosaminidase. AB variant is caused by a failure in the gene that makes an enzyme cofactor for beta-hexosaminidase, called the GM2 activator.

Symptoms of beriberi include weight loss, emotional disturbances, impaired sensory perception, weakness and pain in the limbs, and periods of irregular heart rate. Edema (swelling of bodily tissues) is common. It may increase the amount of lactic acid and pyruvic acid within the blood. In advanced cases, the disease may cause high-output cardiac failure and death.

Symptoms may occur concurrently with those of Wernicke's encephalopathy, a primarily neurological thiamine-deficiency related condition.

Beriberi is divided into four categories as follows. The first three are historical and the fourth, gastrointestinal beriberi, was recognized in 2004:

- "Dry beriberi" specially affects the peripheral nervous system

- "Wet beriberi" specially affects the cardiovascular system and other bodily systems

- "Infantile beriberi" affects the babies of malnourished mothers

- "Gastrointestinal beriberi" affects the digestive system and other bodily systems

It is characterized by a deficiency in biliary copper excretion that causes deformations in the skeleton. These include projections on the back of the skull (parasagittal bone exostoses arising from the occipital bone—the so-called "occipital horns") as well as deformities of the elbow, radial head dislocation, hammer-shaped lateral ends of the clavicles, and abnormalities of the hips and pelvis.

OHS presents in early to middle childhood. Children may present with features such as:

Tay–Sachs disease is a genetic disorder that results in the destruction of nerve cells in the brain and spinal cord. The most common type, known as infantile Tay–Sachs disease, becomes apparent around three to six months of age with the baby losing the ability to turn over, sit, or crawl. This is then followed by seizures, hearing loss, and inability to move. Death usually occurs in early childhood. Less commonly the disease may occur in later childhood or adulthood. These forms are generally milder in nature.

Tay–Sachs disease is caused by a genetic mutation in the "HEXA" genes on chromosome 15. It is inherited from a person's parents in an autosomal recessive manner. The mutation results in problems with an enzyme called beta-hexosaminidase A which results in the buildup of the molecule GM2 ganglioside within cells, leading to toxicity. Diagnosis is by measuring the blood hexosaminidase A level or genetic testing. It is a type of sphingolipidoses.

The treatment of Tay–Sachs disease is supportive in nature. This may involve multiple specialities as well as psychosocial support for the family. The disease is rare in the general population. In Ashkenazi Jews, French Canadians of southeastern Quebec, and Cajuns of southern Louisiana, the condition is more common. Approximately 1 in 3,600 Ashkenazi Jews at birth are affected.

The disease is named after Waren Tay, who in 1881 first described a symptomatic red spot on the retina of the eye; and Bernard Sachs, who described in 1887 the cellular changes and noted an increased rate of disease in Ashkenazi Jews. Carriers of a single Tay–Sachs allele are typically normal. It has been hypothesized that being a carrier may confer protection from another condition such as tuberculosis, explaining the persistence of the allele in certain populations. Researchers are looking at gene therapy or enzyme replacement therapy as possible treatments.

Wernicke's encephalopathy (WE), Korsakoff's syndrome (alcohol amnestic disorder), Wernicke–Korsakoff syndrome are forms of dry beriberi.

Wernicke's encephalopathy is the most frequently encountered manifestation of thiamine deficiency in Western society, though it may also occur in patients with impaired nutrition from other causes, such as gastrointestinal disease, those with HIV-AIDS, and with the injudicious administration of parenteral glucose or hyperalimentation without adequate B-vitamin supplementation. This is a striking neuro-psychiatric disorder characterized by paralysis of eye movements, abnormal stance and gait, and markedly deranged mental function.

Korsakoff's syndrome is, in general, considered to occur with deterioration of brain function in patients initially diagnosed with WE. This is an amnestic-confabulatory syndrome characterized by retrograde and anterograde amnesia, impairment of conceptual functions, and decreased spontaneity and initiative.

Alcoholics may have thiamine deficiency because of the following:

- Inadequate nutritional intake: Alcoholics tend to intake less than the recommended amount of thiamine.

- Decreased uptake of thiamine from the GI tract: Active transport of thiamine into enterocytes is disturbed during acute alcohol exposure.

- Liver thiamine stores are reduced due to hepatic steatosis or fibrosis.

- Impaired thiamine utilization: Magnesium, which is required for the binding of thiamine to thiamine-using enzymes within the cell, is also deficient due to chronic alcohol consumption. The inefficient utilization of any thiamine that does reach the cells will further exacerbate the thiamine deficiency.

- Ethanol "per se" inhibits thiamine transport in the gastrointestinal system and blocks phosphorylation of thiamine to its cofactor form (ThDP).

Following improved nutrition and the removal of alcohol consumption, some impairments linked with thiamine deficiency are reversed, in particular poor brain functionality, although in more severe cases, Wernicke–Korsakoff syndrome leaves permanent damage. (See delirium tremens.)

The classic characterization of the group of neurodegenerative, lysosomal storage disorders called the neuronal ceroid lipofuscinoses (NCLs) is through the progressive, permanent loss of motor and psychological ability with a severe intracellular accumulation of lipofuscins, with the United States and northern European populations having slightly higher frequency with an occurrence of 1 in 10,000. There are four classic diagnoses that have received the most attention from researchers and the medical field, differentiated from one another by age of symptomatic onset, duration, early-onset manifestations such as blindness or seizures, and the forms which lipofuscin accumulation takes.

In the early infantile variant of NCL (also called INCL or Santavuori-Haltia), probands appear normal at birth, but early visual loss leading to complete retinal blindness by the age of 2 years is the first indicator of the disease; by 3 years of age a vegetative state is reached and by 4 years isoelectric encephalograms confirm brain death. Late infantile variant usually manifests between 2 and 4 years of age with seizures and deterioration of vision. The maximum age before death for late infantile variant is 10–12 years. Juvenile NCL (JNCL, Batten Disease, or Spielmeyer-Vogt), with a prevalence of 1 in 100,000, usually arises between 4 and 10 years of age; the first symptoms include considerable vision loss due to retinal dystrophy, with seizures, psychological degeneration, and eventual death in the mid- to late-20s or 30s ensuing. Adult variant NCL (ANCL or Kuf’s Disease) is less understood and generally manifests milder symptoms; however, while symptoms typically appear around 30 years of age, death usually occurs ten years later.

All the mutations that have been associated with this disease have been linked to genes involved with the neural synapses metabolism – most commonly with the reuse of vesicle proteins.

Mucolipidosis (ML) is a group of inherited metabolic disorders that affect the body's ability to carry out the normal turnover of various materials within cells.

When originally named, the mucolipidoses derived their name from the similarity in presentation to both mucopolysaccharidoses and sphingolipidoses. A biochemical understanding of these conditions has changed how they are classified. Although four conditions (I, II, III, and IV) have been labeled as mucolipidoses, type I (sialidosis) is now classified as a glycoproteinosis, and type IV (Mucolipidosis type IV) is now classified as a gangliosidosis.

Occipital horn syndrome (OHS), formerly considered a variant of Ehlers-Danlos syndrome, is an X-linked recessive connective tissue disorder. It is caused by a deficiency in the transport of the essential mineral copper, associated with mutations in the ATP7A gene. Only about 2/3 of children with OHS are thought to have genetically inherited the disorder; the other 1/3 do not have the disease in their family history. Since the disorder is X-linked recessive the disease affects more males. This is because they do not have a second X chromosome, unlike females, so essentially are lacking the 'backup' copy with proper function. Females are much more likely to be carriers only. For a female to be affected they must carry two defective X chromosomes, not just one. The disorder is considered a milder variant of Menkes disease.

Neuronal ceroid lipofuscinosis (NCL) is the general name for a family of at least eight genetically separate neurodegenerative disorders that result from excessive accumulation of lipopigments (lipofuscin) in the body's tissues. These lipopigments are made up of fats and proteins. Their name comes from the word stem "lipo-", which is a variation on "lipid" or "fat", and from the term "pigment", used because the substances take on a greenish-yellow color when viewed under an ultraviolet light microscope. These lipofuscin materials build up in neuronal cells and many organs, including the liver, spleen, myocardium, and kidneys.

The diagnosis of ML is based on clinical symptoms, a complete medical history, and certain laboratory tests.

A patient presenting with Hyper IgM syndrome may be affected by simple infectious organisms in exposed regions like the respiratory system. Vaccination against pathogenic organisms may not help these individuals, because vaccinating them does not properly stimulate production of antibodies. Symptoms can include:

- Fever (recurrent infections)

- Low counts of IgA, IgG and IgE antibodies

- CD40L not reactive in T cells

- Recurrent sinopulmonary and GI infections with pyogenic bacteria and opportunistic organisms, and cutaneous manifestations including pyodermas extensive warts.