Journal of Medical Genetics

doi: 10.1136/jmg.2009.070573pmid: 19833603

Background The introduction of molecular karyotyping technologies facilitated the identification of specific genetic disorders associated with imbalances of certain genomic regions. A detailed phenotypic delineation of interstitial 16p13.3 duplications is hampered by the scarcity of such patients.Objectives To delineate the phenotypic spectrum associated with interstitial 16p13.3 duplications, and perform a genotype-phenotype analysis.Results The present report describes the genotypic and phenotypic delineation of nine submicroscopic interstitial 16p13.3 duplications. The critically duplicated region encompasses a single gene, CREBBP, which is mutated or deleted in Rubinstein–Taybi syndrome. In 10 out of the 12 hitherto described probands, the duplication arose de novo.Conclusions Interstitial 16p13.3 duplications have a recognizable phenotype, characterized by normal to moderately retarded mental development, normal growth, mild arthrogryposis, frequently small and proximally implanted thumbs and characteristic facial features. Occasionally, developmental defects of the heart, genitalia, palate or the eyes are observed. The frequent de novo occurrence of 16p13.3 duplications demonstrates the reduced reproductive fitness associated with this genotype. Inheritance of the duplication from a clinically normal parent in two cases indicates that the associated phenotype is incompletely penetrant.

doi: 10.1136/jmg.2009.071688pmid: 19846429

ObjectivesTo develop a comprehensive mutation analysis system with a high rate of detection, to develop a tool to predict the chance of detecting a mutation in the L1CAM gene, and to look for genotype–phenotype correlations in the X-linked recessive disorder, L1 syndrome.MethodsDNA from 367 referred patients was analysed for mutations in the coding sequences of the gene. A subgroup of 100 patients was also investigated for mutations in regulatory sequences and for large duplications. Clinical data for 106 patients were collected and used for statistical analysis.Results68 different mutations were detected in 73 patients. In patients with three or more clinical characteristics of L1 syndrome, the mutation detection rate was 66% compared with 16% in patients with fewer characteristics. The detection rate was 51% in families with more than one affected relative, and 18% in families with one affected male. A combination of these two factors resulted in an 85% detection rate (OR 10.4, 95% CI 3.6 to 30.1).The type of mutation affects the severity of L1 syndrome. Children with a truncating mutation were more likely to die before the age of 3 than those with a missense mutation (52% vs 8%; p=0.02).ConclusionsWe developed a comprehensive mutation detection system with a detection rate of almost 20% in unselected patients and up to 85% in a selected group. Using the patients' clinical characteristics and family history, clinicians can accurately predict the chance of finding a mutation. A genotype-phenotype correlation was confirmed. The occurrence of (maternal) germline mosaicism was proven.

doi: 10.1136/jmg.2009.071027pmid: 19861302

BackgroundMutations in the FUS gene have recently been discovered to be a major cause of familial amyotrophic lateral sclerosis (FALS).ObjectiveTo determine the identity and frequency of FUS gene mutations in a large cohort of Italian patients enriched in sporadic cases (SALS).MethodsExons 5, 6, 14 and 15 of the FUS gene were screened for mutations in 1009 patients (45 FALS and 964 SALS). The genetic analysis was extended to the entire coding sequence of FUS in all the FALS and 293 of the SALS patients.ResultsSeven missense mutations (p.G191S, p.R216C, p.G225V, p.G230C, p.R234C, p.G507D and p.R521C) were identified in nine patients (seven SALS and two FALS), and none in 500 healthy Italian controls. All mutations are novel except for the p.R521C mutation identified in one SALS and one FALS case. Both patients showed a similar unusual presentation, with proximal, mostly symmetrical, upper limb weakness, with neck and axial involvement. With the exception of p.G507D and p.R521C, the mutations identified in SALS patients are all localised in the glycine-rich region encoded by exon 6. In addition, eight different in-frame deletions in two polyglycine motifs were detected, the frequency of which was not significantly different in patients and controls.ConclusionsThe results show that FUS missense mutations are present in 0.7% of Italian SALS cases, and confirm the previous mutational frequency reported in FALS (4.4%). An unusual proximal and axial clinical presentation seems to be associated with the presence of the p.R521C mutation.

doi: 10.1136/jmg.2009.069369pmid: 19755429

BackgroundRecurrent microdeletions and microduplications of ∼555 kb at 16p11.2 confer susceptibility to autism spectrum disorder (ASD) in up to 1% of ASD patients. No physical or behavioural features have been identified that distinguish these individuals as having a distinct ASD subtype, but clinical data are limited.MethodsWe report five autistic probands identified by microarray analysis with copy number variation (CNV) of 16p11.2 (three deletions, two duplications). Each patient was assessed for ASD and dysmorphic features. We also describe a deletion positive 26-month-old female who has developmental delay (DD) and autistic features.ResultsProband 1 (female with ASD, de novo deletion) is not dysmorphic. Proband 2 (male with autism, de novo deletion) and proband 3 and his brother (males with autism, inherited deletions) are dysmorphic, but the two probands do not resemble one another. The mother of proband 3 has mild mental retardation (MR), minor dysmorphism and meets the criteria for ASD. Proband 4 (dysmorphic autistic male, de novo duplication) had a congenital diaphragmatic hernia. Proband 5 (non-dysmorphic ASD female with a duplication) has two apparently healthy duplication positive relatives. Probands 1 and 2 have deletion negative siblings with ASD and Asperger syndrome, respectively. Proband 6 (a female with DD and an inherited duplication) is dysmorphic, but has oligohydramnios sequence.ConclusionsThe phenotypic spectrum associated with CNV at 16p11.2 includes ASD, MR/DD and/or possibly other primary psychiatric disorders. Compared with the microduplications, the reciprocal microdeletions are more likely to be penetrant and to be associated with non-specific major or minor dysmorphism. There are deletion positive ASD probands with a less severe phenotype than deletion negative ASD siblings underscoring the significant phenotypic heterogeneity.

doi: 10.1136/jmg.2009.068619pmid: 19833602

ObjectiveThe present study investigated whether single nucleotide polymorphisms (SNPs) in the human urate transporter 1 (hURAT1) gene are associated with primary hyperuricaemia (HUA) in Han Chinese people.MethodsA total of 538 subjects (215 cases and 323 control subjects) were recruited from Qingdao, China. SNPs in potentially functional regions of the gene were identified and genotypes determined by direct sequencing. Association analyses were conducted using Fisher's exact test and logistic regression assuming a genotype model.ResultsBy sequencing the promoter, 10 exons, and the exon-intron junctions of the hURAT1 gene, 14 SNPs were identified. Two of the SNPs identified were associated with susceptibility to HUA. The first was a rare intron 3 (11 G→A) SNP (p=0.0005), where carriers of the ‘A’ allele had a 3.4-fold (95% CI 1.67 to 6.93) increased risk of HUA. The second was a common exon 8 (T1309C) SNP (rs7932775), where carriers of one and two ‘C’ alleles had respective fold increased risks of 1.64 (95% CI 1.07 to 2.52) and 2.32 (95% CI 1.37 to 3.95). These SNPs had a joint additive effect of risk of HUA, with those individuals carrying at least one ‘A’ allele at the intron 3 SNP and two ‘C’ alleles at rs7932775 having a 5.88-fold (95% CI 1.25 to 15.57) increased risk of HUA in comparison to those with no risk alleles.ConclusionIn conjunction with other studies, our results suggest that there are multiple genetic variants within or near hURAT1 that are associated with susceptibility to HUA in Han Chinese, including a novel SNP located in intron 3.