Variable phenotype of a null PPP1R13L allele in children with dilated cardiomyopathy

Childhood-onset cardiomyopathy is a genetically heterogeneous group of conditions with several genes implicated. Recently, biallelic loss-of-function variants in PPP1R13L have been reported in association with a syndromic form of dilated cardiomyopathy (DCM). In addition, affected children manifest skin and hair abnormalities, cleft lip and palate (CLP), and eye findings. Here, we delineate the condition further by describing the phenotype associated with a homozygous frameshift variant (p.Arg330 ProfsTer76) in PPP1R13L detected in two sibships in a consanguineous family with six affected children. The index case had DCM and wooly hair, two of his siblings had DCM and CLP while three cousins had, in addition, glaucoma. Global developmental delay was observed in one child. All the children, except one, died during early childhood. Whole exome sequencing and whole genome sequencing did not reveal any other plausible variant. We provide further evidence that implicates PPP1R13L in a variable syndromic form of severe childhood-onset DCM and suggests expanding the spectrum of this condition to include glaucoma. Given the variability of the phenotype associated with PPP1R13-related DCM, a thorough evaluation of each case is highly recommended even in the presence of an apparently isolated DCM.

Biallelic variants in FLII cause pediatric cardiomyopathy by disrupting cardiomyocyte cell adhesion and myofibril organization

Pediatric cardiomyopathy (CM) represents a group of rare, severe disorders that affect the myocardium. To date, the etiology and mechanisms underlying pediatric CM are incompletely understood, hampering accurate diagnosis and individualized therapy development. Here, we identified biallelic variants in the highly conserved flightless-I (FLII) gene in 3 families with idiopathic, early-onset dilated CM. We demonstrated that patient-specific FLII variants, when brought into the zebrafish genome using CRISPR/Cas9 genome editing, resulted in the manifestation of key aspects of morphological and functional abnormalities of the heart, as observed in our patients. Importantly, using these genetic animal models, complemented with in-depth loss-of-function studies, we provided insights into the function of Flii during ventricular chamber morphogenesis in vivo, including myofibril organization and cardiomyocyte cell adhesion, as well as trabeculation. In addition, we identified Flii function to be important for the regulation of Notch and Hippo signaling, crucial pathways associated with cardiac morphogenesis and function. Taken together, our data provide experimental evidence for a role for FLII in the pathogenesis of pediatric CM and report biallelic variants as a genetic cause of pediatric CM.

Reversible Cardiomyopathy, What Should the Clinicians Keep in Mind? A Case Report

Primary carnitine deficiency (PCD) is an autosomal recessive disorder characterized by decreased carnitine levels essential for Beta oxidation in various organs, including the heart. Early diagnosis and treatment of PCD can revert cardiomyopathy. A 13-year-old girl presented with heart failure due to dilated cardiomyopathy and severe cardiac dysfunction; following L carnitine treatment, the patient's clinical conditions improved, and cardiac functions returned to normal within weeks. Investigations revealed PCD; regular L carnitine has been provided, all cardiac medications are discontinued, and the patient is doing well. We believe PCD should be ruled out in every patient with cardiomyopathy.

Association of Myocardial Muscle Non-Compaction and Multiple Ventricular Septal Defects by Echocardiography

The aim of this study is to examine the possible high association between multiple ventricular septal defect (mVSDs) and noncompaction cardiomyopathy (NCM) as same embryological origin, and the effect of depressed ventricular function in NCM cases during the follow-up, using echocardiography. A total of 150 patients with mVSDs were diagnosed in a single center in Saudi Arabia; 40 cases with isolated or associated with minor congenital heart disease were recruited. Three specialist echocardiography consultants confirmed the NCM diagnosis separately using Jenni, Chin and Patrick criteria, and myocardial function was estimated by ejection fraction at admission and at follow-up after surgery. Stata-14 to analyze the data was used. In our cohort of 40 cases with mVSD (median age at diagnosis = 0.5 years; mean follow-up = 4.84 years), 13(33%) had criteria of non-compaction confirmed by the three specialist consultants. All were operated by surgery and 11 hybrid approach (interventional & surgery). A significant relationship between abnormal trabeculations and mVSD with or without non-compaction was observed, 34% vs 66% respectively (p < 0.03, Fisher's exact test). A repeated-measures t-test found the difference between follow-up and preoperative ejection-fractions to be statistically significant (t (39) = 2.07, p < 0.04). Further, the myocardial function in the mVSD non-compaction group normalized substantially postoperatively compared with preoperative assessment (mean difference (MD) 11.77, 95% CI: 4.40-19.14), whilst the mVSD group with normal myocardium had no significant change in the myocardium function (MD 0.74, 95% CI: -4.10-5.58). Thus, treatment outcome appears better in the mVSD non-compaction group than their peers with normal myocardium. Acknowledging the lack of genetic data, it is evident the high incidence of non-compaction in this cohort of patients with mVSD and supports our hypothesis of embryonic/genetic link, unlikely to be explained by acquired cardiomyopathy.

Hypomorphic GINS3 variants alter DNA replication and cause Meier-Gorlin syndrome

The eukaryotic CDC45/MCM2-7/GINS (CMG) helicase unwinds the DNA double helix during DNA replication. The GINS subcomplex is required for helicase activity and is, therefore, essential for DNA replication and cell viability. Here, we report the identification of 7 individuals from 5 unrelated families presenting with a Meier-Gorlin syndrome–like (MGS-like) phenotype associated with hypomorphic variants of GINS3, a gene not previously associated with this syndrome. We found that MGS-associated GINS3 variants affecting aspartic acid 24 (D24) compromised cell proliferation and caused accumulation of cells in S phase. These variants shortened the protein half-life, altered key protein interactions at the replisome, and negatively influenced DNA replication fork progression. Yeast expressing MGS-associated variants of PSF3 (the yeast GINS3 ortholog) also displayed impaired growth, S phase progression defects, and decreased Psf3 protein stability. We further showed that mouse embryos homozygous for a D24 variant presented intrauterine growth retardation and did not survive to birth, and that fibroblasts derived from these embryos displayed accelerated cellular senescence. Taken together, our findings implicate GINS3 in the pathogenesis of MGS and support the notion that hypomorphic variants identified in this gene impaired cell and organismal growth by compromising DNA replication.

A complex unit for a complex disease: the HCM-Family Unit

Hypertrophic cardiomyopathy (HCM) is a group of heterogeneous disorders that are most commonly passed on in a heritable manner. It is a relatively rare disease around the globe, but due to increased rates of consanguinity within the Kingdom of Saudi Arabia, we speculate a high incidence of undiagnosed cases. The aim of this paper is to elucidate a systematic approach in dealing with HCM patients and since HCM has variable presentation, we have summarized differentials for diagnosis and how different subtypes and genes can have an impact on the clinical picture, management and prognosis. Moreover, we propose a referral multi-disciplinary team HCM-Family Unit in Saudi Arabia and an integrated role in a network between King Faisal Hospital and Inherited and Rare Cardiovascular Disease Unit-Monaldi Hospital, Italy (among the 24 excellence centers of the European Reference Network (ERN) GUARD-Heart).   Graphical Abstract.

Pulmonary arteriovenous malformation with unexplained cyanosis as the first presentation of hereditary haemorrhagic telangiectasia, case report, and literature review

Background

Pulmonary arteriovenous malformations (PAVMs) are rare pulmonary vascular anomalies. They can result in right-to-left shunt and, if significant, low systemic saturation, cyanosis, polycythaemia, and paradoxical systemic embolization.

Case summary

Eighteen months old female child was referred to our centre due to unexplained central and peripheral cyanosis. Based on the agitated saline contrast echocardiography study, computed tomography scan confirmed the presence of abnormal vasculature at the left lower lobe. Percutaneous closure of the PAVM was performed using Amplatzer Duct Occluder type 1 device. The genetic study revealed a pathogenic mutation in the endoglin gene, which is a known cause of hereditary haemorrhagic telangiectasia (HHT) inhered in an autosomal dominance pattern.

Discussion

PAVM could be the first manifestation of HHT. Closing the malformation percutaneously is feasible, which can eliminate the right to left shunt and improves the saturation. Genetic study is warranted in these cases, as well as long-term follow-up.

A human importin-β-related disorder: Syndromic thoracic aortic aneurysm caused by bi-allelic loss-of-function variants in IPO8

Importin 8, encoded by IPO8, is a ubiquitously expressed member of the importin-β protein family that translocates cargo molecules such as proteins, RNAs, and ribonucleoprotein complexes into the nucleus in a RanGTP-dependent manner. Current knowledge of the cargoes of importin 8 is limited, but TGF-β signaling components such as SMAD1-4 have been suggested to be among them. Here, we report that bi-allelic loss-of-function variants in IPO8 cause a syndromic form of thoracic aortic aneurysm (TAA) with clinical overlap with Loeys-Dietz and Shprintzen-Goldberg syndromes. Seven individuals from six unrelated families showed a consistent phenotype with early-onset TAA, motor developmental delay, connective tissue findings, and craniofacial dysmorphic features. A C57BL/6N Ipo8 knockout mouse model recapitulates TAA development from 8-12 weeks onward in both sexes but most prominently shows ascending aorta dilatation with a propensity for dissection in males. Compliance assays suggest augmented passive stiffness of the ascending aorta in male Ipo8^-/- mice throughout life. Immunohistological investigation of mutant aortic walls reveals elastic fiber disorganization and fragmentation along with a signature of increased TGF-β signaling, as evidenced by nuclear pSmad2 accumulation. RT-qPCR assays of the aortic wall in male Ipo8^-/- mice demonstrate decreased Smad6/7 and increased Mmp2 and Ccn2 (Ctgf) expression, reinforcing a role for dysregulation of the TGF-β signaling pathway in TAA development. Because importin 8 is the most downstream TGF-β-related effector implicated in TAA pathogenesis so far, it offers opportunities for future mechanistic studies and represents a candidate drug target for TAA.

Calmodulin mutations and life-threatening cardiac arrhythmias: insights from the International Calmodulinopathy Registry

AIMS

Calmodulinopathies are rare life-threatening arrhythmia syndromes which affect mostly young individuals and are, caused by mutations in any of the three genes (CALM 1-3) that encode identical calmodulin proteins. We established the International Calmodulinopathy Registry (ICalmR) to understand the natural history, clinical features, and response to therapy of patients with a CALM-mediated arrhythmia syndrome.

METHODS AND RESULTS

A dedicated Case Report File was created to collect demographic, clinical, and genetic information. ICalmR has enrolled 74 subjects, with a variant in the CALM1 (n = 36), CALM2 (n = 23), or CALM3 (n = 15) genes. Sixty-four (86.5%) were symptomatic and the 10-year cumulative mortality was 27%. The two prevalent phenotypes are long QT syndrome (LQTS; CALM-LQTS, n = 36, 49%) and catecholaminergic polymorphic ventricular tachycardia (CPVT; CALM-CPVT, n = 21, 28%). CALM-LQTS patients have extremely prolonged QTc intervals (594 ± 73 ms), high prevalence (78%) of life-threatening arrhythmias with median age at onset of 1.5 years [interquartile range (IQR) 0.1-5.5 years] and poor response to therapies. Most electrocardiograms (ECGs) show late onset peaked T waves. All CALM-CPVT patients were symptomatic with median age of onset of 6.0 years (IQR 3.0-8.5 years). Basal ECG frequently shows prominent U waves. Other CALM-related phenotypes are idiopathic ventricular fibrillation (IVF, n = 7), sudden unexplained death (SUD, n = 4), overlapping features of CPVT/LQTS (n = 3), and predominant neurological phenotype (n = 1). Cardiac structural abnormalities and neurological features were present in 18 and 13 patients, respectively.

CONCLUSION

Calmodulinopathies are largely characterized by adrenergically-induced life-threatening arrhythmias. Available therapies are disquietingly insufficient, especially in CALM-LQTS. Combination therapy with drugs, sympathectomy, and devices should be considered.

A novel homozygous SCN5A variant detected in sick sinus syndrome

Sick sinus syndrome (SSS) is a group of disorders characterized by an abnormal cardiac impulse formation or propagation from the sinoatrial node. Mutated SCN5A has been reported in SSS, however, homozygosity of SCN5A is exceedingly rare. Here, we report a consanguineous family with four affected children with SSS. Symptomatic bradycardia necessitated implanting a pacemaker in all of them. Sequencing SCN5A revealed a novel homozygous variant (p.Cys1850Arg), which was predicted to interfere with protein folding. Our report describes the phenotype of a novel homozygous SCN5A variant and contributes to the compendium of molecular pathology of inherited arrhythmias in consanguineous populations.

Categorized Genetic Analysis in Childhood-Onset Cardiomyopathy

BACKGROUND

Childhood-onset cardiomyopathy is a heterogeneous group of conditions the cause of which is largely unknown. The influence of consanguinity on the genetics of cardiomyopathy has not been addressed at a large scale.

METHODS

To unravel the genetic cause of childhood-onset cardiomyopathy in a consanguineous population, a categorized approach was adopted. Cases with childhood-onset cardiomyopathy were consecutively recruited. Based on the likelihood of founder mutation and on the clinical diagnosis, genetic test was categorized to either (1) targeted genetic test with targeted mutation test, single-gene test, or multigene panel for Noonan syndrome, or (2) untargeted genetic test with whole-exome sequencing or whole-genome sequencing. Several bioinformatics tools were used to filter the variants.

RESULTS

Two-hundred five unrelated probands with various forms of cardiomyopathy were evaluated. The median age of presentation was 10 months. In 30.2% (n=62), targeted genetic test had a yield of 82.7% compared with 33.6% for whole-exome sequencing/whole-genome sequencing (n=143) giving an overall yield of 53.7%. Strikingly, 96.4% of the variants were homozygous, 9% of which were found in 4 dominant genes. Homozygous variants were also detected in 7 novel candidates (ACACB, AASDH, CASZ1, FLII, RHBDF1, RPL3L, ULK1).

CONCLUSIONS

Our work demonstrates the impact of consanguinity on the genetics of childhood-onset cardiomyopathy, the value of adopting a categorized population-sensitive genetic approach, and the opportunity of uncovering novel genes. Our data suggest that if a founder mutation is not suspected, adopting whole-exome sequencing/whole-genome sequencing as a first-line test should be considered.

Genetic Mosaicism in Calmodulinopathy

BACKGROUND

CaM (calmodulin) mutations are associated with congenital arrhythmia susceptibility (calmodulinopathy) and are most often de novo. In this report, we sought to broaden the genotype-phenotype spectrum of calmodulinopathies with 2 novel calmodulin mutations and to investigate mosaicism in 2 affected families.

METHODS

CaM mutations were identified in 4 independent cases by DNA sequencing. Biochemical and electrophysiological studies were performed to determine functional consequences of each mutation.

RESULTS

Genetic studies identified 2 novel CaM variants (CALM3-E141K in 2 cases; CALM1-E141V) and one previously reported CaM pathogenic variant (CALM3-D130G) among 4 probands with shared clinical features of prolonged QTc interval (range 505-725 ms) and documented ventricular arrhythmia. A fatal outcome occurred for 2 of the cases. The parents of all probands were asymptomatic with normal QTc duration. However, 2 of the families had multiple affected offspring or multiple occurrences of intrauterine fetal demise. The mother from the family with recurrent intrauterine fetal demise exhibited the CALM3-E141K mutant allele in 25% of next-generation sequencing reads indicating somatic mosaicism, whereas CALM3-D130G was present in 6% of captured molecules of the paternal DNA sample, also indicating mosaicism. Two novel mutations (E141K and E141V) impaired Ca²⁺ binding affinity to the C-domain of CaM. Human-induced pluripotent stem cell-derived cardiomyocytes overexpressing mutant or wild-type CaM showed that both mutants impaired Ca²⁺-dependent inactivation of L-type Ca²⁺ channels and prolonged action potential duration.

CONCLUSIONS

We report 2 families with somatic mosaicism associated with arrhythmogenic calmodulinopathy, and demonstrate dysregulation of L-type Ca²⁺ channels by 2 novel CaM mutations affecting the same residue. Parental mosaicism should be suspected in families with unexplained fetal arrhythmia or fetal demise combined with a documented CaM mutation.

Phenotypic variability in a series of four pediatric patients with Andersen-Tawil syndrome: A Saudi experience

Andersen-Tawil syndrome (ATS) is a rare genetic disorder characterized by periodic paralysis, ventricular arrhythmia, and dysmorphic features. However, the classical features are not always seen in the syndrome; therefore, the diagnosis can be challenging. We describe our experience with ATS in Riyadh, Saudi Arabia, by presenting a case series involving four patients in the pediatric cardiology clinic confirmed to have ATS. Despite the diversity in phenotypes and clinical course among the four cases, all patients had bidirectional ventricular tachycardia and were confirmed to have ATS by performing genetic testing. In this case series, we identified one novel and three previously described KCNJ2 mutations. We also confirmed the beneficial effect of AAI pacing in one of our patients, together with medical therapy with β-blockers and flecainide. In Saudi Arabia, there is a distinct genetic pool and a high incidence of inherited diseases. Raising awareness about these diseases is crucial, especially in a country such as Saudi Arabia, wherein consanguinity remains a significant factor leading to an increased incidence of inherited diseases. Furthermore, because of the limited information available regarding this rare syndrome, we believe that this case series would offer an opportunity to provide a better understanding of ATS in our local region and worldwide.

Rubinstein-Taybi syndrome in a Saudi boy with distinct features and variants in both the CREBBP and EP300 genes: a case report

BACKGROUND

Rubinstein-Taybi syndrome (RSTS) Type 1 (OMIM 180849) is characterized by three main features: intellectual disability; broad and frequently angulated thumbs and halluces; and characteristic facial dysmorphism.

CASE PRESENTATION

We report on a Saudi boy with RSTS Type 1 and the following distinct features: a midline notch of the upper lip, a bifid tip of the tongue, a midline groove of the lower lip, plump fingers with broad / flat fingertips, and brachydactyly. The child was found to be heterozygous in the CREBBP gene for a sequence variant designated c.4963del, which is predicted to result in premature protein termination p.Leu1655Cysfs*89. The child and his father were also found to be heterozygous in the EP300 gene for a sequence variant designated c.586A > G, which is predicted to result in the amino-acid substitution p.Ile196Val.

CONCLUSION

Our report expands the clinical spectrum of RSTS to include several distinct facial and limb features. The variant of the CREBBP gene is known to be causative of RSTS Type 1. The variant in the EP300 gene is benign since the father carried the same variant and exhibited no abnormalities. However, functional studies are required to investigate if this benign EP300 variant influences the phenotype in the presence of disease-causing CREBBP gene mutations.

The many faces of peroxisomal disorders: Lessons from a large Arab cohort

Defects in the peroxisomes biogenesis and/or function result in peroxisomal disorders. In this study, we describe the largest Arab cohort to date (72 families) of clinically, biochemically and molecularly characterized patients with peroxisomal disorders. At the molecular level, we identified 43 disease-causing variants, half of which are novel. The founder nature of many of the variants allowed us to calculate the minimum disease burden for these disorders in our population ~1:30 000, which is much higher than previous estimates in other populations. Clinically, we found an interesting trend toward genotype/phenotype correlation in terms of long-term survival. Nearly half (40/75) of our peroxisomal disorders patients had documented survival beyond 1 year of age. Most unusual among the long-term survivors was a multiplex family in which the affected members presented as adults with non-specific intellectual disability and epilepsy. Other unusual presentations included the very recently described peroxisomal fatty acyl-CoA reductase 1 disorder as well as CRD, spastic paraparesis, white matter (CRSPW) syndrome. We conclude that peroxisomal disorders are highly heterogeneous in their clinical presentation. Our data also confirm the demonstration that milder forms of Zellweger spectrum disorders cannot be ruled out by the "gold standard" very long chain fatty acids assay, which highlights the value of a genomics-first approach in these cases.

Modifying inter-cistronic sequence significantly enhances IRES dependent second gene expression in bicistronic vector: Construction of optimised cassette for gene therapy of familial hypercholesterolemia

Internal ribosome entry site (IRES) sequences have become a valuable tool in the construction of gene transfer and therapeutic vectors for multi-cistronic gene expression from a single mRNA transcript. The optimal conditions for effective use of this sequence to construct a functional expression vector are not precisely defined but it is generally assumed that the internal ribosome entry site dependent expression of the second gene in such as cassette is less efficient than the cap-dependent expression of the first gene. Mainly tailoring inter-cistronic sequence significantly enhances IRES dependent second gene expression in bicistronic vector further in construction of optimised cassette for gene therapy of familial hypercholesterolemia. We tailored the size of the inter-cistronic spacer sequence at the 5′ region of the internal ribosome entry site sequence using sequential deletions and demonstrated that the expression of the 3′ gene can be significantly increased to similar levels as the cap-dependent expression of the 5’ gene. Maximum expression efficiency of the downstream gene was obtained when the spacer is composed of 18–141 base pairs. In this case a single mRNA transcriptional unit containing both the first and the second Cistron was detected. Whilst constructs with spacer sequences of 216 bp or longer generate a single transcriptional unit containing only the first Cistron. This suggests that long spacers may affect transcription termination. When the spacer is 188 bp, both transcripts were produced simultaneously in most transfected cells, while a fraction of them expressed only the first but not the second gene. Expression analyses of vectors containing optimised cassettes clearly confirm that efficiency of gene transfer and biological activity of the expressed transgenic proteins in the transduced cells can be achieved. Furthermore, Computational analysis was carried out by molecular dynamics (MD) simulation to determine the most emerges as viable containing specific binding site and bridging of 5′ and 3′ ends involving direct RNA-RNA contacts and RNA-protein interactions. These results provide a mechanistic basis for translation stimulation and RNA resembling for the synergistic stimulation of cap-dependent translation.

Further delineation of Temtamy syndrome of corpus callosum and ocular abnormalities

Temtamy syndrome is a syndromic form of intellectual disability characterized by ocular involvement, epilepsy and dysgenesis of the corpus callosum. After we initially mapped the disease to C12orf57, we noted a high carrier frequency of an ancient startloss founder mutation [c.1A>G; p.M1?] in our population, and variable phenotypic expressivity in newly identified cases. This study aims to combine 33 previously published patients with 23 who are described here for the first time to further delineate the phenotype of this syndrome. In addition to the known p.M1? founder, we describe four novel homozygous variants, thus increasing the number of Temtamy syndrome-related C12orf57 variants to seven, all but one predicted to be loss of function. While all patients presented with intellectual disability/developmental delay, the frequency of other phenotypic features was variable: 73.2% (41/56) had epilepsy, 63% (34/54) had corpus callosal abnormalities, 14.5% (8/55) had coloboma, and 16.4% (9/55) had microphthalmia. Our analysis also revealed a high frequency of less recognized features such as congenital heart disease (51.4%), and brain white matter abnormalities (38%, 19/50). We conclude that C12orf57 variants should be considered in the etiology of developmental delay/intellectual disability, even when typical syndromic features are lacking, especially in those who trace their ancestry to Saudi Arabia where a founder C12orf57 mutation is among the most common recessive causes of intellectual disability.

The Phenotype and Outcome of Infantile Cardiomyopathy Caused by a Homozygous ELAC2 Mutation

OBJECTIVE

Cardiomyopathy (CMP) in children is a clinically and genetically heterogeneous group of disorders. Disease-associated mutations have been identified in more than 50 genes. Recently, mutations in the mitochondrial tRNA processing gene, ELAC2, were reported to be associated with the recessively inherited form of hypertrophic CMP (HCM). This study is aimed at describing the cardiac phenotype and outcome of ELAC2 mutation.

METHODS

We performed whole exome sequencing followed by targeted mutation screening to identify the genetic etiology of severe infantile-onset CMP in 64 consanguineous Saudi families.

RESULTS

A previously reported mutation (p.Phe154Leu) in ELAC2 gene was detected in 16 families. The index cases presented between 2 and 7 months of age with HCM in 13 infants and dilated CMP (DCM) in 3. Pericardial effusion was observed in 7 infants (44%). All infants died with a median age of death of 4 months. Almost 1/3 of them died during the initial presentation.

CONCLUSION

Our study suggests screening the ELAC2 gene in severe infantile-onset HCM or DCM of unknown etiology, especially in the presence of pericardial effusion. Our work demonstrates a universally poor outcome of the (p.Phe154Leu) variant in ELAC2 gene; a correlation that helps in counseling parents and in planning appropriate medical intervention.

Clinical profile and mutation spectrum of long QT syndrome in Saudi Arabia: The impact of consanguinity

BACKGROUND

Congenital long QT syndrome (LQTS) is an inherited, potentially fatal arrhythmogenic disorder. At least 16 genes have been implicated in LQTS; the yield of genetic analysis of 3 genes (KCNQ1, KCNH2, and SCN5A) is about 70%, with KCNQ1 mutations accounting for ∼50% of positive cases. LQTS is mostly inherited in an autosomal dominant pattern. Systemic analysis of LQTS has not been previously conducted in a population with a high degree of consanguinity.

OBJECTIVES

To describe the clinical and molecular profiles of LQTS in the highly consanguineous Saudi population.

METHODS

Fifty-six Saudi families with LQTS were consecutively recruited and evaluated. Sequencing of KCNQ1, KCNH2, and SCN5A genes was conducted on all probands, followed by screening of family relatives.

RESULTS

Genetic analysis was positive in 32 (57.2%) families, with mutations in KCNQ1 identified in 28 families (50%). Surprisingly, 17 (53.1%) probands were segregating homozygous mutations. Family screening identified 123 individuals with mutations; 89 (72.4%) were heterozygous, 23 (18.7%) were homozygous, and 11 (8.9%) were compound heterozygous. Compared to heterozygous, the phenotype was more severe in homozygous individuals, with cardiac symptoms in 78.3% (vs 12.4%), family history of sudden death in 64.7% (vs 44.4%), and prolonged QT interval in 100% (vs 43.8%). Congenital deafness was found in 11 (47.8%) homozygous probands.

CONCLUSION

Our study provides insight into the clinical and molecular profiles of LQTS in a consanguineous population. It underscores the importance of preemptive management in homozygous patients with LQTS and the value of clinical and molecular screening of at-risk relatives.

Clinical genomics expands the morbid genome of intellectual disability and offers a high diagnostic yield

Intellectual disability (ID) is a measurable phenotypic consequence of genetic and environmental factors. In this study, we prospectively assessed the diagnostic yield of genomic tools (molecular karyotyping, multi-gene panel and exome sequencing) in a cohort of 337 ID subjects as a first-tier test and compared it with a standard clinical evaluation performed in parallel. Standard clinical evaluation suggested a diagnosis in 16% of cases (54/337) but only 70% of these (38/54) were subsequently confirmed. On the other hand, the genomic approach revealed a likely diagnosis in 58% (n=196). These included copy number variants in 14% (n=54, 15% are novel), and point mutations revealed by multi-gene panel and exome sequencing in the remaining 43% (1% were found to have Fragile-X). The identified point mutations were mostly recessive (n=117, 81%), consistent with the high consanguinity of the study cohort, but also X-linked (n=8, 6%) and de novo dominant (n=19, 13%). When applied directly on all cases with negative molecular karyotyping, the diagnostic yield of exome sequencing was 60% (77/129). Exome sequencing also identified likely pathogenic variants in three novel candidate genes (DENND5A, NEMF and DNHD1) each of which harbored independent homozygous mutations in patients with overlapping phenotypes. In addition, exome sequencing revealed de novo and recessive variants in 32 genes (MAMDC2, TUBAL3, CPNE6, KLHL24, USP2, PIP5K1A, UBE4A, TP53TG5, ATOH1, C16ORF90, SLC39A14, TRERF1, RGL1, CDH11, SYDE2, HIRA, FEZF2, PROCA1, PIANP, PLK2, QRFPR, AP3B2, NUDT2, UFC1, BTN3A2, TADA1, ARFGEF3, FAM160B1, ZMYM5, SLC45A1, ARHGAP33 and CAPS2), which we highlight as potential candidates on the basis of several lines of evidence, and one of these genes (SLC39A14) was biallelically inactivated in a potentially treatable form of hypermanganesemia and neurodegeneration. Finally, likely causal variants in previously published candidate genes were identified (ASTN1, HELZ, THOC6, WDR45B, ADRA2B and CLIP1), thus supporting their involvement in ID pathogenesis. Our results expand the morbid genome of ID and support the adoption of genomics as a first-tier test for individuals with ID.

Guidelines for acute management of hyperammonemia in the Middle East region

Background

Hyperammonemia is a life-threatening event that can occur at any age. If treated, the early symptoms in all age groups could be reversible. If untreated, hyperammonemia could be toxic and cause irreversible brain damage to the developing brain.

Objective

There are major challenges that worsen the outcome of hyperammonemic individuals in the Middle East. These include: lack of awareness among emergency department physicians about proper management of hyperammonemia, strained communication between physicians at primary, secondary, and tertiary hospitals, and shortage of the medications used in the acute management of hyperammonemia. Therefore, the urge to develop regional guidelines is extremely obvious.

Method

We searched PubMed and Embase databases to include published materials from 2011 to 2014 that were not covered by the European guidelines, which was published in 2012. We followed the process of a Delphi conference and involved one preliminary meeting and two follow-up meetings with email exchanges between the Middle East Hyperammonemia and Urea Cycle Disorders Scientific Group regarding each draft of the manuscript.

Results and discussion

We have developed consensus guidelines based on the highest available level of evidence. The aim of these guidelines is to homogenize and harmonize the treatment protocols used for patients with acute hyperammonemia, and to provide a resource to not only metabolic physicians, but also physicians who may come in contact with individuals with acute hyperammonemia.

Conclusion

These suggested guidelines aim to ease the challenges faced by physicians dealing with acute hyperammonemia in the region. In addition, guidelines have demonstrated useful collaboration between experts in the region, and provides information that will hopefully improve the outcomes of patients with acute hyperammonemia.

A substitution mutation in cardiac ubiquitin ligase, FBXO32, is associated with an autosomal recessive form of dilated cardiomyopathy

Background

Familial dilated cardiomyopathy (DCM) is genetically heterogeneous. Mutations in more than 40 genes have been identified in familial cases, mostly inherited in an autosomal dominant pattern. DCM due to recessive mutations is rarely observed. In consanguineous families, homozygosity mapping and whole exome sequencing (WES) can be utilized to identify the genetic defects in recessively inherited DCM.

Methods

In a consanguineous family with four affected siblings with severe DCM, we combined homozygosity mapping, linkage analysis and WES, to uncover the genetic defect.

Results

A region of homozygosity (ROH) on chromosome 8q24.13–24.23 was found to be shared by all of the four affected siblings. WES detected ~47,000 variants that were filtered to a homozygous mutation (p.Gly243Arg) in the FBXO32 gene, located within the identified ROH. The mutation segregated with the phenotype, replaced a highly-conserved amino acid, and was not detected in 1986 ethnically-matched chromosomes. FBXO32, which encodes a muscle-specific ubiquitin ligase, has been implicated in the pathogenesis of cardiomyopathy through the ubiquitin proteasome system (UPS). In addition, FBXO32-knockout mice manifest with cardiomyopathy. Screening the index patient for all of the WES variants in 48 genes known to be implicated in hypertrophic and dilated cardiomyopathy was negative.

Conclusions

Our data suggest that FBXO32 is a candidate gene for recessive DCM. Acting as a cardiac ubiquitin ligase, mutated FBXO32 could perturb the degradation of target proteins in the UPS, the impairment of which has been observed in cardiomyopathy. Our work proposes that genes encoding other ubiquitin ligases could also be implicated in familial cardiomyopathy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-016-0267-5) contains supplementary material, which is available to authorized users.

Accelerating novel candidate gene discovery in neurogenetic disorders via whole-exome sequencing of prescreened multiplex consanguineous families

Our knowledge of disease genes in neurological disorders is incomplete. With the aim of closing this gap, we performed whole-exome sequencing on 143 multiplex consanguineous families in whom known disease genes had been excluded by autozygosity mapping and candidate gene analysis. This prescreening step led to the identification of 69 recessive genes not previously associated with disease, of which 33 are here described (SPDL1, TUBA3E, INO80, NID1, TSEN15, DMBX1, CLHC1, C12orf4, WDR93, ST7, MATN4, SEC24D, PCDHB4, PTPN23, TAF6, TBCK, FAM177A1, KIAA1109, MTSS1L, XIRP1, KCTD3, CHAF1B, ARV1, ISCA2, PTRH2, GEMIN4, MYOCD, PDPR, DPH1, NUP107, TMEM92, EPB41L4A, and FAM120AOS). We also encountered instances in which the phenotype departed significantly from the established clinical presentation of a known disease gene. Overall, a likely causal mutation was identified in >73% of our cases. This study contributes to the global effort toward a full compendium of disease genes affecting brain function.

Genomic analysis of primordial dwarfism reveals novel disease genes

Primordial dwarfism (PD) is a disease in which severely impaired fetal growth persists throughout postnatal development and results in stunted adult size. The condition is highly heterogeneous clinically, but the use of certain phenotypic aspects such as head circumference and facial appearance has proven helpful in defining clinical subgroups. In this study, we present the results of clinical and genomic characterization of 16 new patients in whom a broad definition of PD was used (e.g., 3M syndrome was included). We report a novel PD syndrome with distinct facies in two unrelated patients, each with a different homozygous truncating mutation in CRIPT. Our analysis also reveals, in addition to mutations in known PD disease genes, the first instance of biallelic truncating BRCA2 mutation causing PD with normal bone marrow analysis. In addition, we have identified a novel locus for Seckel syndrome based on a consanguineous multiplex family and identified a homozygous truncating mutation in DNA2 as the likely cause. An additional novel PD disease candidate gene XRCC4 was identified by autozygome/exome analysis, and the knockout mouse phenotype is highly compatible with PD. Thus, we add a number of novel genes to the growing list of PD-linked genes, including one which we show to be linked to a novel PD syndrome with a distinct facial appearance. PD is extremely heterogeneous genetically and clinically, and genomic tools are often required to reach a molecular diagnosis.

Infantile-onset ascending hereditary spastic paraplegia with bulbar involvement due to the novel ALS2 mutation c.2761C>T

Recessive mutations in the alsin gene cause three clinically distinct motor neuron diseases: juvenile amyotrophic lateral sclerosis (ALS2), juvenile primary lateral sclerosis (JPLS) and infantile-onset ascending hereditary spastic paraplegia (IAHSP). A total of 23 different ALS2 mutations have been described for the three disorders so far. Most of these mutations result in a frameshift leading to a premature truncation of the alsin protein. We report the novel ALS2 truncating mutation c.2761C>T; p.R921X detected by homozygosity mapping and sequencing in two infants affected by IAHSP with bulbar involvement. The mutation c.2761C>T resides in the pleckstrin domain, a characteristic segment of guanine nucleotide exchange factors of the Rho GTPase family, which is involved in the overall neuronal development or maintenance. This study highlights the importance of using homozygosity mapping combined with candidate gene analysis to identify the underlying genetic defect as in this Saudi consanguineous family.

Autozygome-guided exome sequencing in retinal dystrophy patients reveals pathogenetic mutations and novel candidate disease genes

Retinal dystrophy (RD) is a heterogeneous group of hereditary diseases caused by loss of photoreceptor function and contributes significantly to the etiology of blindness globally but especially in the industrialized world. The extreme locus and allelic heterogeneity of these disorders poses a major diagnostic challenge and often impedes the ability to provide a molecular diagnosis that can inform counseling and gene-specific treatment strategies. In a large cohort of nearly 150 RD families, we used genomic approaches in the form of autozygome-guided mutation analysis and exome sequencing to identify the likely causative genetic lesion in the majority of cases. Additionally, our study revealed six novel candidate disease genes (C21orf2, EMC1, KIAA1549, GPR125, ACBD5, and DTHD1), two of which (ACBD5 and DTHD1) were observed in the context of syndromic forms of RD that are described for the first time.

A novel splice site mutation in ERLIN2 causes hereditary spastic paraplegia in a Saudi family

Hereditary Spastic Paraplegias (HSP) encompass a clinically and genetically heterogeneous group of neurodegenerative disorders characterized by insidiously progressive weakness and spasticity of the lower extremities. We describe a consanguineous Saudi family segregating a complicated form of HSP in an autosomal recessive pattern. The two affected siblings had early onset, cognitive, speech and motor involvement with spasticity of the lower extremities. Their upper extremities were mildly hypertonic. An intronic splice acceptor site mutation in ERLIN2 was found to be responsible for causing this disorder found in this family. ERLIN2 is a mediator of endoplasmic reticulum degradation pathway (ERAD) which helps to remove the aberrant proteins. Our results, in concurrence with previous studies suggest that alteration in ERLIN2 is one of the causes of complicated HSP, thereby increasing the spectrum of known mutations in SPG18.

Identification of a novel KCNQ1 mutation in a large Saudi family with long QT syndrome: clinical consequences and preventive implications

Congenital long QT syndrome (LQTS) is an inherited potentially fatal arrhythmogenic disorder that is characterized by prolonged corrected QT (QTc) interval. Mutations in three genes (KCNQ1, KCNH2, and SCN5A) account for the majority of the cases. However, 10 other genes are now known to be implicated in LQTS. In this work, we describe the clinical and molecular analysis in a large Saudi family with LQTS. Screening KCNQ1, KCNH2, and SCN5A genes in the proband, who presented with syncope, led to the identification of a heterozygous mutation (p.H258P) in KCNQ1. An extended clinical and genetic screening of the family identified 11 other members who were carriers for this mutation. All identified carriers had prolonged QTc intervals; yet, only two were symptomatic. Screening the family members for three LQTS modifiers (rs4657139 and rs16847548 in NOS1AP and KCNE1-D85N) did not reveal a correlation with symptoms or QTc intervals. The electrocardiographic and molecular analysis stratified seven carriers at high risk of a cardiac event as they had a QTc of ≥500 ms and were carriers of a KCNQ1 mutation. Our work illustrates the importance of extended family screening in LQTS to identify silent carriers and hence adopt the most appropriate therapeutic and preventive intervention.

Recessively inherited severe aortic aneurysm caused by mutated EFEMP2

Familial aortic aneurysm (AA) is mostly inherited as an autosomal dominant disorder. However, recessively inherited AA has also been observed but in association with skin manifestations of cutis laxa, which is caused by a mutated EFEMP2 gene. In the present study, we recruited 9 patients, from 4 unrelated consanguineous families, with recessively inherited AA. The index cases, their parents, and siblings underwent clinical evaluation and cardiac imaging. In the affected subjects, the clinical presentation ranged from sweating and cyanosis at 3 months of age to incidental findings in an asymptomatic adult. The echocardiogram revealed a wide spectrum of severity of the AA, with a Z-score varying from 5 to 33. Intrafamilial variability was also evident; 2 unrelated subjects were detected at 17 and 20 years of age through family screening. The skin manifestations of cutis laxa were not found in any patient. In 1 family, genome-wide single-nucleotide polymorphism analysis detected a homozygous block, shared by 2 affected siblings, on chromosome 11 at q13. Sequence analysis of EFEMP2, located on chromosome 11 at q13, identified a novel homozygous mutation (p.E161K) in all 9 affected subjects. In this largest cohort of reported patients with a mutated EFEMP2 gene, we illustrate the phenotypic spectrum of inherited AA due to a novel EFEMP2 mutation. In conclusion, our work suggests that in families with apparently recessively inherited AA, molecular analysis of EFEMP2 gene might be warranted.

The phenotype of a CASQ2 mutation in a Saudi family with catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) manifests with episodic syncope or sudden death in young patients following physical activity or emotional stress. The autosomal recessive form of CPVT is caused by mutations in the CASQ2 gene. In a consanguineous family, a novel homozygous CASQ2 mutation (p.L77P) was identified in a child with CPVT who required implantation of a cardioverter defibrillator due to episodes of syncope while on medical therapy. Genetic testing found the younger sibling, who had normal initial clinical screening, to be affected. Our cases underscore the importance of family screening through genetic testing to preemptively apply the appropriate medical intervention in CPVT.

Novel V97G ASAH1 mutation found in Farber disease patients: unique appearance of the disease with an intermediate severity, and marked early involvement of central and peripheral nervous system

Farber disease is a rare inherited lysosomal storage disorder caused by ceramidase deficiency that leads to accumulation of ceramide in various tissues. Mutations within ASAH1 encoding for acid ceramidase are responsible for the disease. Here we report two siblings with Farber disease who carry a novel V97G with the parents and a sister being asymptomatic carriers. The mutation site was found to be highly conserved among different species using ClustalW2 alignment. Functional prediction tools indicated the mutation to be pathogenic. Electron microscopy based ultrastructural studies using skin biopsy showed inclusion of enlarged lysosomes and presence of the zebra bodies. The T1 weighted magnetic resonance images of the brain indicated diffuse loss of the deep white matter volume predominantly along the occipital horns of the lateral ventricle with subsequent facet dilatation of the supratentorial and infratentorial ventricular system. This is the first report of a detailed clinical and molecular analysis of cases with Farber disease from Saudi Arabia.

Clinical, biochemical and molecular characterization of peroxisomal diseases in Arabs

Peroxisomes are single membrane-bound cellular organelles that carry out critical metabolic reactions perturbation of which leads to an array of clinical phenotypes known as peroxisomal disorders (PD). In this study, the largest of its kind in the Middle East, we sought to comprehensively characterize these rare disorders at the clinical, biochemical and molecular levels. Over a 2-year period, we have enrolled 17 patients representing 16 Arab families. Zellweger-spectrum phenotype was observed in 12 patients and the remaining 5 had the rhizomelic chondrodysplasia punctata phenotype. We show that homozygosity mapping is a cost-effective strategy that enabled the identification of the underlying genetic defect in 100% of the cases. The pathogenic nature of the mutations identified was confirmed by immunofluorescence and complementation assays. We confirm the genetic heterogeneity of PD in our population, expand the pool of pathogenic alleles and draw some phenotype/genotype correlations.

Medium-chain acyl-CoA dehydrogenase deficiency in Saudi Arabia: incidence, genotype, and preventive implications

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD), caused by mutated ACADM gene, is a potentially fatal fatty acid oxidation defect. Detection of MCADD is now part of tandem mass spectrometry (MS-MS)-based newborn screening programs worldwide. To date, more than 67 mutations have been reported to cause MCADD with a single allele, c.985A>G, being the most common in patients of northwestern European descent. In Saudi Arabia, the Newborn Screening Program, officially launched in 2005, screens for 16 disorders including MCADD. Over a period of 3 years, 237,812 newborns were screened; 13 were identified to have MCADD giving an incidence of 1:18,293. Since the introduction of MS-MS to our institution, however, a total of 30 patients were detected to have MCADD. These cases were either newborns, at high-risk family members, or clinically suspected. The C8-carnitine levels (median 3.31, range 0.81-16.33 µM) were clearly diagnostic in all analyzed samples. Sequencing ACADM in 20 DBS revealed two novel mutations: c.362C>T (p.T121I) and c.347G>A (p.C116Y) substitutions, neither of which were detected in 300 chromosomes from controls. Eighteen (90%) patients were homozygous for the T121I mutation and two (10%) were compound heterozygous (T121I/C116Y). Our molecular data lend further support to MS-MS biochemical screening for MCADD and provide evidence for the relatively high incidence of MCADD in the Arab population. The identification of a founder mutation for MCADD has important implications for the preventive screening programs not only in Saudi Arabia but potentially also in other countries in the region.

Sphingolipid activator protein B deficiency: report of 9 Saudi patients and review of the literature

Mutated PSAP gene resulting in sphingolipid activator protein B deficiency is known to cause metachromatic leukodystrophy variant in which arylsulfatase A is normal. Of 16 patients with metachromatic leukodystrophy that were evaluated in our center, 7 patients were diagnosed with arylsulfatase A-deficient metachromatic leukodystrophy, whereas 9 children from 4 unrelated Saudi families were found to have sphingolipid activator protein B deficiency. PSAP analysis found that the 4 families segregate the same homozygous mutation that was a g.722G>C transversion resulting in C241S change, which was previously reported in an Arab patient. Our work, which reports the largest series of patients with sphingolipid activator protein B deficiency, suggests that this variant is likely to be more common than arylsulfatase A-deficient metachromatic leukodystrophy in Arabs, a notion that has potential diagnostic and preventive implications.

Variant late infantile neuronal ceroid lipofuscinosis (CLN6 gene) in Saudi Arabia

Variant late infantile neuronal ceroid lipofuscinosis is one of the multiethnically prevalent types of neuronal ceroid lipofuscinoses. Reported here are three families representing the first cases from Saudi Arabia, one of them having a novel mutation in the CLN6 gene. The CLN6-related literature is reviewed.

Allelic heterogeneity in inbred populations: the Saudi experience with Alström syndrome as an illustrative example

The increased frequency of rare autosomal recessive conditions in genetically isolated populations is a well-established phenomenon. This genetic isolation is invoked as an explanation when one particular mutation is the sole or most frequent mutation observed in a given population and is referred to as the founder effect. This trend of allelic homogeneity is contrasted by an opposite trend when the consanguinity factor is in play. Independent of endogamy at the population level, a consanguineous union is sufficient to render homozygous a percentage of the genome that is directly correlated with the degree of consanguinity. Assuming the gene in question has a normal mutation rate, the resulting homozygosity will inevitably include different defective alleles of that gene. By reporting four novel alleles, we use Alström disease to exemplify the interesting observation of allelic heterogeneity for a very rare autosomal recessive disorder in a highly inbred population. While we frequently assume founder effect in inbred populations, this report should serve to remind us of the powerful effect of the consanguinity factor, a common confounding variable among some of those populations.

Neuronal ceroid lipofuscinosis caused by MFSD8 mutations: a common theme emerging

Neuronal ceroid lipofuscinoses (NCLs) are a group of lysosomal neurodegenerative disorders that have in common the characteristic accumulation of abnormal storage material. Old clinical classification based on age of onset is now being revisited with the quickly accumulating knowledge of the various genetic defects that underlie this group of genetically heterogeneous disorders. We report our linkage data on a family with late-infantile NCL and show that the disease in this family is due to a homozygous novel mutation in the most recently described NCL gene (MFSD8). We use clinical data from our patients and the few others that have previously been reported to delineate the phenotype associated with mutations in this gene. We conclude that the phenotype is fairly consistent, which is a helpful guide to clinicians as they decide on the most cost-effective molecular testing strategies for NCLs.

Hyperornithinemia–hyperammonemia–homocitrullinuria syndrome with stroke-like imaging presentation: Clinical, biochemical and molecular analysis

Hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome is an autosomal recessive disorder caused by mutations in ORNT1 gene that encodes a mitochondrial ornithine transporter. It has variable clinical presentations with episodic hyperammonemia, liver dysfunction, and chronic neurological manifestations. In this work, we report the findings of HHH syndrome in 3 Saudi siblings. The 4-year-old proband presented with recurrent Reye-like episodes, hypotonia, and multiple stroke-like lesions on brain MRI. Biochemical and molecular analysis confirmed that she had HHH syndrome. She significantly improved on protein restriction and sodium benzoate. Her two older siblings have milder phenotypes with protein intolerance and learning problems. In comparison to their sister, their homocitrulline and orotic acid were only mildly elevated even before treatment. The three patients were homozygous for a novel mutation in ORNT1 with a Gly220Arg change. In view of the CNS lesions, which initially were felt to be suggestive of MELAS, we sequenced the entire mtDNA genome and no potential pathogenic mutations were detected. Analysis of ORNT2 did not provide explanation of the clinical and biochemical variability. This work presents a yet unreported CNS involvement pattern, notably multiple supratentorial stroke-like lesions in association with HHH syndrome. Moreover, it illustrates considerable clinical/biochemical correlation, and describes a novel mutation. We suggest including HHH syndrome in the differential diagnosis of patients found to have stroke-like lesions on brain MRI.

Muscle phosphofructokinase deficiency with neonatal seizures and nonprogressive course

Muscle phosphofructokinase deficiency is known to cause childhood-onset exercise intolerance, muscle cramps, and myoglobinuria. Rarely, phosphofructokinase deficiency manifests in infancy as congenital myopathy and arthrogryposis with fatal outcome. Here, the authors report the case of a 2-year-old boy with infantile phosphofructokinase deficiency who presented on the third day of life with intractable seizures. Two of his sisters died in infancy with hypotonia, developmental delay, and seizure disorder of unclear etiology. On follow-up, he has had hypotonia and mild developmental delay. However, he continues to gain developmental milestones, and his seizures are now well controlled on carbamazepine. This presentation suggests expanding the phenotype of muscle phosphofructokinase deficiency to include early-onset neonatal seizures. It is also unusual in the relatively milder course of the infantile form of this disorder. The authors propose that this form of glycogen storage disease be considered in the differential diagnosis of neonatal seizures and early infantile nonprogressive muscle weakness.

Craniofacial anomalies, humero-radial synostosis, rhizomelic limb shortness: Previously unrecognized autosomal recessive syndrome

Humero-radial synostosis (HRS) is a rare skeletal anomaly that might be seen in some craniosynostosis syndromes, notably Antley-Bixler syndrome, and in other disorders in association with skeletal anomalies. Here we report on two daughters of first cousin Saudi parents with syndromic HRS. Both patients had distinctive craniofacial features including cranium bifidum occultum, hypertelorism, epicanthus inversus, capillary hemangiomata, and malformed ears. Musculoskeletal examination revealed rhizomelic shortness with normal hands and feet. Skeletal survey showed bilateral HRS with no evidence of craniosynostosis. The craniofacial manifestations in these two patients do not match any of the syndromes known to be associated with HRS. We consider that the constellation is unique and apparently represents a previously unrecognized syndrome.

Determination of homocitrulline in urine of patients with HHH syndrome by liquid chromatography tandem mass spectrometry

A liquid chromatography tandem mass spectrometric method is described for the analysis of homocitrulline in human urine, a key metabolite in the differential diagnosis of hyperammonemia, hyperornithinemia, homocitrullinuria (HHH) syndrome. Urine samples were prepared by mere five-fold dilution with a mixture of internal standards (2H2-citrulline and 2H3-creatinine) used for the simultaneous quantification of creatinine. Analytes were separated on a cyano column and eluted isocratically within seven min. Detection was achieved by monitoring transitions of 190 > 84 and 190 > 127 for homocitrulline, 178 > 115 for 2H2-citrulline, 114 > 44 for creatinine and 117 > 47 for 2H3-creatinine. Calibration curves were linear up to 100 micromol/L. Intraday (n = 7) and interday (n = 6) variations were less than 10%. In urine samples from three siblings confirmed to have HHH syndrome, homocitrulline levels were at 13.3 (74), 21.1 (50) and 108.2 (103) mmol/mol creatinine (micromol/L). Control values were 0-9 mmol/mol creatinine (n = 120). The current method solves specificity issues in homocitrulline determination often encountered with some ninhydrin-based systems (coelution with methionine) and some o-phthalaldehyde-based ones (coelution with taurine), and presents an attractive alternative with a relatively high throughput.

The relationship of plasma glutamine to ammonium and of glycine to acid-base balance in propionic acidaemia

Hyperammonaemia is a common and serious complication of propionic acidaemia. Treatment of hyperammonaemia with sodium phenylacetate or phenylbutyrate has not been well studied in this disorder. We reviewed the medical records of 5 patients with propionic acidaemia over a 16-year period. We collected information on events where plasma amino acids and ammonium, plasma acids and acid-base balance, or all 3 parameters were obtained simultaneously. All patients were on protein-restricted diet and carnitine throughout the period. In contrast to hyperammonaemia in patients with a urea cycle disorder, plasma glutamine levels were below the normal mean and there was no correlation between plasma ammonium and glutamine levels. The absence of positive correlation between plasma glutamine and ammonium suggests that the routine use of sodium phenylacetate or phenylbutyrate to treat hyperammonaemia in propionic acidaemia should be questioned until further studies are done. Throughout follow-up of our propionic acidaemia patients, we have observed that plasma glycine levels correlated positively with serum bicarbonate. The association of high plasma glycine with good acid-base balance might have a potential role in management and warrants further investigation.