Symptoms range widely in their onset and severity. The onset of the most severe form, type III, begins within the first months of life and includes a quick progression of intellectual disability, liver and spleen enlargement (splenomegaly), hearing loss, respiratory infections and skeletal abnormalities. Often the appearance of an affected individual includes the following facial features: protruding forehead, leveled nasal bridge, small nose and wide mouth. Muscular weakness or spinal abnormalities can occur due to the buildup of storage materials in the muscle. A milder form of alpha-mannosidosis involves mild to moderate intellectual disability which develops during childhood or adolescence.

Late-onset PFK deficiency, as the name suggests, is a form of the disease that presents later in life. Common symptoms associated with late-onset phosphofructokinase deficiency are myopathy, weakness and fatigue. Many of the more severe symptoms found in the classic type of this disease are absent in the late-onset form.

Patients generally have a benign course, and typically present with hepatomegaly and growth retardation early in childhood. Mild hypoglycemia, hyperlipidemia, and hyperketosis may occur. Lactic acid and uric acid levels may be normal. However, lactic acidosis may occur during fasting.

Phosphofructokinase deficiency also presents in a rare infantile form. Infants with this deficiency often display floppy infant syndrome (hypotonia), arthrogryposis, encephalopathy and cardiomyopathy. The disorder can also manifest itself in the central nervous system, usually in the form of seizures. PFK deficient infants also often have some type of respiratory issue. Survival rate for the infantile form of PFK deficiency is low, and the cause of death is often due to respiratory failure.

Symptoms present by eight months of age and are marked by developmental delay followed by neurological complications such as seizures, involuntary eye movements, and ataxia, involuntary muscle movements and failure to gain weight and grow at the expected rate (failure to thrive). Babies with this condition also have and enlarged liver and spleen (hepatosplenomegaly) and enlarged heart (cardiomegaly).

Type 1 usually begins somewhere in the first three to 18 months of age and in considered the most severe of the three types. Symptoms include:

- Coarse facial features

- Enlarged liver, spleen, and/or heart

- Intellectual disability

- Seizures

- Abnormal bone formation of many bones

- Progressive deterioration of brain and spinal cord

- Increased or decreased perspiration

Patients have no vascular lesions, but have rapid psychomotor regression, severe and rapidly progressing neurologic signs, elevated sodium and chloride excretion in the sweat, and fatal outcome before the sixth year.

Type 2 appears when a child is around 18 months of age and in considered milder than Type 1 but still severe. Symptoms include:

- Symptoms similar to Type 1 but milder and progress more slowly.

The signs and symptoms in glycogen storage disease type IX include:

- Enlarged liver

- Slowed growth

- Motor development delay (mild)

- Low blood sugar accompanied by ketosis

- Lack of muscle tone

Most of these signs and symptoms diminish as adulthood sets in.

A defective alpha-mannosidase enzyme, which normally helps to break down complex sugars derived from glycoproteins in the lysosome, causes sugar build up and impairs cell function. Complete absence of functionality in this enzyme leads to death during early childhood due to deterioration of the central nervous system. Enzymes with low residual activity lead to a milder type of the disease, with symptoms like reduced hearing, mental disabilities, susceptibility to bacterial infections, and skeletal deformities. The course of the disease is progressive.

Alpha-mannosidosis is classified into types I through III based on severity and age of onset. In contrast to the usual classifications scheme of these disorders, type III is the most severe.

Symptoms of early infantile GM1 (the most severe subtype, with onset shortly after birth) may include neurodegeneration, seizures, liver enlargement (hepatomegaly), spleen enlargement (splenomegaly), coarsening of facial features, skeletal irregularities, joint stiffness, distended abdomen, muscle weakness, exaggerated startle response to sound, and problems with gait.

About half of affected patients develop cherry-red spots in the eye.

Children may be deaf and blind by age 1 and often die by age 3 from cardiac complications or pneumonia.

- Autosomal recessive disorder; beta-galactosidase deficiency; neuronal storage of GM1 ganglioside and visceral storage of galactosyl oligosaccharides and keratan sulfate.

- Early psychomotor deterioration: decreased activity and lethargy in the first weeks; never sit; feeding problems - failure to thrive; visual failure (nystagmus noted) by 6 months; initial hypotonia; later spasticity with pyramidal signs; secondary microcephaly develops; decerebrate rigidity by 1 year and death by age 1–2 years (due to pneumonia and respiratory failure); some have hyperacusis.

- Macular cherry-red spots in 50% by 6–10 months; corneal opacities in some

- Facial dysmorphology: frontal bossing, wide nasal bridge, facial edema (puffy eyelids); peripheral edema, epicanthus, long upper lip, microretrognathia, gingival hypertrophy (thick alveolar ridges), macroglossia

- Hepatomegaly by 6 months and splenomegaly later; some have cardiac failure

- Skeletal deformities: flexion contractures noted by 3 months; early subperiosteal bone formation (may be present at birth); diaphyseal widening later; demineralization; thoracolumbar vertebral hypoplasia and beaking at age 3–6 months; kyphoscoliosis. *Dysostosis multiplex (as in the mucopolysaccharidoses)

- 10–80% of peripheral lymphocytes are vacuolated; foamy histiocytes in bone marrow; visceral mucopolysaccharide storage similar to that in Hurler disease; GM1 storage in cerebral gray matter is 10-fold elevated (20–50-fold increased in viscera)

- Galactose-containing oligosacchariduria and moderate keratan sulfaturia

- Morquio disease Type B: Mutations with higher residual beta-galactosidase activity for the GM1 substrate than for keratan sulfate and other galactose-containing oligosaccharides have minimal neurologic involvement but severe dysostosis resembling Morquio disease type A (Mucopolysaccharidosis type 4).

Neutral lipid storage disease (also known as Chanarin–Dorfman syndrome) is an autosomal recessive disorder characterized by accumulation of triglycerides in the cytoplasm of leukocytes, muscle, liver, fibroblasts, and other tissues.

It can be associated with "CGI58".

The symptoms of Sly syndrome are similar to those of Hurler syndrome (MPS I). The symptoms include:

- in the head, neck, and face: coarse (Hurler-like) facies and macrocephaly, frontal prominence, premature closure of sagittal lambdoid sutures, and J-shaped sella turcica

- in the eyes: corneal opacity and iris coloboma

- in the nose: anteverted nostrils and a depressed nostril bridge

- in the mouth and oral areas: prominent alveolar processes and cleft palate

- in the thorax: usually pectus carinatum or exacavatum and oar-shaped ribs; also a protruding abdomen and inguinal or umbilical hernia

- in the extremities: talipes, an underdeveloped ilium, aseptic necrosis of femoral head, and shortness of tubular bones occurs

- in the spine: kyphosis or scoliosis and hook-like deformities in thoracic and lumbar vertebrate

- in the bones: dysostosis multiplex

In addition recurrent pulmonary infections occur. Hepatomegaly occurs in the gastrointestinal system. Splenomegaly occurs in the hematopoietic system. Inborn mucopolysaccharide metabolic disorders due to β-glucuronidase deficiency with granular inclusions in granulocytes occurs in the biochemical and metabolic systems. Growth and motor skills are affected, and mental retardation also occurs.

Glycogen storage disease type III presents during infancy with hypoglycemia and failure to thrive. Clinical examination usually reveals hepatomegaly. Muscular disease, including hypotonia and cardiomyopathy, usually occurs later. The liver pathology typically regresses as the individual enter adolescence, as does splenomegaly, should the individual so develop it.

The onset of this disease is usually noticed in childhood, but often not diagnosed until the third or fourth decade of life. Symptoms include exercise intolerance with muscle pain, early fatigue, painful cramps, and myoglobin in the urine (often provoked by a bout of exercise). Myoglobinuria may result from the breakdown of skeletal muscle known as rhabdomyolysis, a condition in which muscle cells breakdown, sending their contents into the bloodstream.

Patients may exhibit a “second wind” phenomenon. This is characterized by the patient’s better tolerance for aerobic exercise such as walking and cycling after approximately 10 minutes. This is attributed to the combination of increased blood flow and the ability of the body to find alternative sources of energy, like fatty acids and proteins. In the long term, patients may exhibit renal failure due to the myoglobinuria, and with age, patients may exhibit progressively increasing weakness and substantial muscle loss.

Patients may present at emergency rooms with severe fixed contractures of the muscles and often severe pain. These require urgent assessment for rhabdomyolysis as in about 30% of cases this leads to acute renal failure. Left untreated this can be life-threatening. In a small number of cases compartment syndrome has developed, requiring prompt surgical referral.

Onset of late infantile GM1 is typically between ages 1 and 3 years.

Neurological symptoms include ataxia, seizures, dementia, and difficulties with speech.

Infantile free sialic acid storage disease (ISSD) is a lysosomal storage disease Occurs when a sialic acid, is unable to be transported out of the lysosomal membrane and instead, accumulates in the tissue and free sialic acid is excreted in the urine. Mutations in the SLC17A5 (solute carrier family 17 (anion/sugar transporter), member 50) gene cause all forms of sialic acid storage disease. The SLC17A5 gene is located on the long (q) arm of chromosome 6 between positions 14 and 15. This gene provides instructions for producing a protein called sialin that is located mainly on the membranes of lysosomes, compartments in the cell that digest and recycle materials.

ISSD is the most severe form of the sialic acid storage diseases. Babies with this condition have severe developmental delay, weak muscle tone (hypotonia), and failure to gain weight and grow at the expected rate (failure to thrive). They may have unusual facial features that are often described as "coarse," seizures, bone malformations, enlarged liver and spleen (hepatosplenomegaly), and an enlarged heart (cardiomegaly).

ISSD is a rare autosomal recessive disorder and affects 1 in 528,000 live births worldwide.

A prenatal diagnosis was made by Kleijer et al. in 1979 by measuring beta-galactosidase and neuraminidase activities in cultured amniotic fluid cells.

Remarks:

- Some GSDs have different forms, e.g. infantile, juvenile, adult (late-onset).

- Some GSDs have different subtypes, e.g. GSD1a / GSD1b, GSD9A1 / GSD9A2 / GSD9B / GSD9C / GSD9D.

- GSD type 0: Although glycogen synthase deficiency does not result in storage of extra glycogen in the liver, it is often classified with the GSDs as type 0 because it is another defect of glycogen storage and can cause similar problems.

- GSD type VIII (GSD 8): In the past it was considered a distinct condition, however it is now classified with GSD type VI or GSD IXa1; it has been described as X-linked recessive inherited.

- GSD type XI (GSD 11): Fanconi-Bickel syndrome, hepatorenal glycogenosis with renal Fanconi syndrome, no longer considered a glycogen storage disease.

- GSD type XIV (GSD 14): Now classed as Congenital disorder of glycosylation type 1 (CDG1T), affects the phosphoglucomutase enzyme (gene PGM1).

- Lafora disease is considered a complex neurodegenerative disease and also a glycogen metabolism disorder.

Glycogen storage disease type VI (GSD VI) is a type of glycogen storage disease caused by a deficiency in liver glycogen phosphorylase or other components of the associated phosphorylase cascade system. It is also known as "Hers' disease", after Henri G. Hers, who characterized it in 1959. The scope of GSD VI now also includes glycogen storage disease type VIII, IX (caused by phosphorylase b kinase deficiency) and X (deficiency protein kinase A).

The incidence of GSD VI is approximately 1 case per 65,000–85,000 births, representing approximately 30% all cases of glycogen storage disease. Approximately 75% of these GSD VI cases result from the X-linked recessive forms of phosphorylase kinase deficiency, all other forms are autosomal recessive.

Sly syndrome, also called mucopolysaccharidosis type VII (MPS 7), is an autosomal recessive lysosomal storage disease characterized by a deficiency of the enzyme β-glucuronidase, a lysosomal enzyme. Sly syndrome belongs to a group of disorders known as mucopolysaccharidoses, which are lysosomal storage diseases. In Sly syndrome, the deficiency in β-glucuronidase leads to the accumulation of certain complex carbohydrates (mucopolysaccharides) in many tissues and organs of the body.

It was named after its discoverer William S. Sly, an American biochemist who has spent nearly his entire academic career at Saint Louis University.

Glycogen storage disease type XI is a form of glycogen storage disease. It is also known as "Fanconi–Bickel syndrome", for Guido Fanconi and Horst Bickel, who first described it in 1949.

It is associated with GLUT2, a glucose transport protein which, when functioning normally, allows glucose to exit several tissues, including the liver, nephrons, and enterocytes of the intestines, and enter the blood. The syndrome results in hepatomegaly secondary to glycogen accumulation, glucose and galactose intolerance, fasting hypoglycaemia, a characteristic proximal tubular nephropathy and severe short stature.

Glycogen storage disease type IX is a hereditary deficiency of glycogen phosphorylase kinase B that affects the liver and skeletal muscle tissue. It is inherited in an X-linked or autosomal recessive manner.

Glycogen storage disease type V (GSD-V) is a metabolic disorder, more specifically a glycogen storage disease, caused by a deficiency of myophosphorylase. Its incidence is reported as 1 in 100,000, approximately the same as glycogen storage disease type I.

The disease was first reported in 1951 by Dr. Brian McArdle of Guy's Hospital, London.

Numerous genetic disorders are caused by errors in fatty acid metabolism. These disorders may be described as fatty oxidation disorders or as a "lipid storage disorders", and are any one of several inborn errors of metabolism that result from enzyme defects affecting the ability of the body to oxidize fatty acids in order to produce energy within muscles, liver, and other cell types.

Some of the more common fatty acid metabolism disorders are:

Galactosialidosis is a lysosomal storage disease.This condition is rare and most cases have been in the juvenile/adult group of patients. An infantile form has been described.