Metabolic
Acute Intermittent Porphyria (AIP)
Overview
AIP is one of a group of blood conditions, known as porphyrias, that result from a lack of activity from a specific enzyme the body needs to produce heme. This causes a build-up of intermediate products (unfinished heme) which is thought to cause the characteristic and life-threatening symptoms of AIP. These symptoms include severe abdominal pain, vomiting, constipation, diarrhea, red or dark-colored urine, muscle weakness, breathing problems, fast heart rate, hypertension (high blood pressure), convulsions, psychological symptoms (such as minor behavioral changes, anxiety, confusion, or depression), and pain in the arms, hands, legs, feet, back, chest, neck, or head.
Homocystinuria
Overview
Homocystinuria is the term used for several rare genetic disorders (diseases passed down through families) that cause levels of homocysteine to build up in blood and urine. This build-up primarily occurs when the body cannot properly process methionine. Methionine and homocysteine are two very important amino acids. Amino acids are the building blocks that the body uses to make proteins. There are multiple forms of homocystinuria, which are distinguished by their signs and symptoms and genetic causes. High levels of homocysteine and abnormal levels of methionine can cause many different symptoms in the body and lead to chronic, serious, and potentially life-threatening health issues.
Hyperammonemia
Overview
Hyperammonemia, a metabolic condition characterized by excess ammonia in the blood, can be life-threatening and may affect patients at any age. Clinical signs and symptoms of hyperammonemia are typically neurological in origin, but they can be generally nonspecific and may suggest several diagnostic pathways. The clinical presentation of neonatal hyperammonemia, which can mimic sepsis, includes nonspecific symptoms that are mainly neurological in origin. Hyperammonemia in infants (beyond neonates), children, and adults may be more episodic, difficult to recognize and precipitated by catabolic events, protein overload or certain drugs. The causes of hyperammonemia are diverse. Some of the more common causes include liver disease, reactions to drugs, hemolytic disease, or gastrointestinal bleeds and urea cycle disorders (UCDs) or other inborn errors of metabolism (IEMs).
Ocular Manifestations of Cystinosis
Overview
Cystinosis is a rare genetic disorder affecting multiple organs and systems that most frequently begins in infancy. Cystinosis is estimated to affect 1 in every 100,000 – 200,000 live births each year. Cystinosis is caused by a mutation in the CTNS gene that results in impaired transport of the cystine out of lysosomes in cells. This, in turn, leads to the formation and accumulation of cystine crystals in cells, causing damage to organs throughout the body and significant impact on the eyes. Systemic treatment is not effective in the cornea, as it is avascular, and must be treated separately.
The cornea, or front layer of the eye, is the part of the eye that may be most affected.
The first and most frequently reported ocular symptom is photophobia — sensitivity to light that results in discomfort. It is thought that photophobia is mainly due to the presence of corneal cystine crystals that cause light entering the eye to scatter. As the disease progresses, ocular symptoms increase in number and intensity, daily activities become more difficult to carry out, and severe complications may develop, including visual impairment and potential corneal transplant.
