Lp X is an abnormal lipoprotein that is formed in cholestasis or LCAT deficiency
. Deficiencies or absences of lipoproteins are also readily demonstrated.
LCAT deficiency can be complete, resulting in a syndrome including corneal opacification, anemia, and renal disease, or partial, resulting in "fish-eye disease," in which corneal opacification is not accompanied by the anemia or renal component.
* Very low HDL cholesterol (<20 mg/dL or <0.52 mmol/L) in an ambulatory patient may be due to one of a few rare genetic conditions, including apoA-I deficiency, Tangier disease, and LCAT deficiency.
One of these patients was diagnosed with LCAT deficiency
of the lipid metabolism disorders, and another patient was diagnosed with KSS of the mitochondrial diseases.
It could also play a role in a rare hereditary disorder called familial LCAT deficiency
in which the LCAT enzyme is absent.
In both primary biliary cirrhosis and familial LCAT deficiency
, the low concentrations of hydrophobic core lipids are the cause for LpX formation.
Increased catabolism of LpAI and LpAI:AII leading to low HDL cholesterol concentrations is characteristic of Tangier disease and LCAT deficiency. Genetic deficiency of the ABCA1 transporter (Tangier disease) is associated with decreased cholesterol efflux and poor lipidation of pre-[beta] HDL, resulting in accelerated LpAI catabolism and increased CVD (124).
Role of LCAT in HDL remodeling: an investigation in LCAT deficiency states.
Consequently, as in Tangier disease, patients with LCAT deficiency
have increased pre-[[beta].sub.1] HDL and are thought to possibly also have an increased risk of cardiovascular disease, at least in the heterozygous state (30).
Importantly, patients with LCAT deficiency
and Tangier disease often have decreased LDL-C concentrations, which may be one factor offsetting the low HDL-C concentrations (7, 10).