Alström Syndrome: Mutation Spectrum of ALMS1

Alström Syndrome (ALMS), a recessive, monogenic ciliopathy caused by mutations in ALMS1, is typically characterized by multisystem involvement including early cone‐rod retinal dystrophy and blindness, hearing loss, childhood obesity, type 2 diabetes mellitus, cardiomyopathy, fibrosis, and multiple organ failure. The precise function of ALMS1 remains elusive, but roles in endosomal and ciliary transport and cell cycle regulation have been shown. The aim of our study was to further define the spectrum of ALMS1 mutations in patients with clinical features of ALMS. Mutational analysis in a world‐wide cohort of 204 families identified 109 novel mutations, extending the number of known ALMS1 mutations to 239 and highlighting the allelic heterogeneity of this disorder. This study represents the most comprehensive mutation analysis in patients with ALMS, identifying the largest number of novel mutations in a single study worldwide. Here, we also provide an overview of all ALMS1 mutations identified to date.     

Atypical Alstrom syndrome with novel ALMS1 mutations precluded by current diagnostic criteria

We report on clinical and genetic studies in a non-consanguineous Irish sib-pair with infantile dilated cardiomyopathy and retinopathy. A diagnosis of Alström Syndrome (AS) was considered and diagnostic testing pursued. The Alströms gene (ALMS1) is very large (23 exons) and diagnostic testing of mutational hotspots (exon 6, 8 and 10) was negative. Furthermore the siblings were tall and did not have the typical phenotype of nystagmus, photophobia, obesity or hearing loss and so the AS diagnosis was removed. We then sought to identify the causative gene in this family using whole exome sequencing. Unexpectedly, the exome analysis identified novel compound heterozygous ALMS1 mutations in exon 5 (c.777delT:p.D260fs*26) and exon 20 (c.12145_12146insC:p.S4049fs*36) that segregated with the phenotype. Although the siblings show some clinical overlap with AS, their phenotype is not classical. It is plausible that their atypical presentation may be due to the location of the ALMS1 mutations outside the usual mutational hotspots. Our findings show how atypical cases of AS may be missed under the current diagnostic guidelines and support consideration of complete ALMS1 sequencing in children with two or more features, even if all of the core clinical features of AS are not present.     

Genetic evaluation of patients with Alström syndrome in the Polish population

Alström syndrome (AS) is a rare syndromic form of obesity and type 2 diabetes (T2D) in children coexisting with retinal dystrophy and disorders of many organs caused by the mutations in ALMS1 gene. Aim of this study was to identify the causative mutations in ALMS1 in a group of 12 patients of Polish origin with clinical symptoms of AS, and their 21 first‐degree relatives. Using DNA sequencing, nine different mutations including three novel were identified. These mutations were not present in 212 Polish individuals with no symptoms of AS, subjected to whole‐exome sequencing and collected in a national registry. Looking for genotype–phenotype relationships, we confirmed a severe phenotype in a boy with homozygous mutation in exon 16, and a relationship between a presence of T2D and mutations in exon 19. Evaluation of the type of mutation and its clinical effects gives hope for earlier diagnosis of AS in future patients and more advanced therapeutic approaches for patients with already diagnosed AS.     

Phenotypic and mutational spectrum of 21 Chinese patients with Alström syndrome

Alström syndrome (AS) is a monogenic syndromic ciliopathy caused by mutations in the ALMS1 (Alström Syndrome 1) gene. A total of 21 subjects with AS from 20 unrelated Chinese families were recruited. Our cohort consists of 9 females and 12 males, between 5 months and 20 years old. The first symptom(s) appeared between 3 and 24 months. They were recorded to be either visual impairments (83%) or dilated cardiomyopathy (17%). Median time from symptom onset to seeking medical attention was 6 months (3–36 months) and the median time needed to reach the final molecular diagnosis is 54 months (6–240 months). System involvement at the time of the survey was as follows: visual symptoms (100%), hearing Impairment (67%), endocrine symptoms (43%), neurological symptoms (19%), hepatic symptoms (14%), and renal Involvement (14%). These findings are comparable to data reported in the literature. However, the proportion of subjects with cognitive impairment (33%) and behavioral problems (19%) were higher. Thirty‐three unique mutations were identified in the ALMS1 gene, of which 18 are novel mutations classified as pathogenic/likely pathogenic according to the American College of Medical Genetics (ACMG) guideline. Four recurrent mutations were identified in the cohort, in particular; c.2084C>A, p. (Ser695Ter), is suggestive to be a founder mutation in people of Chinese ancestry. The participation of AS subjects of differing ethnicities is essential to improve the algorithm in facial recognition/phenotyping, as well as to understand the mutation spectrum beyond than just those of European ancestry.     

A novel ALMS1 splice mutation in a non-obese juvenile-onset insulin-dependent syndromic diabetic patient

Insulin-dependent juvenile-onset diabetes may occur in the context of rare syndromic presentations suggesting monogenic inheritance rather than common multifactorial autoimmune type 1 diabetes. Here, we report the case of a Lebanese patient diagnosed with juvenile-onset insulin-dependent diabetes presenting ketoacidosis, early-onset retinopathy with optic atrophy, hearing loss, diabetes insipidus, epilepsy, and normal weight and stature, who later developed insulin resistance. Despite similarities with Wolfram syndrome, we excluded the WFS1 gene as responsible for this disease. Using combined linkage and candidate gene study, we selected ALMS1, responsible for Alström syndrome, as a candidate gene. We identified a novel splice mutation in intron 18 located 3 bp before the intron–exon junction (IVS18-3T>G), resulting in exon 19 skipping and consequent frameshift generating a truncated protein (V3958fs3964X). The clinical presentation of the patient significantly differed from typical Alström syndrome by the absence of truncal obesity and short stature, and by the presence of ketoacidotic insulin-dependent diabetes, optic atrophy and diabetes insipidus. Our observation broadens the clinical spectrum of Alström syndrome and suggests that ALMS1 mutations may be considered in patients who initially present with an acute onset of insulin-dependent diabetes.     

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.     

Homozygosity for a FBN1 missense mutation: clinical and molecular evidence for recessive Marfan syndrome

Marfan syndrome (MFS) is known as an autosomal-dominant connective tissue disorder (MIM 154,700), involving primarily the skeletal, ocular and cardiovascular systems, and caused by mutations in the gene for fibrillin1 (FBN1). Here, we report on two cousins from a consanguineous family with a homozygous c.1,453C>T FBN1 mutation (p.Arg485Cys) and MFS. All four healthy parents were heterozygous for the c.1,453C>T FBN1 mutation and none fulfilled the Ghent criteria for MFS. This family is the first molecularly confirmed recessive MFS. The demonstration of recessive cases of MFS has obvious implications for genetic counselling as well as for molecular diagnosis.     

OCRL1 mutation analysis in French Lowe syndrome patients: implications for molecular diagnosis strategy and genetic counseling

The oculocerebrorenal syndrome of Lowe (OCRL) is a rare X-linked recessively inherited disease characterized by a severe pleiotropic phenotype including mental retardation, bilateral congenital cataract, and renal Fanconi syndrome. The gene responsible for OCRL encodes an inositol polyphosphate-5-phosphatase. We performed mutation analysis in 36 families and characterized 27 new mutations with two of them being recurrent mutations. The panel of mutations consisted of 27 truncating mutations (frameshift, nonsense, splice site mutations, and large genomic deletions), one in-frame deletion, and six missense mutations. The four large genomic deletions occurred in the first half of the gene, whereas all the remaining mutations took place in the second part of the gene and were concentrated in a few exons. This distribution may be of interest in terms of screening strategy when looking for unknown mutations. Haplotyping of the families was performed to analyze segregation of the mutated loci, and revealed a somatic mosaicism in one family. This is the second case of mosaicism we characterized in a total panel of 44 unrelated families affected by Lowe's syndrome. Considering the low number of families investigated, it appeared that somatic and germinal mosaicisms are quite common in this disease and must be taken into account for genetic counseling.     

Monogenic diabetes syndromes: Locus‐specific databases for Alström,Wolfram, and Thiamine‐responsive megaloblastic anemia

We developed a variant database for diabetes syndrome genes, using the Leiden Open Variation Database platform, containing observed phenotypes matched to the genetic variations. We populated it with 628 published disease‐associated variants (December 2016) for: WFS1 (n = 309), CISD2 (n = 3), ALMS1 (n = 268), and SLC19A2 (n = 48) for Wolfram type 1, Wolfram type 2, Alström, and Thiamine‐responsive megaloblastic anemia syndromes, respectively; and included 23 previously unpublished novel germline variants in WFS1 and 17 variants in ALMS1. We then investigated genotype–phenotype relations for the WFS1 gene. The presence of biallelic loss‐of‐function variants predicted Wolfram syndrome defined by insulin‐dependent diabetes and optic atrophy, with a sensitivity of 79% (95% CI 75%–83%) and specificity of 92% (83%–97%). The presence of minor loss‐of‐function variants in WFS1 predicted isolated diabetes, isolated deafness, or isolated congenital cataracts without development of the full syndrome (sensitivity 100% [93%–100%]; specificity 78% [73%–82%]). The ability to provide a prognostic prediction based on genotype will lead to improvements in patient care and counseling. The development of the database as a repository for monogenic diabetes gene variants will allow prognostic predictions for other diabetes syndromes as next‐generation sequencing expands the repertoire of genotypes and phenotypes. The database is publicly available online at https://lovd.euro-wabb.org .     

Orbital pseudotumor in a child: diagnostic implications and treatment strategies

Orbital pseudotumor is a benign, idiopathic, non-infectious and non-neoplastic clinical syndrome characterized by the presence of an inflammatory mass at orbital level with no identifiable cause. The disease is rarely observed in the pediatric population. This article describes a relapsing bilateral orbital pseudotumor in a young girl. The diagnostic implications and treatment strategies are discussed.     

Otopalatodigital syndrome type 2 in two siblings with a novel filamin A 629G>T mutation: clinical, pathological, and molecular findings

Otopalatodigital syndrome type 2 (OPD2) is an uncommon X-linked condition characterized by dysmorphic facies, a skeletal dysplasia affecting the axial and appendicular skeleton and extraskeletal anomalies including malformations of the brain, heart, genitourinary system, and intestines. Missense mutations of the FLNA gene, which encodes for the protein filamin A, have recently been shown to cause OPD2 and the allelic syndromes otopalatodigital type 1, Melnick-Needles, and frontometaphyseal dysplasia. Collectively these conditions constitute the otopalatodigital spectrum disorders. We report on two sibs affected by OPD2. The diagnosis was achieved at autopsy of a macerated male stillborn with typical external and skeletal findings of OPD2. A subsequent pregnancy was terminated due to ultrasonographic findings resembling those observed in the previous sibling. Histopathological studies revealed osseus sclerosis and do not support the previously reported membranous ossification defect observed in this condition. Mutation analysis demonstrated a novel mutation, 629G>T, in FLNA that had arisen de novo in the mother. This missense mutation predicts the substitution C210F within the second calponin homology domain of the actin-binding domain of filamin A. The identical substitution has been recently identified in an analogous amino-acid position within the actin binding domain of beta-spectrin leading to hereditary spherocytosis. The observation that phenylalanine is normally present in the same position in other proteins (utrophin, dystrophin) but leads to disease when present in filamin A implies that the function and/or structure of these actin binding domains are not entirely equivalent.     

Development and clinical implications of a novel CRISPR-based diagnostic test for pulmonary Aspergillus fumigatus infection

BackgroundRapid and reliable diagnostic methods for Aspergillus fumigatus infection are urgently needed. Clustered regularly interspaced short palindromic repeat (CRISPR)-associated protein 13a (Cas13a) has high sensitivity and specificity in the diagnosis of viral infection. However, its potential use in detecting A. fumigatus remains unexplored. A highly sensitive and specific method using the CRISPR/Cas13a system was developed for the reliable and rapid detection of A. fumigatus.MethodsThe conserved internal transcribed spacer (ITS) region of A. fumigatus was used to design CRISPR-derived RNA (crRNA) and the corresponding recombinase polymerase amplification (RPA) primer sequence with the T7 promoter for the CRISPR assay. Twenty-five clinical isolates and 43 bronchoalveolar lavage fluid (BALF) remaining from routine examinations of patients with confirmed pulmonary aspergillosis were collected to further validate the CRISPR assay.ResultsNo amplification signal was observed when genomic DNA from closely clinically related Aspergillus species, such as Aspergillus flavus, Aspergillus niger, and Aspergillus terreus, as well as Monascus purpureus Went and Escherichia coli, was tested by this assay, and the detection limit for A. fumigatus was 3 copies in a single reaction system. Validation experiments using the 25 clinical isolates demonstrated 91.7% specificity for the A. fumigatus section, and the sensitivity was 100% when first-generation sequencing was used as the standard. There was no significant difference between the PCR and CRISPR methods (P = 1.0), and the diagnosis results of the two methods were consistent (Kappa = 0.459, P = 0.003).ConclusionThe study offers a new validated CRISPR/Cas13a technique for A. fumigatus detection, providing a simple, rapid and affordable test that is ready for application in the diagnosis of A. fumigatus infection.