Bassen Kornzweig syndrome [keywords]
- Structure-function analyses of microsomal triglyceride transfer protein missense mutations in abetalipoproteinemia and hypobetalipoproteinemia subjects. [JOURNAL ARTICLE]
- Biochim Biophys Acta 2016 Jul 31; 1861(11):1623-1633.
We describe two new hypolipidemic patients with very low plasma triglyceride and apolipoprotein B (apoB) levels with plasma lipid profiles similar to abetalipoproteinemia (ABL) patients. In these patients, we identified two previously uncharacterized missense mutations in the microsomal triglyceride transfer protein (MTP) gene, R46G and D361Y, and studied their functional effects. We also characterized three missense mutations (H297Q, D384A, and G661A) reported earlier in a familial hypobetalipoproteinemia patient. R46G had no effect on MTP expression or function and supported apoB secretion. H297Q, D384A, and G661A mutants also supported apoB secretion similarly to WT MTP. Contrary to these four missense mutations, D361Y was unable to support apoB secretion. Functional analysis revealed that this mutant was unable to bind protein disulfide isomerase (PDI) or transfer lipids. The negative charge at residue 361 was critical for MTP function as D361E was able to support apoB secretion and transfer lipids. D361Y most likely disrupts the tightly packed middle α-helical region of MTP, mitigates PDI binding, abolishes lipid transfer activity, and causes ABL. On the other hand, the hypolipidemia in the other two patients was not due to MTP dysfunction. Thus, in this study of five missense mutations spread throughout MTP's three structural domains found in three hypolipidemic patients, we found that four of the mutations did not affect MTP function. Thus, novel mutations that cause severe hypolipidemia probably exist in other genes in these patients, and their recognition may identify novel proteins involved in the synthesis and/or catabolism of plasma lipoproteins.
- Identification of novel APOB mutations by targeted next-generation sequencing for the molecular diagnosis of familial hypobetalipoproteinemia. [Journal Article]
- Atherosclerosis 2016 Jul.:52-6.
Familial hypobetalipoproteinemia (FHBL) is a co-dominant disorder characterized by decreased plasma levels of LDL-cholesterol and apolipoprotein B (ApoB). Currently, genetic diagnosis in FHBL relies largely on Sanger sequencing to identify APOB and PCSK9 gene mutations and on western blotting to detect truncated ApoB species.Here, we applied targeted enrichment and next-generation sequencing (NGS) on a panel of three FHBL genes and two abetalipoproteinemia genes (APOB, PCSK9, ANGPTL3, MTTP and SAR1B).In this study, we identified five likely pathogenic heterozygous rare variants. These include four novel nonsense mutations in APOB (p.Gln845*, p.Gln2571*, p.Cys2933* and p.Ser3718*) and a rare variant in PCSK9 (Minor Allele Frequency <0.1%). The affected family members tested were shown to be carriers, suggesting co-segregation with low LDL-C.Our study further demonstrates that NGS is a reliable and practical approach for the molecular screening of FHBL-causative genes that may provide a mean for deciphering the genetic basis in FHBL.
- Microsomal triglyceride transfer protein gene mutations in Turkish children: A novel mutation and clinical follow up. [Journal Article]
- Indian J Gastroenterol 2016 May; 35(3):236-41.
Abetalipoproteinemia (ABL; OMIM 200100) is a rare autosomal recessive disease that affects the absorption of dietary fats and fat soluble vitamins. Here, we describe the clinical and genetic characteristics of three patients with ABL. Two patients (patients 1 and 2) who were carriers of the c.398-399delAA mutation (previously known mutation) had developmental delay and hepatic steatosis developed at the age of five in patient 1. Patient 3 was the carrier of a novel mutation (g.10886-10902delAAGgtaagtttgtgttg in intron 3 and c.506A>T exon 5) in microsomal triglyceride transfer protein (MTP) gene and had hepatic steatosis.
- Chylomicrons: Advances in biology, pathology, laboratory testing, and therapeutics. [Journal Article, Research Support, Non-U.S. Gov't, Review]
- Clin Chim Acta 2016 Apr 1.:134-48.
The adequate absorption of lipids is essential for all mammalian species due to their inability to synthesize some essential fatty acids and fat-soluble vitamins. Chylomicrons (CMs) are large, triglyceride-rich lipoproteins that are produced in intestinal enterocytes in response to fat ingestion, which function to transport the ingested lipids to different tissues. In addition to the contribution of CMs to postprandial lipemia, their remnants, the degradation products following lipolysis by lipoprotein lipase, are linked to cardiovascular disease. In this review, we will focus on the structure-function and metabolism of CMs. Second, we will analyze the impact of gene defects reported to affect CM metabolism and, also, the role of CMs in other pathologies, such as atherothrombotic cardiovascular disease and diabetes mellitus. Third, we will provide an overview of the laboratory tests currently used to study CM disorders, and, finally, we will highlight current treatments in diseases affecting CMs.
- Homozygous familial hypobetalipoproteinemia: A Turkish case carrying a missense mutation in apolipoprotein B. [Journal Article, Research Support, Non-U.S. Gov't]
- Clin Chim Acta 2016 Jan 15.:185-90.
The autosomal co-dominant disorder familial hypobetalipoproteinemia (FHBL) may be due to mutations in the APOB gene encoding apolipoprotein B (apoB), the main constituent peptide of chylomicrons, very low and low density lipoproteins. We describe an 11month-old child with failure to thrive, intestinal lipid malabsorption, hepatic steatosis and severe hypobetalipoproteinemia, suggesting the diagnosis of homozygous FHBL, abetalipoproteinemia (ABL) or chylomicron retention disease (CMRD). The analysis of candidate genes showed that patient was homozygous for a variant (c.1594 C>T) in the APOB gene causing arginine to tryptophan conversion at position 505 of mature apoB (Arg505Trp). No mutations were found in a panel of other potential candidate genes for hypobetalipoproteinemia. In vitro studies showed a reduced secretion of mutant apoB-48 with respect to the wild-type apoB-48 in transfected McA-RH7777 cells. The Arg505Trp substitution is located in the βα1 domain of apoB involved in the lipidation of apoB mediated by microsomal triglyceride transfer protein (MTP), the first step in VLDL and chylomicron formation. The patient's condition improved in response to a low fat diet supplemented with fat-soluble vitamins. Homozygosity for a rare missense mutation in the βα1 domain of apoB may be the cause of both severe hypobetalipoproteinemia and intestinal lipid malabsorption.
- HYPERGLYCAEMIC HEMIBALLISMUS: IMPLICATIONS FROM CONNECTIVITY ANALYSIS FOR COGNITIVE IMPAIRMENTS. [Case Reports, Journal Article, Research Support, Non-U.S. Gov't]
- Ideggyogy Sz 2015 Nov 30; 68(11-12):417-21.
Hyperglycaemia induced movement disorders, such as hemiballism are rare disorders. The syndrome is characterised by the triad of hemiballism, contralateral T1-hyperintense striatal lesion and non-ketotic hyperglycaemia. Here we report a patient with untreated diabetes presenting with acute onset of hemiballism. MRI revealed T1 hyperintensity of the head of the caudate nucleus and the anterior putamen. The patient also had acantocytosis. Based on the detailed examination of the neuroradiological results and earlier findings we will discuss the pathomechanism. Based on previous findings microhemorrhages, extensive mineralisation, gemistocytic astrocytosis might play a role in the development of the imaging signs. The connectivity pattern of the striatal lesion showed extensive connections to the frontal cortex. In coexistence with that the most severe impairment was found on the phonemic verbal fluency task measuring frontal executive functions.
- Hypolipidemia in a Special Operations Candidate: Case Report and Review of the Literature. [Case Reports, Journal Article, Review]
- J Spec Oper Med 2015; 15(4):1-5.
A 19-year-old male military recruit who presented for a screening physical for US Naval Special Warfare Duty was found to have hypolipidemia. Medical history revealed mildly increased frequency of bowel movements, but was otherwise unremarkable. His presentation was most consistent with heterozygous familial hypobetalipoproteinemia (FHBL), and the patient was cleared for Special Operations duty.A literature search was conducted using PubMed/MEDLINE. Keywords included familial hypobetalipoproteinemia, heterozygous familial hypobetalipoproteinemia, abetalipoproteinemia, hypolipidemia, diving, special operations, and military. Results that included cases of familial hypobetalipoproteinemia were included.Review of the literature reveals that FHBL is a genetic disorder frequently, but not always, due to a mutation in the apolipoprotein B (apoB) gene. Those with the condition should be screened for ophthalmologic, neurologic, and gastrointestinal complications. Analysis of the disease, as well as the absence of reported cases of FHBL in diving and Special Operations, suggest there is minimal increased risk in diving and Special Operations for patients who are likely heterozygous, are asymptomatic, and have a negative workup for potential complications from the disease.Individuals with presumed or proven heterozygous FHBL seeking clearance for Special Operations duty should be given precautions, undergo careful questioning for history of disease-specific complications, and should have a baseline evaluation. If negative, it seems reasonable to clear the patient for Special Operations and diving.
- Update on the molecular biology of dyslipidemias. [Journal Article, Review]
- Clin Chim Acta 2016 Feb 15.:143-85.
Dyslipidemia is a commonly encountered clinical condition and is an important determinant of cardiovascular disease. Although secondary factors play a role in clinical expression, dyslipidemias have a strong genetic component. Familial hypercholesterolemia is usually due to loss-of-function mutations in LDLR, the gene coding for low density lipoprotein receptor and genes encoding for proteins that interact with the receptor: APOB, PCSK9 and LDLRAP1. Monogenic hypertriglyceridemia is the result of mutations in genes that regulate the metabolism of triglyceride rich lipoproteins (eg LPL, APOC2, APOA5, LMF1, GPIHBP1). Conversely familial hypobetalipoproteinemia is caused by inactivation of the PCSK9 gene which increases the number of LDL receptors and decreases plasma cholesterol. Mutations in the genes APOB, and ANGPTL3 and ANGPTL4 (that encode angiopoietin-like proteins which inhibit lipoprotein lipase activity) can further cause low levels of apoB containing lipoproteins. Abetalipoproteinemia and chylomicron retention disease are due to mutations in the microsomal transfer protein and Sar1b-GTPase genes, which affect the secretion of apoB containing lipoproteins. Dysbetalipoproteinemia stems from dysfunctional apoE and is characterized by the accumulation of remnants of chylomicrons and very low density lipoproteins. ApoE deficiency can cause a similar phenotype or rarely mutations in apoE can be associated with lipoprotein glomerulopathy. Low HDL can result from mutations in a number of genes regulating HDL production or catabolism; apoAI, lecithin: cholesterol acyltransferase and the ATP-binding cassette transporter ABCA1. Patients with cholesteryl ester transfer protein deficiency have markedly increased HDL cholesterol. Both common and rare genetic variants contribute to susceptibility to dyslipidemias. In contrast to rare familial syndromes, in most patients, dyslipidemias have a complex genetic etiology consisting of multiple genetic variants as established by genome wide association studies. Secondary factors, obesity, metabolic syndrome, diabetes, renal disease, estrogen and antipsychotics can increase the likelihood of clinical presentation of an individual with predisposed genetic susceptibility to hyperlipoproteinemia. The genetic profiles studied are far from complete and there is room for further characterization of genes influencing lipid levels. Genetic assessment can help identify patients at risk for developing dyslipidemias and for treatment decisions based on 'risk allele' profiles. This review will present the current information on the genetics and pathophysiology of disorders that cause dyslipidemias.