Individuals with Salla disease may present with nystagmus in the first months of life as well as hypotonia, reduced muscle tone and strength, and cognitive impairment. The most severely impaired children do not walk or acquire language, but the typical patient learns to walk and speak and has normal life expectancy. The MRI shows arrested or delayed myelination.

Salla disease (SD), also called sialic acid storage disease or Finnish type sialuria, is an autosomal recessive lysosomal storage disease characterized by early physical impairment and mental retardation. It was first described in 1979, after Salla, a municipality in Finnish Lapland. Salla disease is one of 40 Finnish heritage diseases and affects approximately 130 individuals, mainly from Finland and Sweden.

Kufs is a neuronal disease, meaning it affects the nervous system, specifically voluntary movement and intellectual function. Symptoms of Kufs can manifest anytime between adolescence and adulthood, however it usually appears around age 30.

There are two types of Kufs: Type A and Type B. Type A causes seizures, myoclonic epilepsy (muscle jerks), dementia, ataxia (compromised muscle coordination), tremors and tics, dysarthria (speech difficulties), confusion, and psychotic behaviour. Although similar to Type A, patients with Type B do not suffer from myoclonic epilepsy or dysarthria, and they do display changes in personality. It is occasional that patients present with skin disorders causing dryness, roughness, and scaliness. The skin symptoms specifically, are a result of Keratin buildup in the skin cells (see ‘Genetic Causes’ for more information). Regardless of the type, most Kufs patients do not survive more than 15 years after their symptoms have manifested.

Symptoms are related to the organs in which sphingomyelin accumulates. Enlargement of the liver and spleen (hepatosplenomegaly) may cause reduced appetite, abdominal distension, and pain. Enlargement of the spleen (splenomegaly) may also cause low levels of platelets in the blood (thrombocytopenia).

Accumulation of sphingomyelin in the central nervous system (including the cerebellum) results in unsteady gait (ataxia), slurring of speech (dysarthria), and difficulty in swallowing (dysphagia). Basal ganglia dysfunction causes abnormal posturing of the limbs, trunk, and face (dystonia). Upper brainstem disease results in impaired voluntary rapid eye movements (supranuclear gaze palsy). More widespread disease involving the cerebral cortex and subcortical structures causes gradual loss of intellectual abilities, causing dementia and seizures.

Bones also may be affected: symptoms may include enlarged bone marrow cavities, thinned cortical bone, or a distortion of the hip bone called coxa vara. Sleep-related disorders, such as sleep inversion, sleepiness during the day and wakefulness at night, may occur. Gelastic cataplexy, the sudden loss of muscle tone when the affected patient laughs, is also seen.

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.

Kufs disease is one of many diseases categorized under a disorder known as neuronal ceroid lipofuscinosis (NCLs). NCLs are broadly described to create problems with vision, movement and cognitive function. Among all NCLs diseases, Kufs is the only one that does not affect vision, and although this is a distinguishing factor of Kufs, NCLs are typically differentiated by the age at which they appear in a patient

The development of children born with INCL is normal for the first 8–18 months, but will then flounder and start to regress both physically and mentally. Motor skills and speech are lost, and optic atrophy causes blindness. A variety of neurological symptoms, such as epilepsy and myoclonic seizures, appear. The senses of hearing and touch remain unaffected. The average lifespan of an INCL child is 9–11 years.

Niemann–Pick disease ( ) is a group of inherited, severe metabolic disorders in which sphingomyelin accumulates in lysosomes in cells. The lysosomes normally transport material through and out of the cell.

This disease involves dysfunctional metabolism of sphingolipids, which are fats found in cell membranes, so it is a kind of sphingolipidosis. Sphingolipidoses, in turn, are included in the larger family of lysosomal storage diseases.

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.

At birth, there is no sign that a child will develop symptoms of aspartylglucosaminuria. Typically, signs and symptoms become apparent between two and four years of age and become progressively worse as the individual ages. The following signs and symptoms may appear:

- Individuals are more prone to respiratory infections

- Development of scoliosis

- Seizures or difficulty with movement

- Skin and joints may become loose

- Facial features change progressively; this may include:

- Progression of developmental and mental disabilities, including:

- An intellectual peak occurs in the mid-teens and allows a plateau for the disease. Once an individual hits the age of 25-30 the decrease begins again, including:

(Children are physically uncoordinated, but remain able to play sports and do everyday activities until they reach adulthood.)

- During the first year of life inguinal and umbilical hernias are common.

- Less severe symptoms include:

- People with aspartylglucosaminuria may have lower than average height, because they tend to go through puberty earlier.

- Epilepsy may develop in adulthood.

- Finnish studies have shown that life expectancy is shorter than average.

Infantile neuronal ceroid lipofuscinoses (INCL) or Santavuori disease or Hagberg-Santavuori disease or Santavuori-Haltia disease or Infantile Finnish type neuronal ceroid lipofuscinosis or Balkan disease is a form of NCL and inherited as a recessive autosomal genetic trait. The disorder is progressive, degenerative and fatal, extremely rare worldwide – with approximately 60 official cases reported by 1982, perhaps 100 sufferers in total today – but relatively common in Finland due to the local founder effect.

Niemann–Pick Type B involves an enlarged liver and spleen hepatosplenomegaly, growth retardation, and problems with lung function including frequent lung infections. Other signs include blood abnormalities such as abnormal cholesterol and lipid levels, and low numbers of blood cells involved in clotting (platelets). The brain is not affected in Type B and the disease often presents in the pre-teen years.

Type I citrullinemia (, also known as classic citrullinemia) usually becomes evident in the first few days of life. Affected infants typically appear normal at birth, but as ammonia builds up in the body, they develop a lack of energy (lethargy), poor feeding, vomiting, seizures, and loss of consciousness. These medical problems can be life-threatening in many cases. A milder form of type I citrullinemia is less common in childhood or adulthood. Some people with gene mutations that cause type I citrullinemia never experience signs and symptoms of the disorder.

Type I citrullinemia is the most common form of the disorder, affecting about one in 57,000 births worldwide. Mutations in the "ASS" gene cause type I citrullinemia. The enzyme made by this gene, argininosuccinate synthetase (), is responsible for one step of the urea cycle. Mutations in the "ASS" gene reduce the activity of the enzyme, which disrupts the urea cycle and prevents the body from processing nitrogen effectively. Excess nitrogen, in the form of ammonia, and other byproducts of the urea cycle, accumulate in the bloodstream, leading to the characteristic features of type I citrullinemia.

Citrullinemia is an autosomal recessive urea cycle disorder that causes ammonia and other toxic substances to accumulate in the blood. Since the substances also accumulate in the urine, the disorder can also be called citrullinuria.

Two forms of citrullinemia have been described, both having different signs and symptoms, and are caused by mutations in different genes. Citrullinemia belongs to a class of genetic diseases called urea cycle disorders. The urea cycle is a sequence of chemical reactions taking place in the liver. These reactions process excess nitrogen, generated when protein is used for energy by the body, to make urea, which is excreted by the kidneys.

GRACILE syndrome is a very rare autosomal recessive genetic disorder, one of the Finnish heritage diseases. It is caused by mutation in BCS1L gene that occurs in at least 1 out of 47,000 live births in Finnish people.

GRACILE is an acronym for growth retardation, amino aciduria (amino acids in the urine), cholestasis, iron overload, lactic acidosis, and early death. Other names for this syndrome include Finnish lethal neonatal metabolic syndrome (FLNMS); lactic acidosis, Finnish, with hepatic hemosiderosis; and Fellman syndrome.

One Finnish study which followed 25 cases from 18 families found that half the infants died within 3 days of birth and the other half died before 4 months of age.

Aspartylglucosaminuria (AGU) is an inherited disease that is characterized by a decline in mental functioning, accompanied by an increase in skin, bone and joint issues.

The disease is caused by a defect in an enzyme known as aspartylglucosaminidase. This enzyme plays a significant role in our bodies because it aids in breaking down certain sugars (for example, oligosaccharides) that are attached to specific proteins (for example, glycoproteins). Aspartylglucosaminuria itself is characterized as a lysosomal disease because it does deal with inadequate activity in an enzyme's function. Aspartylglucosaminidase functions to break down glycoproteins. These proteins are most abundant in the tissues of the body and in the surfaces of major organs, such as the liver, spleen, thyroid and nerves. When glycoproteins are not broken down, aspartylglucosaminidase backs up in the lysosomes along with other substances. This backup causes progressive damage to the tissues and organs.

CCD causes persistent secretory diarrhea. In a fetus, it leads to polyhydramnios and premature birth. Immediately after birth, it leads to dehydration, hypoelectrolytemia, hyperbilirubinemia, abdominal distention, and failure to thrive.

Niemann–Pick disease, SMPD1-associated refers to two different types of Niemann–Pick disease which are associated with the SMPD1 gene.

There are approximately 1,200 cases of NPA and NPB worldwide with the majority of cases being Type B or an intermediate form.

Descriptions of type E and type F have been published, but they are not well characterized, and are currently classified under type B.

Northern epilepsy syndrome or progressive epilepsy with mental retardation (EPMR) is a subtype of neuronal ceroid lipofuscinosis and a rare disease that is regarded as a Finnish heritage disease. Unlike most Finnish heritage diseases, this syndrome has been reported only in Finland.

The disease is characterized by seizures in early childhood that progressively get worse until after puberty. Once the onset of seizures occurs, mental degradation is seen. This continues into adulthood even after seizure frequency has decreased. The cause of the disease is a missense mutation in chromosome 8. The creation of a new protein occurs and the lipid content of the brain is altered because of it. The ratio of the mutation carriers is 1:135. There is nothing that has been found to stop the progression of the disease, but symptomatic approaches, such as the use of benzodiazepines, have helped control seizures.

Hereditary gelsolin amyloidosis is a cutaneous condition inherited in an autosomal dominant fashion.

The condition was first described in 1969, by the Finnish ophthalmologist Jouko Meretoja, and is also known as Familial amyloid neuropathy type IV, Meretoja syndrome, Hereditary amyloidosis, Finnish type.

The disorder primarily associated with eye, skin and cranial nerve symptoms. It is a form of amyloidosis, where the amyloid complexes are formed from fragments of the protein gelsolin in the plasma, due to a mutation in the GSN gene (c.654G>A or c.654G>T).

Northern Epilepsy Syndrome causes recurrent seizures between the ages of five to ten. These seizures, that may last up to 15 minutes, can be classified mostly as tonic-clonic, but partial seizures could also occur. The seizures commonly involve muscle rigidity, convulsions, and loss of consciousness. Generally, the recurrence is one to two times per month.

In the years following the onset of seizures, a noticeable decrease in intellectual capacity is observed.

Sialuria is a condition where there is increased sialic acid in the urine.

Types include:

- Salla disease ("Finnish type sialuria")

- "French type sialuria" (), associated with "GNE"

Lysinuric protein intolerance (LPI), also called hyperdibasic aminoaciduria type 2,cationic aminoaciduria or familial protein intolerance, is an autosomal recessive metabolic disorder affecting amino acid transport.

About 140 patients have been reported, almost half of them of Finnish origin. Individuals from Japan, Italy, Morocco and North Africa have also been reported.

Congenital chloride diarrhea (CCD, also congenital chloridorrhea or Darrow Gamble syndrome) is a genetic disorder due to an autosomal recessive mutation on chromosome 7. The mutation is in downregulated-in-adenoma (DRA), a gene that encodes a membrane protein of intestinal cells. The protein belongs to the solute carrier 26 family of membrane transport proteins. More than 20 mutations in the gene are known to date. A rare disease, CCD occurs in all parts of the world but is more common in some populations with genetic founder effects, most notably in Finland.