Familial amyloidosis, Finnish type

Other Names: Amyloidosis, Meretoja type; Amyloid cranial neuropathy with lattice corneal dystrophy; Amyloidosis V; Lattice corneal dystrophy type II Finnish; Familial amyloid polyneuropathy type IV; Hereditary gelsolin amyloidosis; AGel amyloidosis

Familial amyloidosis, Finnish type, or gelsolin amyloidosis, is a condition characterized by abnormal deposits of amyloid protein that mainly affect the eyes, nerves and skin. The 3 main features are amyloid deposits in the cornea (corneal lattice dystrophy), bilateral facial paralysis, and cutis laxa ("sagging" skin). The deposits frequently occur in blood vessel walls and basement membranes, which are thin, sheet-like structures that separate and support cells in many tissues. Amyloid deposits lead to characteristic signs and symptoms involving the eyes, nerves, and skin that worsen with age.

Epidemiology

Lattice corneal dystrophy type II is a rare condition; however, the prevalence is unknown. While this condition can be found in populations worldwide, it was first described in Finland and is more common there.

Cause

Lattice corneal dystrophy type II is caused by mutations in the GSN gene. This gene provides instructions for making a protein called gelsolin. This protein is found throughout the body and helps regulate the formation of the network of protein filaments that gives structure to cells (the cytoskeleton). Mutations that cause lattice corneal dystrophy type II change a single protein building block (amino acid) in the gelsolin protein. The altered gelsolin protein is broken down differently than the normal protein, which results in an abnormal gelsolin protein fragment that is released from the cell. These protein fragments clump together and form amyloid deposits, which lead to the signs and symptoms of lattice corneal dystrophy type II.

Inheritance

Autosomal dominant pattern, a 50/50 chance.

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Although a mutation in one copy of the gene can cause the disorder, people with mutations in both copies of the gene have more severe signs and symptoms.

Signs and symptoms

Symptoms of this condition usually begin in an individual's 20s or 30s, and they usually emerge in a specific order. The progression is often slow, but varies among individuals. The typical triad of features includes accumulation of amyloid deposits in the cornea (lattice corneal dystrophy), cutis laxa (sagging skin), and nervous system symptoms (neuropathy).

Eye symptoms typically begin first. The amyloid deposits cloud the cornea, often leading to vision impairment. Other eye symptoms may include dryness, irritation and light sensitivity. Affected individuals may eventually develop cataracts and glaucoma.

As the condition progresses, the nerves become involved (typically in an individual's 40s). Dysfunction of the nerves in the head and face (cranial nerves) causes paralysis of facial muscles and decreased sensation, which can lead to difficulty speaking, chewing, and swallowing. Facial paralysis can also cause additional eye symptoms including ectropium (turning out of the eyelid), corneal ulcers, or droopy eyelids (ptosis). Affected individuals may also have peripheral neuropathy. Central nervous system symptoms such as impaired cognitive function are rare but have been reported in older individuals.

Skin manifestations may also begin in a person's 40s and include a thickened, sagging appearance and cutis laxa (loose skin that lacks elasticity), especially on the face. Cutis laxa worsens with age.

Other signs and symptoms that have been reported in some people include gastric motility changes, orodental problems, heart palpitations, cardiac conduction problems, and mild proteinuria.

NIH genetic and rare disease info

• NIH info on Familial amyloidosis, Finnish type

Familial amyloidosis, Finnish type is a rare disease.

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