Introduction
Lattice corneal dystrophy type II is identified by the buildup of protein clumps known as amyloid deposits in various tissues across the body. These deposits commonly form in the walls of blood vessels and basement membranes, which are structures that provide support to cells in different tissues. The presence of amyloid deposits contributes to specific symptoms affecting the eyes, nerves, and skin, which tend to deteriorate as a person ages.
What Is Lattice Corneal Dystrophy (LCD)?
Lattice Corneal Dystrophy (LCD) is a rare genetic disorder that impacts the cornea, the clear front part of the eye. It is characterized by the buildup of an abnormal protein (amyloid) in the stromal layer of the cornea, forming a distinct lattice-like pattern. This leads to gradual thinning and eventual loss of a layer called the Bowman layer. The condition usually affects both eyes and primarily impacts central vision, leaving peripheral vision unaffected. LCD can be classified into different types, each with specific clinical features and varying severity. Symptoms typically start in childhood and commonly include eye irritation, sensitivity to light, and progressive vision loss, with visible lattice-like lines in the cornea when viewed from behind the eye.
What Are the Symptoms of Lattice Corneal Dystrophy Type II?
The initial indication of lattice corneal dystrophy type II, often detected in a person's twenties, is the buildup of amyloid deposits in the cornea. The cornea, the eye's transparent outer layer, comprises multiple tissue layers. In this type of dystrophy, the amyloid deposits form within the stromal layer, creating a lattice-like pattern with delicate, branching fibers. These deposits cloud the cornea, leading to vision impairment and recurrent corneal erosions, which are intensely painful and can cause sensitivity to bright light (photophobia). Both eyes are usually affected.
As lattice corneal dystrophy type II advances, typically around a person's forties, nerve involvement becomes evident. Amyloid deposits are believed to disrupt nerve function, particularly affecting cranial nerves. This can result in facial muscle paralysis (facial palsy), reduced facial sensation (facial hypoesthesia), and difficulties with speech, chewing, and swallowing. Peripheral nerves, connecting the brain and spinal cord to muscles and sensory cells, may also be affected, leading to peripheral neuropathy characterized by loss of sensation, weakness, and clumsiness, primarily in the lower limbs and arms.
Skin manifestations commonly appear around the forties as well. These include thickened, sagging skin, particularly on the scalp and forehead, and a condition called cutis laxa, characterized by loose, inelastic skin. Dry, itchy skin is also common. Due to muscle paralysis and loose skin, individuals may exhibit a sad facial expression.
What Is the Cause of Lattice Corneal Dystrophy Type II?
Lattice corneal dystrophy type II arises from mutations within the GSN gene, which encodes the gelsolin protein. Gelsolin plays a crucial role across the body by regulating the formation of protein filaments that provide structure to cells (known as the cytoskeleton). In this condition, mutations alter a single building block (amino acid) within the gelsolin protein. Consequently, the mutated gelsolin protein is processed differently from its normal counterpart, forming abnormal protein fragments. These fragments aggregate and form amyloid deposits, contributing to the characteristic signs and symptoms of lattice corneal dystrophy type II.
Is Lattice Corneal Dystrophy Type II Inherited?
This condition follows an autosomal dominant inheritance pattern, indicating that having just one copy of the altered gene in each cell adequately triggers the disorder. While a mutation in only one copy of the gene can lead to the disorder, individuals with mutations in both copies tend to experience more pronounced signs and symptoms.
Autosomal dominant inheritance means that a single mutated copy of the gene, inherited from one parent, is enough to cause the condition. However, if both copies of the gene, one from each parent, are mutated, the symptoms may be more severe. This explains why some individuals may have milder symptoms if they inherit only one mutated copy of the gene, while those with mutations in both copies may experience more significant effects of the disorder.
What Is the Diagnosis of Lattice Corneal Dystrophy Type II?
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Comprehensive Eye Examination: Diagnosis of lattice corneal dystrophy type II (LCDII) typically begins with a thorough eye examination conducted by an ophthalmologist or optometrist. This examination may include assessments of visual acuity, intraocular pressure, and examination of the anterior segment of the eye.
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Slit-Lamp Examination: A slit-lamp examination is a specialized tool used to examine the structures of the eye under high magnification and intense illumination. This allows the healthcare provider to visualize any abnormalities in the cornea, including the presence of characteristic lattice-like deposits.
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Corneal Imaging Techniques: Various corneal imaging techniques may be employed to assess the extent of corneal involvement and abnormal protein deposits. Optical coherence tomography (OCT) and confocal microscopy are commonly used imaging modalities that provide detailed cross-sectional images of the cornea.
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Genetic Testing: Genetic testing may be recommended to confirm the diagnosis of LCDII, particularly in cases with uncertainty or a family history of the condition. Testing typically involves sequencing the TGFBI gene to identify any mutations associated with the disorder.
What Is the Treatment of Lattice Corneal Dystrophy Type II?
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Artificial Tears and Lubricating Eye Drops: Lubricating eye drops, also known as artificial tears, can help alleviate symptoms of dryness and discomfort associated with LCDII. These drops help moisten the ocular surface and reduce irritation caused by abnormal protein deposits.
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Bandage Contact Lenses: Soft or bandage contact lenses may be prescribed to protect the cornea and promote the healing of recurrent corneal erosions. These lenses create a smooth surface over the cornea, reducing friction and preventing further damage.
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Phototherapeutic Keratectomy (PTK): Phototherapeutic keratectomy is a surgical procedure that uses a laser to remove abnormal protein deposits from the cornea. This procedure helps improve vision and reduce symptoms by smoothing the corneal surface. PTK may be recommended for individuals with significant visual impairment or recurrent corneal erosions that do not respond to other treatments.
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Corneal Transplantation (Penetrating Keratoplasty): In advanced cases of LCDII where vision is severely compromised, and other treatment options have been exhausted, a corneal transplant may be necessary. During a corneal transplant, the damaged cornea is replaced with a healthy donor cornea obtained from a deceased donor. This procedure can significantly improve vision and alleviate symptoms, although there is a risk of rejection and other complications.
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Genetic Counseling: Genetic counseling may be beneficial for individuals with LCDII and their families. It can help them understand the inheritance pattern of the condition and make informed decisions about family planning. A genetic counselor can inform future generations about the genetic risk of passing the condition and discuss available testing options.
Conclusion
Lattice Corneal Dystrophy Type II (LCDII) is a rare genetic disorder characterized by amyloid deposits in the cornea. These deposits lead to vision impairment and various systemic manifestations affecting nerves and skin. Mutations in the GSN gene are responsible for this condition, which follows an autosomal dominant inheritance pattern. Diagnosis typically involves comprehensive eye examinations, corneal imaging, and genetic testing. Treatment options include artificial tears, bandage contact lenses, phototherapeutic keratectomy, corneal transplantation, and genetic counseling.
