Lamellar ichthyosis is a condition that mainly affects the skin. Infants with this condition are typically born with a tight, clear sheath covering their skin called a collodion membrane. This membrane usually dries and peels off during the first few weeks of life, and then it becomes obvious that affected babies have scaly skin, and eyelids and lips that are turned outward. People with lamellar ichthyosis typically have large, dark, plate-like scales covering their skin on most of their body. Infants with lamellar ichthyosis may develop infections, an excessive loss of fluids (dehydration), and respiratory problems. Affected individuals may also have hair loss (alopecia), abnormally formed fingernails and toenails (nail dystrophy), a decreased ability to sweat (hypohidrosis), an increased sensitivity to heat, and a thickening of the skin on the palms of the hands and soles of the feet (keratoderma). Less frequently, affected individuals have reddened skin (erythema) and joint deformities (contractures).

Lamellar ichthyosis is estimated to affect 1 in 100,000 individuals in the United States. This condition is more common in Norway, where an estimated 1 in 91,000 individuals are affected.

Mutations in one of many genes can cause lamellar ichthyosis. These genes provide instructions for making proteins that are found in the outermost layer of the skin (the epidermis). The skin abnormalities associated with lamellar ichthyosis disrupt the normal formation of the epidermis, resulting in impaired regulation of body temperature, water retention, and resistance to infections.

Mutations in the TGM1 gene are responsible for approximately 90 percent of cases of lamellar ichthyosis. The TGM1 gene provides instructions for making an enzyme called transglutaminase 1. This enzyme is involved in the formation of the cornified cell envelope, which is a structure that surrounds skin cells and helps form a protective barrier between the body and its environment. TGM1 gene mutations lead to severely reduced or absent enzyme production, which prevents the formation of the cornified cell envelope.

Mutations in other genes associated with lamellar ichthyosis are each responsible for only a small percentage of cases. In some people with lamellar ichthyosis, the cause of the disorder is unknown. Researchers have identified multiple chromosome regions that contain genes that may be associated with lamellar ichthyosis, although the specific genes have not been identified.

Normal Function

The ABCA12 gene provides instructions for making a protein known as an ATP-binding cassette (ABC) transporter. ABC transporter proteins carry many types of molecules across cell membranes. In particular, the ABCA12 protein plays a major role in transporting fats (lipids) and enzymes in cells that make up the outermost layer of skin (the epidermis). This transport of molecules is needed to maintain the layers of lipids within the epidermis that are necessary to prevent water loss (dehydration) and for normal development of the skin.

Health Conditions Related to Genetic Changes

Harlequin ichthyosis

Many variants (also known as mutations) in the ABCA12 gene have been identified in people with harlequin ichthyosis. This skin condition is characterized by hard, thick scales that are present at birth; excessive dehydration; and increased risk of infections.

Most ABCA12 gene variants result in the production of an abnormally short protein that cannot transport lipids properly. Individuals with ABCA12 gene variants that result in a complete absense of ABCA12 protein often have the most severe skin problems and tend not to survive past infancy. In people with abnormal or nonfunctional ABCA12 protein, a lack of lipid transport causes numerous problems with the development of the epidermis before and after birth. Specifically, it prevents the skin from forming an effective barrier, and leads to the skin problems characteristic of harlequin ichthyosis.

Nonbullous congenital ichthyosiform erythroderma

Variants in the ABCA12 gene have been found to cause nonbullous congenital ichthyosiform erythroderma (NBCIE). This condition affects the skin and causes redness; the development of fine, white scales; an increased risk of infections; and dehydration. These skin abnormalities tend to be less severe than those in harlequin ichthyosis (described above).

Most of the variants that cause NBCIE change single protein building blocks (amino acids) in the ABCA12 protein. These variants likely lead to the production of a protein with reduced function, which impairs lipid transport and the formation of the lipid layers within the epidermis. Problems with this protective barrier underlie the skin abnormalities and other features of NBCIE.

Lamellar ichthyosis

MedlinePlus Genetics provides information about Lamellar ichthyosis

Other Names for This Gene

• ABCAC_HUMAN
• ATP-binding cassette 12
• ATP-binding cassette transporter 12
• ATP-binding cassette, sub-family A (ABC1), member 12
• ATP-binding cassette, sub-family A, member 12
• ICR2B

Genomic Location

Normal Function

The TGM1 gene provides instructions for making an enzyme called transglutaminase 1. This enzyme is found in cells that make up the outermost layer of the skin (the epidermis). Transglutaminase 1 is involved in the formation of the cornified cell envelope, which is a structure that surrounds skin cells and helps form a protective barrier between the body and its environment. Specifically, transglutaminase 1 forms strong bonds, called cross-links, between the structural proteins that make up the cornified cell envelope. This cross-linking provides strength and stability to the epidermis.

Health Conditions Related to Genetic Changes

Lamellar ichthyosis

Many mutations in the TGM1 gene have been found to cause lamellar ichthyosis, which is a condition that causes scaly skin that covers much of the body, and other skin abnormalities. Some TGM1 gene mutations that cause this condition change single DNA building blocks (nucleotides) in the transglutaminase 1 enzyme. The most frequently occurring mutation (written as 877-2A>G) affects the way the gene's instructions are pieced together to form the enzyme and results in an abnormally shortened, nonfunctional enzyme. Other TGM1 gene mutations result in a transglutaminase 1 enzyme that cannot function normally, is abnormally short, or is not produced. A lack of functional transglutaminase 1 prevents the formation of the cornified cell envelope, causing the skin abnormalities of lamellar ichthyosis.

Other disorders

In addition to lamellar ichthyosis (described above), TGM1 gene mutations have been found to cause other forms of ichthyosis. In one type, called self-healing collodion baby, affected infants are born with a tight, clear sheath covering their skin called a collodion membrane. This membrane usually dries and peels off during the first few weeks of life, and affected infants often show near normal skin within a few months. Another type of ichthyosis, called bathing suit ichthyosis, is characterized by scaly skin that is limited to the trunk.

Other Names for This Gene

• epidermal TGase
• ICR2
• protein-glutamine gamma-glutamyltransferase K
• TGASE
• TGase K
• TGase-1
• TGK
• TGM1_HUMAN
• transglutaminase 1 (K polypeptide epidermal type I, protein-glutamine-gamma-glutamyltransferase)
• transglutaminase K
• transglutaminase, keratinocyte
• transglutaminase-1

Genomic Location

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Unfortunately, there is currently no cure for lamellar ichthyosis. Management is generally supportive and based on the signs and symptoms present in each person. For infants, providing a moist environment in an isolette (incubator) and preventing infection are most important. Petrolatum-based creams and ointments are used to keep the skin soft, supple, and hydrated. As affected children become older, treatments to promote peeling and thinning of the stratum corneum (the outermost layer of skin cells) are often recommended. This may include humidification with long baths, lubrication, and keratolytic agents such as alpha-hydroxy acid or urea preparations.

For people with ectropion (turning out of the eyelid), lubrication of the cornea with artificial tears or prescription ointments is helpful to prevent the cornea from drying out. Topical or oral retinoid therapy may be recommended for those with severe skin involvement; however, these medications can be associated with undesired side effects and are, therefore, generally prescribed with caution.