Biallelic mutations in the LIPA gene result in deficiency of lysosomal acid lipase (LAL), which underlies diverse phenotypes of cholesteryl ester storage disease (CESD). The most extreme and immediately life-threatening form of the disease occurs in infants as Wolman disease. Wolman disease was first characterized in 1961 by Dr M. Wolman, an Israeli physician who described 3 female siblings with generalized primary xanthomatosis, poor weight gain, gastrointestinal (GI) symptoms, hepatosplenomegaly, and adrenal calcifications who all died at the age of 3 months (1,2). The late-onset forms, first recognized in 1963 by Dr D.S. Fredrickson, exhibit extraordinarily broad phenotype diversity and many patients may be misdiagnosed for many years, often with nonalcoholic fatty liver disease (NAFLD) (3).
LAL is a key player in the low-density lipoprotein (LDL) receptor pathway, through its involvement in the hydrolysis of cholesterol esters in the lysosomes following receptor-mediated endocytosis of LDL. As the components of LDL are degraded by lysosomal hydrolases, action of LAL generates free cholesterol, which eventually mediates 3 regulatory functions to maintain cellular cholesterol homeostasis: downregulation of LDL receptors, inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, and stimulation of acyl cholesterol acyl transferase. Inherited deficiency of LAL leads to lysosomal accumulation of cholesterol esters (and triglycerides) and eventually failure of the LDL receptor pathway. Therefore, despite massive lysosomal accumulation of cholesterol esters, there is inappropriately high cellular (and whole body) synthesis of cholesterol. The gross phenotypic features include widespread accumulation of cholesterol ester-laden storage cells especially in the liver, the spleen, the lymph nodes, the thymus, and the small bowel. In addition, patients develop dyslipidemia and older patients experience accelerated coronary artery disease. Wolman disease phenotype occurs as a result of severe mutations in the LIPA gene and almost complete absence of LAL enzyme activity. These patients do not generally survive beyond the first 6 months, although there are a few case reports of longer-surviving patients following liver transplantation.
CESD phenotype demonstrates the widest phenotype variation, with patients being diagnosed in childhood or even in late adulthood. In the pediatric population, CESD may have a milder and nonspecific presentation. The symptoms of CESD can be highly variable. Hepatosplenomegaly, elevated transaminases, and type IIb hyperlipidemia with hypercholesterolemia, hypertriglyceridemia, and low high-density lipoprotein (HDL) are some common manifestations of CESD (4,5). In pediatric patients, vomiting, diarrhea, abdominal pain, and failure to thrive have been reported (6–8). In adult cases, CESD may manifest as early atherosclerosis and liver fibrosis (9,10). A common splicing mutation underlies CESD. Almost half of all reported patients with CESD in white populations have been found to harbor this splice junction mutation that leads to in-frame deletion of exon 8 (11–13). Data from the NHLBI Grand Opportunity Exome Sequencing Project suggest a prevalence of 1 of 150,000 to 1 of 300,000 of CESD in the white population (14). In addition, a population study in Germany estimated the carrier frequency of this mutation to be 1 in 200 and the prevalence of CESD to be as high as 25 per million (13).
The diagnosis of CESD is based on the measurement of LAL level in peripheral blood leukocytes (15,16). LAL activity is dramatically reduced in Wolman disease to <2% of normal controls. In late-onset CESD, residual enzyme activity is higher and the precise cutoff is still being established. In 2011, the normal LAL range in white blood cells was revised by Baylor Laboratories to 25 to 70 pmol · min−1 · mg−1 protein following a re-evaluation in response to increased awareness for CESD (17). LIPA gene sequencing is increasingly used in the evaluation of patients, especially when LAL enzyme activity results are equivocal (15,18). Ancillary tests that may suggest a diagnosis of CESD include increased chitotriosidase activity (19) and elevated transaminases.
Timely diagnosis of LAL deficiency is imperative for the devastating infantile form, Wolman disease, and late-onset CESD. For example, early diagnosis in Wolman disease would lead to lifesaving liver transplant and appropriate management of extrahepatic manifestations following transplantation. In late-onset CESD, timely diagnosis would lead to consideration of appropriate hypolipidemic therapy to reduce risk of atherosclerosis and monitoring for liver fibrosis. There is only 1 pathognomonic presentation of LAL deficiency, in the form of an infant with neonatal cholestasis associated with adrenal calcification (20). Unfortunately, all other presentations of LAL deficiency appear to lack specificity leading to misdiagnosis for many years. In addition, some patients may be asymptomatic and only found to have CESD incidentally (21). Because of these reasons, we believe that CESD may be underdiagnosed.
The aim of the study was to review the world literature on clinical phenotypes of LAL deficiency to determine common presenting symptoms and signs of CESD. The overarching aim was to define the gaps in our knowledge and help increase awareness of this disorder.
Cases of CESD were found using a PubMed search with the following key words: cholesterol ester storage disease, cholesteryl ester storage disease, fatty liver, and NAFLD. We reviewed all English-language publications from 1966 to June 2012 as well as citations from these articles for pediatric cases of CESD. All of the cases were reviewed and information regarding age, sex, presenting symptoms, and pertinent laboratory tests were recorded, if available.
Means and range were calculated for total cholesterol, LDL, HDL, and triglycerides. Frequency of cases with each symptom (hepatomegaly, splenomegaly, failure to thrive, gallbladder disease) was also calculated. If ≥1 laboratory value was mentioned for a specific case, the average of the values was used. Normal reference values were obtained from Harrison Principles of Internal Medicine. A symptom was considered present if the patient had it at any point during the course of the disease.
Seventy-one cases were culled from 39 published case reports from 1968 to June 2012 in English-language–published journals. There were 39 girls and 31 boys reported with CESD (55% vs 44%), 1 with unknown sex. Sixty-three percent of these patients (n = 40) presented with their first symptoms when they were younger than 5 years, 22% (n = 14) presented between ages 5 and 10 years, and 17% (n = 10) after 10 years of age.
Hepatomegaly was a constant feature in all of the patients, and the majority also had splenomegaly (86%). Serum transaminases were elevated in 80% of children with the pattern of nearly 2-fold elevation of AST compared with ALT. The average and range for each laboratory value and organ size are listed in Table 1.
Abnormalities in the lipid profile were also commonly seen. Elevated total cholesterol was noted in approximately 90% of children, elevated triglycerides in 48%, and low HDL in 85% of children. The average and range of lipid levels are also listed in Table 1. Atherosclerosis was noted in only 2 patients.
GI symptoms were noted in 30% of cases. Table 2 provides a breakdown of specific GI symptoms such as vomiting and diarrhea as well as a list of other symptoms and how frequently they were present.
Liver biopsies were completed in 51 of 71 cases with a majority of cases demonstrating cholesterol crystals, foamy cells with vacuolated cytoplasm, and lipid deposits. The degree of liver pathology varied from early stages with hepatocyte swelling to fibrosis and cirrhosis. Two-thirds of patients (63%) had variable degrees of liver fibrosis. Table 3 describes the frequency of each pathologic finding.
CESD has an estimated incidence as high as 1 in 40,000 (13) in the Germanic population and 1/300,000–1/500,000 in the white population. Using this latter and more conservative estimate would indicate that there are approximately 750 to 1500 patients with CESD in the United States and that CESD is presently underdiagnosed (14). Present treatment of CESD is limited with a primary aim to control cholesterol and prevent premature atherosclerosis with dietary changes and the use of lipid-lowering agents. Lipid-lowering agents such as statins, cholestyramine, and ezetimibe have been shown to be effective at decreasing lipid levels but are less effective at altering liver damage (22). Liver transplantation has also been used in a handful of children with severe liver disease (23,24). In animal models of CESD, enzyme replacement therapy has been extraordinarily effective in reversing the disease manifestations; presently, clinical trials are under way at several centers (www.clinicaltrials.gov identifiers: NCT01473875, NCT01488097, NCT01307098, NCT01371825). Sebelipasealfa, an enzyme replacement therapy for LAL deficiency, has been granted orphan status and Food and Drug Administration fast track designation and is presently being tested for efficacy in patients with CESD (25).
GI symptoms are common in patients with CESD because 30% of patients present with failure to thrive, vomiting, diarrhea, and other GI symptoms. NAFLD is also a common presentation because the majority of patients have elevated transaminases, and lipid droplets are seen in more than half of all cases.
CESD should be suspected in children with hepatomegaly and splenomegaly with elevated transaminases (AST > ALT), high total cholesterol, and an HDL level <30. Although type IIb hyperlipidemia is a common presentation for patients with CESD, <50% of patients in the case reports had elevated triglycerides with 90% and 85% of patients having high cholesterol and low HDL levels, respectively, which is consistent with this hyperlipidemia. Patients with NAFLD should also be screened for CESD, with particular attention paid to those children with a body mass index that is in the normal or overweight range. To confirm the diagnosis of CESD, LAL enzyme levels and LIPA gene analysis can be completed at clinical laboratories such as Baylor Medical Genetic Laboratories (17) and the Neurogenetics DNA/Biochemical Diagnostic Laboratory at Massachusetts General Hospital (www.dnalab.org).
Pediatric gastroenterologists and hepatologists as well as endocrinologists, cardiologists, and lipid specialists need to be educated and begin to use these findings when seeing patients to determine whether they need to be evaluated for possible CESD. Early treatment may curb the progression of atherosclerosis and new treatments may prevent the progression of liver disease.
Our study is limited to a retrospective review of the data presented in each of the case reports because the medical records for each of the children was not readily available. In addition, these cases may represent more severe presentations than may be typical for CESD. There are still many questions that need to be answered with regards to the diagnosis of CESD. With increased awareness and early diagnosis, more research can be done to identify more specific clinical and pathologic findings to make the diagnosis easier.
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