Impaired lysosomal acidity maintenance in acid lipase-deficient cells leads to defective autophagy.

The lysosome is an acid organelle that contains a variety of hydrolytic enzymes and plays a significant role in intracellular degradation to maintain cellular homeostasis. Genetic variants in lysosome-related genes can lead to severe congenital diseases, such as lysosomal storage diseases. In the present study, we investigated the impact of depleting lysosomal acid lipase A (LIPA), a lysosomal esterase that metabolizes esterified cholesterol or triglyceride, on lysosomal function. Under nutrient-rich conditions, LIPA gene KO (LIPAKO) cells exhibited impaired autophagy, whereas, under starved conditions, they showed normal autophagy. The cause underlying the differential autophagic activity was increased sensitivity of LIPAKO cells to ammonia, which was produced from l-glutamine in the medium. Further investigation revealed that ammonia did not affect upstream signals involved in autophagy induction, autophagosome-lysosome fusion, and hydrolytic enzyme activities in LIPAKO cells. On the other hand, LIPAKO cells showed defective lysosomal acidity upon ammonia loading. Microscopic analyses revealed that lysosomes of LIPAKO cells enlarged, whereas the amount of lysosomal proton pump V-ATPase did not proportionally increase. Since the enlargement of lysosomes in LIPAKO cells was not normalized under starved conditions, this is the primary change that occurred in the LIPAKO cells, and autophagy was affected by impaired lysosomal function under the specific conditions. These findings expand our comprehension of the pathogenesis of Wolman's disease, which is caused by a defect in the LIPA gene, and suggest that conditions, such as hyperlipidemia, may easily disrupt lysosomal functions.

Early diagnosis of infantile-onset lysosomal acid lipase deficiency in the advent of available enzyme replacement therapy.

BACKGROUND: Lysosomal acid lipase deficiency (LAL-D) is an autosomal recessive disorder that can present as a severe, infantile form also known as Wolman disease. We sought to determine the outcomes and clinical needs of infants diagnosed with LAL-D, treated with enzyme replacement therapy (ERT). METHODS: A chart review was conducted on two infantile-onset LAL-D patients to determine clinical outcomes based on laboratory results, abdominal imaging, growth and dietary records, cardiology, endocrinology, ophthalmology, hematology, and neurocognitive evaluations. RESULTS: Two patients, both diagnosed and treated before 6 months old, demonstrated clinical improvement following weekly ERT. They required dosage increases to optimize growth and symptomatology. Both received a formula low in long chain triglycerides and high in medium chain triglycerides, an intervention that allowed significant catch-up growth. Patient 1 required treatment for partial adrenal insufficiency and hypothyroidism. Both patients demonstrated reduction in liver and spleen size and varying degrees of improved liver function. Neither experienced serious adverse reactions to ERT. CONCLUSION: ERT has led to longer and healthier survival of affected infants. It is imperative that dietary interventions and systemic clinical care become integral to the management. Continued evidence of survival and clinical improvement in this population, coupled with available mass spectrometry enzyme assay from dried blood spots, raises the question of this rare and possibly underdiagnosed disorder's candidacy for newborn screening.

Specific Substrate for the Assay of Lysosomal Acid Lipase.

BACKGROUND: Deficiency of lysosomal acid lipase (LAL) causes Wolman disease and cholesterol ester storage disease. With the recent introduction of enzyme replacement therapy to manage LAL deficiency comes the need for a reliable assay of LAL enzymatic activity that can be applied to dried blood spots (DBS). METHODS: We prepared and tested a library of analogs of palmitoyl 4-methylumbelifferyl esters to find a highly active and specific substrate for LAL in DBS. The LAL assay was optimized leading to both LC-MS/MS and fluorometric assay of LAL. We tested the new assay on DBS from healthy and LAL-deficient patients. RESULTS: The ester formed between palmitic acid and 4-propyl-8-methyl-7-hydroxycoumarin (P-PMHC) was found to be >98% selective for LAL in DBS based on the sensitivity of its activity to the LAL-specific inactivator Lalistat-2 and the fact that the activity was close to zero using DBS from patients previously shown to be LAL-deficient. Use of P-PMHC and heavy isotope-labeled internal standard with optimized assay conditions led to an approximately 2-fold increase in the specific activity of LAL compared with the previously reported LAL assay. Patients deficient in LAL were readily distinguished from normal persons with the new LAL assay using UPLC-MS/MS or fluorometric assay platforms. CONCLUSIONS: The new assay can measure LAL in DBS with a single measurement compared with the previous method involving 2 assays done in parallel.

Molecular and clinical characterization of a series of patients with childhood-onset lysosomal acid lipase deficiency. Retrospective investigations, follow-up and detection of two novel LIPA pathogenic variants.

BACKGROUND AND AIMS: Childhood/Adult-onset Lysosomal Acid Lipase Deficiency (LAL-D) is a recessive disorder due to loss of function variants of LAL, the enzyme which hydrolyses cholesteryl esters, derived from internalized apoB containing lipoproteins. The disease is characterized by multi-organ involvement including the liver, spleen, intestine and cardiovascular system. The aim of this study was the clinical and molecular characterization of 14 (13 unrelated) previously unreported patients with childhood-onset LAL-D. METHODS: Data collected included clinical and laboratory investigations, liver imaging, liver biopsy and LIPA gene analysis. The response to lipid-lowering medications, liver transplantation and enzyme replacement therapy (ERT) was reported for some patients. RESULTS: LAL-D was suspected at 4.4 ± 3.3 years of age for the presence of hepatomegaly, elevated serum transaminases and hypercholesterolemia, and was confirmed by liver biopsy/imaging and LAL assay. The follow up period ranged from 3 to 40 years (mean 7.8 ± 4.0 years in 13 cases). Patients treated with statins with or without ezetimibe showed 28% reduction of plasma LDL-cholesterol without a tangible effect on liver enzymes; some patients receiving ERT showed normalized lipoprotein profile and transaminase levels. The common c.894G > A variant was observed in homozygosity or compound heterozygosity in 10 patients. We found seven previously reported variants: p.(Trp140*), p.(Arg218*), p.(Gly266*), p.(Thr288Ile), p.(Leu294Ser), p.(His295Tyr) and p.(Gly342Arg) and two novel variants: p.(Asp345Asn), affecting the LAL catalytic triad, and c.229+3A > C, affecting splicing. Homozygosity for p.(Thr288Ile) or c.229+3A > C was associated with a severe phenotype. CONCLUSIONS: This study provides additional data on the features of childhood-onset LAL-D and describes two novel pathogenic variants of the LIPA gene.

Identification and metabolic profiling of patients with lysosomal acid lipase deficiency.

BACKGROUND: Lysosomal acid lipase (LAL), encoded by the LIPA gene, catalyzes the intracellular hydrolysis of cholesteryl esters and triglycerides in hepatocytes and macrophages. LIPA defects cause accumulation of these lipids in lysosomes. LAL deficiency (LAL D) presents and progresses as a continuum with dyslipidemia, hepatomegaly, and liver fibrosis. OBJECTIVE: To improve the understanding of the genetic basis of LAL D, an underappreciated cause of dyslipidemia and cirrhosis, we studied DNA samples from patients with various phenotypes of dyslipidemia. METHODS: Participants (N = 1357) were identified by lipid profiles and screened for the common disease causing LIPA exon 8 skipping splice-site mutation (c.894G>A; p.Ser275_Gln298del; rs116928232). RESULTS: Six patients were heterozygous for this variant. Complete LIPA sequencing revealed a patient, subsequently confirmed to have LAL D, with a heterozygous frameshift mutation involving deletion of exon 4 (p.Gly77Valfs*17 c.230-106_c.428+541del). A family study revealed a sister with the same genotype and phenotype. Genetic, clinical, and lipoprotein profiles of these sisters plus 6 additional family members are reported. Profiles of 2 other LAL D patients monitored for 2 decades are presented. Cholesterol homeostasis was studied to investigate rates of cholesterol synthesis and absorption in 4 LAL D patients. High-density lipoprotein (HDL) subspecies were also analyzed. CONCLUSIONS: We used this LIPA sequencing strategy (detection of the relatively common exon 8 variant followed by complete gene sequencing to identify additional mutations) as a means to further elucidate the genetic basis of LAL D among individuals with a suggestive clinical phenotype.

Novel LIPA mutations in Mexican siblings with lysosomal acid lipase deficiency.

Lysosomal acid lipase (LAL) deficiency is an under-recognized lysosomal disease caused by deficient enzymatic activity of LAL. In this report we describe two affected female Mexican siblings with early hepatic complications. At two months of age, the first sibling presented with alternating episodes of diarrhea and constipation, and later with hepatomegaly, elevated transaminases, high levels of total and low-density lipoprotein cholesterol, and low levels of high-density lipoprotein. Portal hypertension and grade 2 esophageal varices were detected at four years of age. The second sibling presented with hepatomegaly, elevated transaminases and mildly elevated low-density lipoprotein and low high-density lipoprotein at six months of age. LAL activity was deficient in both patients. Sequencing of LIPA revealed two previously unreported heterozygous mutations in exon 4: c.253C>A and c.294C>G. These cases highlight the clinical continuum between the so-called Wolman disease and cholesteryl ester storage disease, and underscore that LAL deficiency represents a single disease with a degree of clinical heterogeneity.

Expression and functional characterization of human lysosomal acid lipase gene (LIPA) mutation responsible for cholesteryl ester storage disease (CESD) phenotype.

Lysosomal acid lipase (LAL) is a serine hydrolase which hydrolyzes cholesteryl ester and triglycerides delivered to the lysosomes into free cholesterol and free fatty acids. Mutations in the LAL gene (LIPA) result in accumulation of triglycerides and cholesterol esters in various tissues of the body, leading to pathological conditions such as Wolman's disease (WD) and cholesteryl ester storage disease (CESD). CESD patients homozygous for His295Tyr (H295Y) mutation have less than 5% of normal LAL activity. To shed light on the molecular basis for this loss-of-function phenotype, we have generated the recombinant H295Y enzyme and studied its biophysical and biochemical properties. No significant differences were observed in the expression levels or glycosylation patterns between the mutant and the wild type LAL. However, the H295Y mutant displayed only residual enzymatic activity (<5%) compared to the wild type. While wild type LAL is mostly a monomer at pH 5.0, the vast majority H295Y exists as a high molecular soluble aggregate. Besides, the H295Y mutant has a 20°C lower melting temperature compared to the wild type. Transient expression studies in WD fibroblasts showed that mutation of His295 to other amino acids resulted in a significant loss of enzymatic activity. A homology model of LAL revealed that His295 is located on an α-helix of the cap domain and could be important for tethering it to its core domain. The observed loss-of-function phenotype in CESD patients might arise from a combination of protein destabilization and the shift to a non-functional soluble aggregate.

[Wolman disease with novel mutation of LIPA gene in a Chinese infant].

OBJECTIVE: To explore the clinical characteristics of Wolman disease and diagnostic methods using enzymatic and molecular analysis. METHOD: Lysosomal acid lipase activity was measured using 4-methylumbelliferyl oleate in the leukocytes of an infant suspected of Wolman disease and LIPA gene mutational analysis was performed by PCR and direct sequencing in the proband and his parents. After the diagnosis was confirmed, the clinical, biochemical, radiological and histopathological findings in this case of Wolman disease were retrospectively reviewed. RESULT: The sixteen-day-old boy was failing to thrive with progressive vomiting, abdominal distention and hepatosplenomegaly. Abdominal X-ray revealed adrenal calcifications which were confirmed on abdominal CT scan. Xanthomatosis were observed on enlarged liver, spleen and lymph nodes during abdominal surgery. Liver and lymph node biopsy showed foamy histiocytes. The lysosomal acid lipase activity in leukocytes was 3.5 nmol/(mg·h) [control 35.5 - 105.8 nmol/(mg·h)]. Serum chitotriosidase activity was 315.8 nmol/(ml·h) [control 0 - 53 nmol/(ml·h)]. The patient was homozygote for a novel insert mutation allele c.318 ins T, p. Phe106fsX4 in exon 4 on LIPA gene. His both parents were carriers of the mutation. CONCLUSION: The clinical features of Wolman disease include early onset of vomiting, abdominal distention, growth failure, hepatosplenomegaly and bilateral adrenal calcification after birth. A plain abdominal X-ray film should be taken to check for the typical pattern of adrenal calcification in suspected cases of Wolman disease. The enzymatic and molecular analyses of lysosomal acid lipase can confirm the diagnosis of Wolman disease.

Lysosomal lipase deficiency: molecular characterization of eleven patients with Wolman or cholesteryl ester storage disease.

Wolman Disease (WD) and cholesteryl ester storage disease (CESD) represent two distinct phenotypes of the same recessive disorder caused by the complete or partial deficiency of lysosomal acidic lipase (LAL), respectively. LAL, encoded by the LIPA gene, hydrolyzes cholesteryl esters derived from cell internalization of plasma lipoproteins. WD is a rapidly progressive and lethal disease characterized by intestinal malabsorption, hepatic and adrenal failure. CESD is characterized by hepatic fibrosis, hyperlipidemia and accelerated atherosclerosis. Aim of the study was the identification of LIPA mutations in three WD and eight CESD patients. The WD patients, all deceased before the first year of age, were homozygous for two novel mutations (c.299+1G>A and c.419G>A) or a mutation (c.796G>T) previously reported as compound heterozygosity in a CESD patient. The two mutations (c.419G>A and c.796G>T) resulting in truncated proteins (p.W140* and p.G266*) and the splicing mutation (c.229+1G>A) were associated with undetectable levels of LIPA mRNA in fibroblasts. All eight CESD patients carried the common mutation c.894G>A known to result not only in a major non-functional transcript with the skipping of exon 8 (p.S275_Q298del), but also in a minor normally spliced transcript producing 5-10% residual LAL activity. The c.894G>A mutation was found in homozygosity in four patients and, as compound heterozygosity, in association with a known (p.H295Y and p.G342R) or a novel (p.W140*) mutation in four other CESD patients. Segregation analysis performed in all patients harboring c.895G>A showed its occurrence on the same haplotype suggesting a common founder ancestor. The other WD and CESD mutations were associated with different haplotypes.

Wolman disease: diagnosis by leucocyte acid lipase estimation.

Wolman disease is a rare fatal autosomal recessive disorder caused by absence of acid lipase enzyme leading to accumulation of cholesterol ester. Hepatosplenomegaly is a constant feature and occurs as early as fourth day of life. Progressive mental deterioration may occur after few weeks of onset of symptoms. Adrenal calcification seen on X-ray abdomen, USG or CT scan is the hallmark of Wolman disease. For the first time in Indian literature, the authors report a case of Wolman disease that was confirmed by acid lipase enzyme estimation.

Wolman disease and cholesteryl ester storage disease diagnosed by histological and ultrastructural examination of intestinal and liver biopsy.

Deficient activity of lysosomal acid lipase (LAL) results in massive accumulation of cholesteryl esters and triglycerides in most tissues of the body. The deficiency state is expressed in two major phenotypes: Wolman disease (WD) and cholesteryl ester storage disease (CESD). WD occurs in infancy and is nearly always fatal before the age of 1 year, whereas CESD can be more benign and may not be detected until adulthood. Since there are no specific routine laboratory observations that suggest these metabolic diseases, diagnosis is based on the clinical picture combined with LAL deficiency in cultured skin fibroblasts or peripheral lymphocytes. Both disorders are rather rare, considering that about a hundred of cases have been described up to now. This study describes the histological and ultrastructural aspects disclosed by intestinal or liver biopsy in three cases of WD and in two cases of CESD. Furthermore, it emphasizes the role of morphological findings in pointing the diagnosis towards a metabolic storage disease.

Lysosomal acid lipase deficiency: correction of lipid storage by adenovirus-mediated gene transfer in mice.

Lysosomal acid lipase (LAL) is the essential enzyme for hydrolysis of triglycerides (TGs) and cholesteryl esters (CEs) in lysosomes. Its deficiency produces two human phenotypes: Wolman disease (WD) and cholesteryl ester storage disease (CESD). The LAL null (lal(-/-)) mouse mimicks aspects of human WD and CESD. The potential for gene therapy of LAL deficiency was tested with first-generation adenoviral vectors containing human LAL cDNA (Ad-hLAL) by intravenous injection into lal(-/-) mice. Compared with phosphate-buffered saline-injected controls, the mice receiving Ad-hLAL had increased hepatic LAL activity, decreased hepatomegaly, and normalization of histopathology. hLAL protein and mRNA were detected by immunohistochemical staining and in situ hybridization in hepatic parenchymal and sinusoid lining cells, splenic sinusoidal cells, lung macrophages, and adrenal cortical cells. Mice showed TG reductions in liver, spleen, and small intestine of 68, 54, and 50%, respectively, and cholesterol reductions of 55, 52, and 34%, respectively, at 20 days postinjection. These studies provide the basis for the use of gene therapy, in the form of gene transfer via intravenously administered adenovirus, to correct deficiency states, such as WD and CESD, and histopathology of a variety of tissues.

Enzyme therapy for lysosomal acid lipase deficiency in the mouse.

Lysosomal acid lipase (LAL) is the critical enzyme for the hydrolysis of the triglycerides (TG) and cholesteryl esters (CE) delivered to lysosomes. Its deficiency produces two human phenotypes, Wolman disease (WD) and cholesteryl ester storage disease (CESD). A targeted disruption of the LAL locus produced a null (lal( -/-)) mouse model that mimics human WD/CESD. The potential for enzyme therapy was tested using mannose terminated human LAL expressed in Pichia pastoris (phLAL), purified, and administered by tail vein injections to lal( -/-) mice. Mannose receptor (MR)-dependent uptake and lysosomal targeting of phLAL were evidenced ex vivo using competitive assays with MR-positive J774E cells, a murine monocyte/macrophage line, immunofluorescence and western blots. Following (bolus) IV injection, phLAL was detected in Kupffer cells, lung macrophages and intestinal macrophages in lal( -/-) mice. Two-month-old lal( -/-) mice received phLAL (1.5 U/dose) or saline injections once every 3 days for 30 days (10 doses). The treated lal( -/-) mice showed nearly complete resolution of hepatic yellow coloration; hepatic weight decreased by approximately 36% compared to PBS-treated lal( -/-) mice. Histologic analyses of numerous tissues from phLAL-treated mice showed reductions in macrophage lipid storage. TG and cholesterol levels decreased by approximately 50% in liver, 69% in spleen and 50% in small intestine. These studies provide feasibility for LAL enzyme therapy in human WD and CESD.

Phenotypic correction of lipid storage and growth arrest in wolman disease fibroblasts by gene transfer of lysosomal acid lipase.

Wolman disease is a lethal lysosomal storage disease due to deficiency of lysosomal acid lipase (LAL). Wolman disease is characterized by pronounced hepatic involvement while neurological symptoms are uncommon, making Wolman disease an attractive candidate for liver-directed gene therapy. This study was performed to test the effects of gene replacement in fibroblasts lacking LAL, using a recombinant adenovirus encoding the human LAL cDNA (AdhLAL). Human fibroblasts from a Wolman disease patient were infected with AdhLAL and showed a dose-dependent increase in LAL protein and activity up to 5-fold above levels in control fibroblasts. Furthermore, 72 hr after infection with AdhLAL there was a dose-dependent correction of the severe lipid storage phenotype of Wolman disease fibroblasts. Electron microscopy confirmed significant correction of the lysosomal lipid storage in AdhLAL-infected Wolman disease fibroblasts at the ultrastructural level. Intravenous injection of AdhLAL into wild-type mice resulted in a 13.5-fold increase in hepatic LAL activity, and overexpression of LAL was not associated with toxic side effects. These data demonstrate high-level lysosomal expression of recombinant LAL in vitro and in vivo and show the feasibility of gene therapeutic strategies for the treatment of Wolman disease.

Lysosomal acid lipase mutations that determine phenotype in Wolman and cholesterol ester storage disease.

Mechanisms producing the divergent phenotypes, Wolman disease (WD) and cholesterol ester storage disease (CESD), associated with the genetic deficiency of human lysosomal acid lipase/cholesterol ester hydrolase (hLAL) function were investigated with the determination of HLAL activity levels, mRNA and protein expression, and defects in structural gene sequences in cells from three WD and five CESD patients. Measured with natural substrates, HLAL activities were all below 2% of normal, regardless of phenotype. Immunoblotting showed a lack of detectable hLAL protein in all mutant fibroblasts. Four CESD, but no WD genomes contained at least one allele with a specific exon 8 splice junction mutation, c.894 G>A, that encodes a shortened form of hLAL mRNA. Other CESD mutations were identical in type to the WD defects: nucleotide deletions (positions 397, 684, 980), insertions (594), or substitutions (193, 347) that result in premature terminations precluding any function. The only exception was a substitution at nucleotide 866 in the CESD case without an exon 8 splicing mutation; expression of the predicted S289C change in a transfection assay produced a low, but clearly measurable, level of acid esterase activity. Although it is not easily demonstrated in conventional assays, CESD is distinct from WD in that at least one mutant allele has the potential to produce enough residual enzymatic function to ameliorate the phenotype; in the majority of CESD cases this may come from a single, easily detected, splicing mutation in one allele.

Molecular defects underlying Wolman disease appear to be more heterogeneous than those resulting in cholesteryl ester storage disease.

Human lysosomal acid lipase/cholesteryl ester hydrolase (hLAL) is essential for the intralysosomal metabolism of cholesteryl esters and triglycerides taken up by receptor-mediated endocytosis of lipoprotein particles. The key role of the enzyme in intracellular lipid homeostasis is illustrated by two lysosomal storage diseases inherited as autosomal recessive traits. Wolman disease, associated with deficient hLAL activity, leads to massive intracellular substrate accumulation and is always fatal in early infancy. Cholesteryl ester storage disease (CESD), in contrast, is characterized by very low levels of enzymic activity sufficient to allow survival of the affected patients into adulthood. In order to elucidate the underlying molecular defects in Wolman disease, we have characterized the hLAL gene in two female Wolman patients of German and Turkish origin by SSCP and DNA sequence analysis. Our results demonstrate that the German proband was compound heterozygous for an 8-bp deletion in exon 3 and a 2-bp deletion in exon 4 of the hLAL gene. These frameshift mutations lead to protein truncation at amino acid positions 24 and 116 and to complete loss of hydrolytic activity. The Turkish proband, in contrast, was homozygous for a G(1064)-->T substitution in exon 10 of the hLAL gene which converts the completely conserved glycine (GGG) residue at position 321 of the mature enzyme to tryptophan (TGG). In vitro expression of the hLAL(Gly(321)-->Trp) cDNA construct revealed that the amino acid replacement results in a more than 99% reduction of neutral lipid hydrolysis. The mutations provide new insights into the molecular basis of Wolman disease which is apparently more heterogeneous at the genetic level than cholesteryl ester storage disease.-Lohse, P., S. Maas, P. Lohse, A. C. Sewell, O. P. van Diggelen, and D. Seidel. Molecular defects underlying Wolman disease appear to be more heterogeneous than those resulting in cholesteryl ester storage disease.

Targeted disruption of the mouse lysosomal acid lipase gene: long-term survival with massive cholesteryl ester and triglyceride storage.

Lysosomal acid lipase (LAL) is essential for the hydrolysis of the triglycerides and cholesteryl esters in lysosomes. Its deficiency produces two phenotypes, a severe infantile-onset variant, Wolman disease (WD), and a later onset variant, cholesteryl ester storage disease (CESD). A mouse model with a LAL null mutation was produced by targeting disruption of the mouse gene. Homozygote knockout mice (lal -/lal-) produce no LAL mRNA, protein or enzyme activity. The lal-/lal- mice are born in Mendelian ratios, are normal appearing at birth, and follow normal development into adulthood. However, massive accumulation of triglycerides and cholesteryl esters occurs in several organs. By 21 days, the liver develops a yellow-orange color and is approximately 1.5-2.0x larger than normal. The accumulated cholesteryl esters and triglycerides are approximately 30-fold greater than normal. The lal+/lal- mice have approximately 50% of normal LAL activity and do not show lipid accumulation. Male and female lal-/lal- mice are fertile and can be bred to produce progeny. This mouse model is a phenotypic model of human CESD, and a biochemical and histopathologic mimic of human WD. The lal-/lal- mice provide a model to determine the role of LAL in lipid metabolism and the pathogenesis of its deficiency states.

New lysosomal acid lipase gene mutants explain the phenotype of Wolman disease and cholesteryl ester storage disease.

Deficiency of lysosomal acid lipase (LAL) leads to either Wolman disease (WD) or the more benign cholesteryl ester storage disease (CESD). To identify the molecular basis of the different phenotypes we have characterised the LAL gene mutations in three new patients with LAL deficiency. A patient with WD was homozygote for a null allele Y303X. The other two patients, with CESD, presented either homozygosity for T267I or compound heterozygosity consisting of Q64R and an exon 8 donor splice site substitution (G-->A in position -1). The mutants T267I and Q64R and the previously reported L273S, G66V, and H274Y CESD substitutions, overexpressed in stable clones, were found to be fully glycosylated and show an enzymatic activity of 3-8% of that of normal LAL. On the other hand, the delta254-277 mutant protein derived from exon 8 skipping and the Y303X protein were totally inactive. By transient transfection of hybrid minigene constructs, the CESD G-->A (-1) substitution resulted in partial exon inclusion, thus allowing the production of a small amount of normal LAL mRNA and hence of a functional enzyme. In contrast, a G-->A substitution observed in WD at position + 1 of the same exon 8 donor site resulted in complete exon skipping and the sole production of an inactive delta254-277 protein. In conclusion, LAL genotypes determine the level of residual enzymatic activity, thus explaining the severity of the phenotype.

Altered mononuclear phagocyte differentiation associated with genetic defects of the lysosomal acid lipase.

Multiparameter flow cytometry reveals a complex heterogeneity of mononuclear phagocyte differentiation within the peripheral blood compartment. In this study, the relation of abnormal cellular lipid metabolism to the phenotype of peripheral blood mononuclear phagocytes, which finally may be related to atherogenesis, was analyzed using recently characterized autosomal recessive defects of lysosomal acid lipase (LAL) expression as model system. The reduction of LAL activity in nine heterozygote, disease free carriers of mutations from two cholesteryl ester storage disease (CESD) pedigrees and the family of a patient with Wolman disease was associated with an increased fraction of monocytes which expressed CD56 (N-CAM) (4.1 +/- 2.7% of monocytes, compared to 2.2 +/- 0.5% in ten controls, P < 0.05), an antigen characteristic of immature myeloid cells, suggesting an increased turnover of monocytes. Furthermore, a trend was observed towards an enhanced blood pool of more mature mononuclear phagocytes which show decreased expression of the 55 kD lipopolysaccharide receptor (CD14) together with either expression of the Fc-gamma-receptor III (CD16) or a high expression of CD33. A similar phenotype of peripheral mononuclear phagocytes was observed in the two CESD patients analyzed. In conclusion, our data suggest that these monogenetic defects of lysosomal lipoprotein metabolism are associated with complex alterations of mononuclear phagocyte differentiation and extravasation.