Expanding the clinical, allelic, and locus heterogeneity of retinal dystrophies.

PURPOSE: Retinal dystrophies (RD) are heterogeneous hereditary disorders of the retina that are usually progressive in nature. The aim of this study was to clinically and molecularly characterize a large cohort of RD patients. METHODS: We have developed a next-generation sequencing assay that allows known RD genes to be sequenced simultaneously. We also performed mapping studies and exome sequencing on familial and on syndromic RD patients who tested negative on the panel. RESULTS: Our panel identified the likely causal mutation in >60% of the 292 RD families tested. Mapping studies on all 162 familial RD patients who tested negative on the panel identified two novel disease loci on Chr2:25,550,180-28,794,007 and Chr16:59,225,000-72,511,000. Whole-exome sequencing revealed the likely candidate as AGBL5 and CDH16, respectively. We also performed exome sequencing on negative syndromic RD cases and identified a novel homozygous truncating mutation in GNS in a family with the novel combination of mucopolysaccharidosis and RD. Moreover, we identified a homozygous truncating mutation in DNAJC17 in a family with an apparently novel syndrome of retinitis pigmentosa and hypogammaglobulinemia. CONCLUSION: Our study expands the clinical and allelic spectrum of known RD genes, and reveals AGBL5, CDH16, and DNAJC17 as novel disease candidates.Genet Med 18 6, 554-562.

Expanding phenotypic and allelic heterogeneity of tricho-hepato-enteric syndrome.

Molecular genetics studies are of increasing importance in the diagnosis and classification of congenital diarrheal disorders. We describe the molecular genetic basis of tricho-hepato-enteric syndrome in patients from Saudi Arabia with novel mutations of SKIV2L (c.3559_3579del, p.1187_1193del) and TTC37 (C4102T, p.Q1368X). Interestingly, the congenital presence of café-au-lait spots and their distribution in the pelvis and lower limbs were a unique and consistent clinical feature of these patients and may aid differential diagnosis of congenital diarrheal disorders. This study expands allelic and phenotypic heterogeneity of syndromic diarrhea/tricho-hepato-enteric syndrome.

Association of a mutation in LACC1 with a monogenic form of systemic juvenile idiopathic arthritis.

OBJECTIVE: The pathologic basis of systemic juvenile idiopathic arthritis (JIA) is a subject of some controversy, with evidence for both autoimmune and autoinflammatory etiologies. Several monogenic autoinflammatory disorders have been described, but thus far, systemic JIA has only been attributed to a mutation of MEFV in rare cases and has been weakly associated with the HLA class II locus. This study was undertaken to identify the cause of an autosomal-recessive form of systemic JIA. METHODS: We studied 13 patients with systemic JIA from 5 consanguineous families, all from the southern region of Saudi Arabia. We used linkage analysis, homozygosity mapping, and whole-exome sequencing to identify the disease-associated gene and mutation. RESULTS: Linkage analysis localized systemic JIA to a region on chromosome 13 with a maximum logarithm of odds score of 11.33, representing the strongest linkage identified to date for this disorder. Homozygosity mapping reduced the critical interval to a 1.02-Mb region defined proximally by rs9533338 and distally by rs9595049. Whole-exome sequencing identified a homoallelic missense mutation in LACC1, which encodes the enzyme laccase (multicopper oxidoreductase) domain-containing 1. The mutation was confirmed by Sanger sequencing and segregated with disease in all 5 families based on an autosomal-recessive pattern of inheritance and complete penetrance. CONCLUSION: Our findings provide strong genetic evidence of an association of a mutation in LACC1 with systemic JIA in the families studied. Association of LACC1 with Crohn's disease and leprosy has been reported and justifies investigation of its role in autoinflammatory disorders.

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.

Clinical and pathological heterogeneity of a congenital disorder of glycosylation manifesting as a myasthenic/myopathic syndrome.

Congenital disorders of glycosylation are often associated with muscle weakness in apparent isolation or as part of a multi-systemic disorder. We report here the clinical and pathological features resulting from a homozygous mutation of ALG2 in an extended family. Phenotypic heterogeneity is observed among the small cohort of patients reported to date and is highlighted by our study. Linkage analysis, homozygozity mapping and whole exome sequencing followed clinical and pathological characterization of patients who presented with a congenital limb girdle pattern of weakness with no ocular or bulbar involvement. Nerve stimulation studies were consistent with a congenital myasthenic syndrome. Severity and progression of disease was variable. Muscle biopsies showed myopathic features, ragged red fibers and a sub-sarcolemmal accumulation of structurally normal mitochondria. Whole exome sequencing revealed an indel mutation c.214_224delGGGGACTGGCTdelinsAGTCCCCG, p.72_75delGDWLinsSPR in exon 1 of ALG2. Mutation of ALG2 manifested as a limb girdle pattern of muscle weakness with defects at both the neuromuscular junction and sarcomere. In addition the accumulation and distribution of mitochondria in the diseased muscle and the presence of ragged red fibers were supportive of a mitochondrial myopathy. ALG2 mutation results in a heterogeneous phenotype and care should be taken in categorization and treatment of these patients.