The Genomic History of the Bronze Age Southern Levant.

We report genome-wide DNA data for 73 individuals from five archaeological sites across the Bronze and Iron Ages Southern Levant. These individuals, who share the "Canaanite" material culture, can be modeled as descending from two sources: (1) earlier local Neolithic populations and (2) populations related to the Chalcolithic Zagros or the Bronze Age Caucasus. The non-local contribution increased over time, as evinced by three outliers who can be modeled as descendants of recent migrants. We show evidence that different "Canaanite" groups genetically resemble each other more than other populations. We find that Levant-related modern populations typically have substantial ancestry coming from populations related to the Chalcolithic Zagros and the Bronze Age Southern Levant. These groups also harbor ancestry from sources we cannot fully model with the available data, highlighting the critical role of post-Bronze-Age migrations into the region over the past 3,000 years.

Bi-allelic variants in IPO8 cause a connective tissue disorder associated with cardiovascular defects, skeletal abnormalities, and immune dysregulation.

Dysregulated transforming growth factor TGF-ß signaling underlies the pathogenesis of genetic disorders affecting the connective tissue such as Loeys-Dietz syndrome. Here, we report 12 individuals with bi-allelic loss-of-function variants in IPO8 who presented with a syndromic association characterized by cardio-vascular anomalies, joint hyperlaxity, and various degree of dysmorphic features and developmental delay as well as immune dysregulation; the individuals were from nine unrelated families. Importin 8 belongs to the karyopherin family of nuclear transport receptors and was previously shown to mediate TGF-ß-dependent SMADs trafficking to the nucleus in vitro. The important in vivo role of IPO8 in pSMAD nuclear translocation was demonstrated by CRISPR/Cas9-mediated inactivation in zebrafish. Consistent with IPO8's role in BMP/TGF-ß signaling, ipo8-/- zebrafish presented mild to severe dorso-ventral patterning defects during early embryonic development. Moreover, ipo8-/- zebrafish displayed severe cardiovascular and skeletal defects that mirrored the human phenotype. Our work thus provides evidence that IPO8 plays a critical and non-redundant role in TGF-ß signaling during development and reinforces the existing link between TGF-ß signaling and connective tissue defects.

Evaluation of an automated genome interpretation model for rare disease routinely used in a clinical genetic laboratory.

PURPOSE: The analysis of exome and genome sequencing data for the diagnosis of rare diseases is challenging and time-consuming. In this study, we evaluated an artificial intelligence model, based on machine learning for automating variant prioritization for diagnosing rare genetic diseases in the Baylor Genetics clinical laboratory. METHODS: The automated analysis model was developed using a supervised learning approach based on thousands of manually curated variants. The model was evaluated on 2 cohorts. The model accuracy was determined using a retrospective cohort comprising 180 randomly selected exome cases (57 singletons, 123 trios); all of which were previously diagnosed and solved through manual interpretation. Diagnostic yield with the modified workflow was estimated using a prospective "production" cohort of 334 consecutive clinical cases. RESULTS: The model accurately pinpointed all manually reported variants as candidates. The reported variants were ranked in top 10 candidate variants in 98.4% (121/123) of trio cases, in 93.0% (53/57) of single proband cases, and 96.7% (174/180) of all cases. The accuracy of the model was reduced in some cases because of incomplete variant calling (eg, copy number variants) or incomplete phenotypic description. CONCLUSION: The automated model for case analysis assists clinical genetic laboratories in prioritizing candidate variants effectively. The use of such technology may facilitate the interpretation of genomic data for a large number of patients in the era of precision medicine.

Mutations in HOGA1 do Not Confer a Dominant Phenotype Manifesting as Kidney Stone Disease.

PURPOSE: The etiology of calcium-oxalate kidney stone formation remains elusive. Biallelic mutations in HOGA1 are responsible for primary hyperoxaluria type 3 and result in oxalate overproduction and kidney stone disease. Our previous study showed that carriers of HOGA1 mutations have elevated urinary levels of oxalate precursors. In this study we explored the possibility that mutations in HOGA1 confer a dominant phenotype in the form of kidney stone disease or hyperoxaluria. MATERIALS AND METHODS: An observational analytic case control study was designed to determine the prevalence of pathogenic HOGA1 mutations among adults with calcium-oxalate kidney stone disease. Given the high prevalence of HOGA1 mutations among Ashkenazi Jews, this group was evaluated separately. Carrier frequency of any of the 52 reported pathogenic mutations was compared to data derived from gnomAD for the corresponding ethnic group. Sanger sequencing of HOGA1 gene was performed on DNA samples from the following groups: 60 Ashkenazi Jews and 86 nonAshkenazi calcium-oxalate stone formers, 150 subjects with low and 150 with high urinary oxalate levels. RESULTS: The carrier prevalence of pathogenic mutations among the Ashkenazi Jews was 1.7% compared to 2.8% in the corresponding control group (p=0.9 OR=0.6 95% CI 0.01-3.51). We did not detect any mutation among the nonAshkenazi study group. No correlation was detected between hyperoxaluria and HOGA1 variants. CONCLUSIONS: This study shows that mutations in HOGA1 do not confer a dominant phenotype in the form of calcium-oxalate kidney stone disease or hyperoxaluria.

Whole-exome sequencing reveals POC5 as a novel gene associated with autosomal recessive retinitis pigmentosa.

Retinitis pigmentosa (RP), the most common form of inherited retinal degeneration, is associated with different groups of genes, including those encoding proteins involved in centriole and cilium biogenesis. Exome sequencing revealed a homozygous nonsense mutation [c.304_305delGA (p. D102*)] in POC5, encoding the Proteome Of Centriole 5 protein, in a patient with RP, short stature, microcephaly and recurrent glomerulonephritis. The POC5 gene is ubiquitously expressed, and immunohistochemistry revealed a distinct POC5 localization at the photoreceptor connecting cilium. Morpholino-oligonucleotide-induced knockdown of poc5 translation in zebrafish resulted in decreased length of photoreceptor outer segments and a decreased visual motor response, a measurement of retinal function. These phenotypes could be rescued by wild-type human POC5 mRNA. These findings demonstrate that Poc5 is important for normal retinal development and function. Altogether, this study presents POC5 as a novel gene involved autosomal recessively inherited RP, and strengthens the hypothesis that mutations in centriolar proteins are important cause of retinal dystrophies.

Germline variant in REXO2 is a novel candidate gene in familial pheochromocytoma.

Pheochromocytoma (PCC) is a rare, mostly benign tumour of the adrenal medulla. Hereditary PCC accounts for ~35% of cases and has been associated with germline mutations in several cancer susceptibility genes (e.g., KIF1B, SDHB, VHL, SDHD, RET). We performed whole-exome sequencing in a family with four PCC-affected patients in two consecutive generations and identified a potential novel candidate pathogenic variant in the REXO2 gene that affects splicing (c.531-1G>T (NM 015523.3)), which co-segregated with the phenotype in the family. REXO2 encodes for RNA exonuclease 2 protein and localizes to 11q23, a chromosomal region displaying allelic imbalance in PCC. REXO2 protein has been associated with DNA repair, replication and recombination processes and thus its inactivation may contribute to tumorigenesis. While the study suggests that this novel REXO2 gene variant underlies PCC in this family, additional functional studies are required in order to establish the putative role of the REXO2 gene in PCC predisposition.

Biallelic mutations in EXOC3L2 cause a novel syndrome that affects the brain, kidney and blood.

BACKGROUND: Dandy-Walker malformation features agenesis/hypoplasia of the cerebellar vermis, cystic dilatation of the fourth ventricle and enlargement of posterior fossa. Although Dandy-Walker malformation is relatively common and several genes were linked to the syndrome, the genetic cause in the majority of cases is unknown. OBJECTIVE: To identify the mutated gene responsible for Dandy-Walker malformation, kidney disease and bone marrow failure in four patients from two unrelated families. METHODS: Medical assessment, sonographic, MRI and pathological studies were used to define phenotype. Chromosomal microarray analysis and whole-exome sequence were performed to unravel the genotype. RESULTS: We report four subjects from two unrelated families with homozygous mutations in the Exocyst Complex Component 3-Like-2 gene (EXOC3L2).EXOC3L2 functions in trafficking of post-Golgi vesicles to the plasma membrane. In the first family a missense mutation in a highly conserved amino acid, p.Leu41Gln, was found in three fetuses; all had severe forms of Dandy-Walker malformation that was detectable by prenatal ultrasonography and confirmed by autopsy. In the second family, the affected child carried a nonsense mutation, p.Arg72*, and no detected protein. He had peritrigonal and cerebellar white matter abnormalities with enlargement of the ventricular trigones, developmental delay, pituitary hypoplasia, severe renal dysplasia and bone marrow failure. CONCLUSION: We propose that biallelic EXOC3L2 mutations lead to a novel syndrome that affects hindbrain development, kidney and possibly the bone marrow.

Primary Coenzyme Q deficiency Due to Novel ADCK3 Variants, Studies in Fibroblasts and Review of Literature.

Primary deficiency of coenzyme Q10 (CoQ10 ubiquinone), is classified as a mitochondrial respiratory chain disorder with phenotypic variability. The clinical manifestation may involve one or multiple tissue with variable severity and presentation may range from infancy to late onset. ADCK3 gene mutations are responsible for the most frequent form of hereditary CoQ10 deficiency (Q10 deficiency-4 OMIM #612016) which is mainly associated with autosomal recessive spinocerebellar ataxia (ARCA2, SCAR9). Here we provide the clinical, biochemical and genetic investigation for unrelated three nuclear families presenting an autosomal form of Spino-Cerebellar Ataxia due to novel mutations in the ADCK3 gene. Using next generation sequence technology we identified a homozygous Gln343Ter mutation in one family with severe, early onset of the disease and compound heterozygous mutations of Gln343Ter and Ser608Phe in two other families with variable manifestations. Biochemical investigation in fibroblasts showed decreased activity of the CoQ dependent mitochondrial respiratory chain enzyme succinate cytochrome c reductase (complex II + III). Exogenous CoQ slightly improved enzymatic activity, ATP production and decreased oxygen free radicals in some of the patient's cells. Our results are presented in comparison to previously reported mutations and expanding the clinical, molecular and biochemical spectrum of ADCK3 related CoQ10 deficiencies.

Big data analysis of human mitochondrial DNA substitution models: a regression approach.

BACKGROUND: We study Phylotree, a comprehensive representation of the phylogeny of global human mitochondrial DNA (mtDNA) variations, to better understand the mtDNA substitution mechanism and its most influential factors. We consider a substitution model, where a set of genetic features may predict the rate at which mtDNA substitutions occur. To find an appropriate model, an exhaustive analysis on the effect of multiple factors on the substitution rate is performed through Negative Binomial and Poisson regressions. We examine three different inclusion options for each categorical factor: omission, inclusion as an explanatory variable, and by-value partitioning. The examined factors include genes, codon position, a CpG indicator, directionality, nucleotide, amino acid, codon, and context (neighboring nucleotides), in addition to other site based factors. Partitioning a model by a factor's value results in several sub-models (one for each value), where the likelihoods of the sub-models can be combined to form a score for the entire model. Eventually, the leading models are considered as viable candidates for explaining mtDNA substitution rates. RESULTS: Initially, we introduce a novel clustering technique on genes, based on three similarity tests between pairs of genes, supporting previous results regarding gene functionalities in the mtDNA. These clusters are then used as a factor in our models. We present leading models for the protein coding genes, rRNA and tRNA genes and the control region, showing it is disadvantageous to separate the models of transitions/transversions, or synonymous/non-synonymous substitutions. We identify a context effect that cannot be attributed solely to protein level constraints or CpG pairs. For protein-coding genes, we show that the substitution model should be partitioned into sub-models according to the codon position and input codon; additionally we confirm that gene identity and cluster have no significant effect once the above factors are accounted for. CONCLUSIONS: We leverage the large, high-confidence Phylotree mtDNA phylogeny to develop a new statistical approach. We model the substitution rates using regressions, allowing consideration of many factors simultaneously. This admits the use of model selection tools helping to identify the set of factors best explaining the mutational dynamics when considered in tandem.

A null variant in the apolipoprotein L3 gene is associated with non-diabetic nephropathy.

Background: Inheritance of apolipoprotein L1 gene (APOL1) renal-risk variants in a recessive pattern strongly associates with non-diabetic end-stage kidney disease (ESKD). Further evidence supports risk modifiers in APOL1-associated nephropathy; some studies demonstrate that heterozygotes possess excess risk for ESKD or show earlier age at ESKD, relative to those with zero risk alleles. Nearby loci are also associated with ESKD in non-African Americans. Methods: We assessed the role of the APOL3 null allele rs11089781 on risk of non-diabetic ESKD. Four cohorts containing 2781 ESKD cases and 2474 controls were analyzed. Results: Stratifying by APOL1 risk genotype (recessive) and adjusting for African ancestry identified a significant additive association between rs11089781 and ESKD in each stratum and in a meta-analysis [meta-analysis P = 0.0070; odds ratio (OR) = 1.29]; ORs were consistent across APOL1 risk strata. The biological significance of this association is supported by the finding that the APOL3 gene is co-regulated with APOL1, and that APOL3 protein was able to bind to APOL1 protein. Conclusions: Taken together, the genetic and biological data support the concept that other APOL proteins besides APOL1 may also influence the risk of non-diabetic ESKD.

Deficiency of the sphingosine-1-phosphate lyase SGPL1 is associated with congenital nephrotic syndrome and congenital adrenal calcifications.

We identified two unrelated consanguineous families with three children affected by the rare association of congenital nephrotic syndrome (CNS) diagnosed in the first days of life, of hypogonadism, and of prenatally detected adrenal calcifications, associated with congenital adrenal insufficiency in one case. Using exome sequencing and targeted Sanger sequencing, two homozygous truncating mutations, c.1513C>T (p.Arg505*) and c.934delC (p.Leu312Phefs*30), were identified in SGPL1-encoding sphingosine-1-phosphate (S1P) lyase 1. SGPL1 catalyzes the irreversible degradation of endogenous and dietary S1P, the final step of sphingolipid catabolism, and of other phosphorylated long-chain bases. S1P is an intracellular and extracellular signaling molecule involved in angiogenesis, vascular maturation, and immunity. The levels of SGPL1 substrates, S1P, and sphingosine were markedly increased in the patients' blood and fibroblasts, as determined by liquid chromatography-tandem mass spectrometry. Vascular alterations were present in a patient's renal biopsy, in line with changes seen in Sgpl1 knockout mice that are compatible with a developmental defect in vascular maturation. In conclusion, loss of SGPL1 function is associated with CNS, adrenal calcifications, and hypogonadism.

[UTILIZATION OF WHOLE EXOME SEQUENCING IN DIAGNOSTICS OF GENETIC DISEASE: RABIN MEDICAL CENTER'S EXPERIENCE].

INTRODUCTION: Whole exome sequencing is a diagnostic approach for the identification of molecular etiology in patients with suspected monogenic diseases. In this article we report on our experience with whole-exome sequencing (WES) of DNA samples taken from patients referred for genetic evaluation due to suspected undiagnosed genetic conditions. METHODS: Exome enrichment was achieved by Nextera Rapid Capture Expanded Exome Kit. Whole-exome sequencing was performed on Illumina HiSeq 2500. Potentially damaging rare variants were selected for familial cosegregation analysis. RESULTS: A total of 39 patients presenting a wide range of phenotypes suspected to have a genetic cause were sent to WES. Approximately 80% were children with neurological phenotypes. Variations having a high probability of being causative were identified in 20 families, achieving a 51.3% molecular diagnostic rate. Among these, 7 exhibited autosomal dominant disease, 12 autosomal recessive diseases and one X-linked disease; 28% of the patients (11/39) were found to carry a novel mutation located in previously reported genes. Novel mutations located in genes not known to be associated with genetic disease were identified in 23% of the patients (9/39). CONCLUSIONS: Whole exome sequencing identified the underlying genetic cause in more than half of the patients referred for evaluation in the genetics clinic at the tertiary hospital. These data demonstrate the utility of WES as a powerful tool for effective diagnostics of monogenic genetic diseases.

Exome sequencing identified mutations in CASK and MYBPC3 as the cause of a complex dilated cardiomyopathy phenotype.

Whole-exome sequencing for clinical applications is now an integral part of medical genetics practice. Though most studies are performed in order to establish diagnoses in individuals with rare and clinically unrecognizable disorders, due to the constantly decreasing costs and commercial availability, whole-exome sequencing has gradually become the initial tool to study patients with clinically recognized disorders when more than one gene is responsible for the phenotype or in complex phenotypes, when variants in more than one gene can be the cause for the disease. Here we report a patient presenting with a complex phenotype consisting of severe, adult-onset, dilated cardiomyopathy, hearing loss and developmental delay, in which exome sequencing revealed two genetic variants that are inherited from a healthy mother: a novel missense variant in the CASK gene, mutations in which cause a spectrum of neurocognitive manifestations, and a second variant, in MYBPC3, that is associated with hereditary cardiomyopathy. We conclude that although the potential for co-occurrence of rare diseases is higher when analyzing undefined phenotypes in consanguineous families, it should also be given consideration in the genetic evaluation of complex phenotypes in non-consanguineous families.

Exome sequencing identified a novel de novo OPA1 mutation in a consanguineous family presenting with optic atrophy.

Inherited optic neuropathies are a heterogeneous group of disorders characterized by mild to severe visual loss, colour vision deficit, central or paracentral visual field defects and optic disc pallor. Optic atrophies can be classified into isolated or non-syndromic and syndromic forms. While multiple modes of inheritance have been reported, autosomal dominant optic atrophy and mitochondrial inherited Leber's hereditary optic neuropathy are the most common forms. Optic atrophy type 1, caused by mutations in the OPA1 gene is believed to be the most common hereditary optic neuropathy, and most patients inherit a mutation from an affected parent. In this study we used whole-exome sequencing to investigate the genetic aetiology in a patient affected with isolated optic atrophy. Since the proband was the only affected individual in his extended family, and was a product of consanguineous marriage, homozygosity mapping followed by whole-exome sequencing were pursued. Exome results identified a novel de novo OPA1 mutation in the proband. We conclude, that though de novo OPA1 mutations are uncommon, testing of common optic atrophy-associated genes such as mitochondrial mutations and OPA1 gene sequencing should be performed first in single individuals presenting with optic neuropathy, even when dominant inheritance is not apparent.

Possible incipient sympatric ecological speciation in blind mole rats (Spalax).

Sympatric speciation has been controversial since it was first proposed as a mode of speciation. Subterranean blind mole rats (Spalacidae) are considered to speciate allopatrically or peripatrically. Here, we report a possible incipient sympatric adaptive ecological speciation in Spalax galili (2n = 52). The study microsite (0.04 km(2)) is sharply subdivided geologically, edaphically, and ecologically into abutting barrier-free ecologies divergent in rock, soil, and vegetation types. The Pleistocene Alma basalt abuts the Cretaceous Senonian Kerem Ben Zimra chalk. Only 28% of 112 plant species were shared between the soils. We examined mitochondrial DNA in the control region and ATP6 in 28 mole rats from basalt and in 14 from chalk habitats. We also sequenced the complete mtDNA (16,423 bp) of four animals, two from each soil type. Remarkably, the frequency of all major haplotype clusters (HC) was highly soil-biased. HCI and HCII are chalk biased. HC-III was abundant in basalt (36%) but absent in chalk; HC-IV was prevalent in basalt (46.5%) but was low (20%) in chalk. Up to 40% of the mtDNA diversity was edaphically dependent, suggesting constrained gene flow. We identified a homologous recombinant mtDNA in the basalt/chalk studied area. Phenotypically significant divergences differentiate the two populations, inhabiting different soils, in adaptive oxygen consumption and in the amount of outside-nest activity. This identification of a possible incipient sympatric adaptive ecological speciation caused by natural selection indirectly refutes the allopatric alternative. Sympatric ecological speciation may be more prevalent in nature because of abundant and sharply abutting divergent ecologies.

Mutations in TAX1BP3 cause dilated cardiomyopathy with septo-optic dysplasia.

We describe a Bedouin family with a novel autosomal recessive syndrome characterized by dilated cardiomyopathy and septo-optic dysplasia. Genetic analysis revealed a homozygous missense mutation in TAX1BP3, which encodes a small PDZ domain containing protein implicated in regulation of the Wnt/ß-catenin signaling pathway, as the causative mutation. The mutation affects a conserved residue located at the core of TAX1BP3 binding pocket and is predicted to impair the nature of a crucial hydrophobic patch, thereby interrupting the structure and stability of the protein, and its ability to interact with other proteins. TAX1BP3 is highly expressed in heart and brain and consistent with the clinical findings observed in our patients; a knockdown of TAX1BP3 causes elongation defects, enlarged pericard, and enlarged head structures in zebrafish embryos. Thus, we describe a new genetic disorder that expands the monogenic cardiomyopathy disease spectrum and suggests that TAX1BP3 is essential for heart and brain development.

Autosomal recessive lissencephaly with cerebellar hypoplasia is associated with a loss-of-function mutation in CDK5.

Lissencephaly comprises a heterogeneous group of developmental brain disorders of varying severity, involving abnormal cortical gyration. We studied a highly consanguineous Israeli Moslem family with a lethal form of autosomal recessive lissencephaly with cerebellar hypoplasia (LCH). Using microarray-based homozygosity mapping in the reported family, combined with whole exome sequencing in one affected infant, we identified a homozygous splice site mutation g.IVS8+1G>A in cyclin-dependent kinase 5 (CDK5), causing complete skipping of exon 8, and leading to a frame shift and premature stop codon (p.V162SfsX19). The mutation co-segregated with the disease phenotype in all 29 study participants (4 patients and 25 healthy relatives), and was not identified in 200 ethnically matched control chromosomes. The p.V162SfsX19 mutation causes lack of endogenous CDK5 expression in affected dermal fibroblasts and brain tissue at the mRNA and protein levels, consistent with nonsense-mediated mRNA decay. Functional analysis of the p.V162SfsX19 mutation, using a yeast complementation assay, showed loss-of-function of the mutant CDK5 gene product, thereby implicating its role in the pathogenesis of autosomal recessive LCH in the studied family.

Homozygous MED25 mutation implicated in eye-intellectual disability syndrome.

Genetic syndromes involving both brain and eye abnormalities are numerous and include syndromes such as Warburg micro syndrome, Kaufman oculocerebrofacial syndrome, Cerebro-oculo-facio-skeletal syndrome, Kahrizi syndrome and others. Using exome sequencing, we have been able to identify homozygous mutation p.(Tyr39Cys) in MED25 as the cause of a syndrome characterized by eye, brain, cardiac and palatal abnormalities as well as growth retardation, microcephaly and severe intellectual disability in seven patients from four unrelated families, all originating from the same village. The protein encoded by MED25 belongs to Mediator complex or MED complex, which is an evolutionary conserved multi-subunit RNA polymerase II transcriptional regulator complex. The MED25 point mutation is located in the von Willebrand factor type A (MED25 VWA) domain which is responsible for MED25 recruitment into the Mediator complex; co-immunoprecipitation experiment demonstrated that this mutation dramatically impairs MED25 interaction with the Mediator complex in mammalian cells.

A founder effect for p47(phox)Trp193Ter chronic granulomatous disease in Kavkazi Jews.

Chronic granulomatous disease (CGD) is a rare congenital immune deficiency caused by mutations in any of the five genes encoding NADPH oxidase subunits. One of these genes is NCF1, encoding the p47(phox) protein. A group of 39 patients, 14 of whom are of Kavkazi Jewish descent, was investigated for a founder effect for the mutation c.579G>A (p.Trp193Ter) in NCF1. We analyzed various genetic markers in the NCF1 region, including two single nucleotide polymorphisms (SNPs) in NCF1 and two short tandem repeats (STRs) located near NCF1. Most patients were homozygous for the c.579G>A mutation, but three patients were hemizygotes, with a deletion of NCF1 on the other allele, and three patients were compound heterozygotes with another mutation in NCF1. All Kavkazi Jewish patients had a c.295G_c.345T SNP combination in NCF1 and shared a common number of repeats in STR3. In addition, 90% of the Kavkazi Jewish patients shared a common number of repeats in STR1. This uniformity indicates that the c.579G>A mutation in NCF1 was introduced some 1200-2300 years ago in the Kavkazi Jewish population. Variation amongst the other investigated populations from the Middle East indicates that this mutation exists in these non-Kavkazi populations already for more than 5000 years.

Identification of a novel mutation in the PNLIP gene in two brothers with congenital pancreatic lipase deficiency.

Congenital pancreatic lipase (PNLIP) deficiency is a rare monoenzymatic form of exocrine pancreatic failure characterized by decreased absorption of dietary fat and greasy voluminous stools, but apparent normal development and an overall good state of health. While considered to be an autosomal recessive state affecting a few dozens of individuals world-wide and involving the PNLIP gene, no causative mutations for this phenotype were so far reported. Here, we report the identification of the homozygote missense mutation, Thr221Met [c.662C>T], in two brothers from a consanguineous family of Arab ancestry. The observed genotypes among the family members were concordant with an autosomal recessive mode of inheritance but moreover a clear segregation between the genotype state and the serum PNLIP activity was evident. Based on biophysical computational tools, we suggest the mutation disrupts the protein's stability and impairs its normal function. Although the role of PNLIP is well established, our observations provide genetic evidence that PNLIP mutations are causative for this phenotype.