In addition, sitosterolemia patients may develop hemolytic episodes and splenomegaly. Untreated, the condition causes a significant increase in morbidity and mortality. Coronary heart disease and its inherent health consequences are the primary causes of illness and premature death in untreated patients. Pathogenesis
Mammalian cells cannot use plant sterols. Normally, plant sterols are poorly absorbed from the gastrointestinal tract; fewer than 5% of plant sterols are absorbed compared to approximately 40% of cholesterol absorbed. The liver preferentially excretes plant sterols over cholesterol. Dietary sterols have recently been shown to passively enter intestinal cells, and subsequently the vast majority are pumped back into the gut lumen by ATP-binding cassette transporter (ABC transporter) proteins. Sitosterolemia is inherited as a rare autosomal recessive condition. It has been shown to result from mutations in either of  two adjacent and oppositely oriented genes (ABCG5 and ABCG8) located in chromosome 2 in band 2p21 and encode for  ABC transporter proteins named sterolin-1 and sterolin-2, respectively. Thus, the active pumping back into the intestine of passively absorbed plant sterols is disrupted, and hepatic secretion of the resultant accumulation of these sterols is decreased. The ability of the liver to preferentially excrete plant sterols into the bile is apparently impaired. While bile acid synthesis remains the same as in healthy people, the total excretion of sterols in the bile is reportedly less than 50% in subjects with sitosterolemia compared to control subjects. The mechanism for decreased hepatic secretion is unknown.
Conductive hearing loss developing during childhood is usually due to otitis media with effusion and may present with speech and language delay or difficulty hearing. Later onset of conductive hearing loss may have an obvious cause such as an ear infection, trauma or upper respiratory tract infection or may have an insidious onset related to chronic middle ear disease, otosclerosis or a tumour of the naso-pharynx. Earwax is a very common cause of a conductive hearing loss which may present suddenly when the wax blocks sound from getting through the external ear canal to the middle and inner ear. Diagnosis
Diagnosis requires a detailed history, local examination of the ear, nose, throat and neck, and detailed hearing tests. In children a more detailed examination may be required if the hearing loss is congenital. Otoscopy
Examination of the external ear canal and ear drum is important and may help identify problems located in the outer ear up to the tympanic membrane. Differential testing
For basic screening, a conductive hearing loss can be identified using the Rinne test with a 256 Hz tuning fork. The Rinne test, in which a patient is asked to say whether a vibrating tuning fork is heard more loudly adjacent to the ear canal (air conduction) or touching the bone behind the ear (bone conduction), is negative indicating that bone conduction is more effective that air conduction. A normal, or positive, result, is when air conduction is more effective than bone conduction.