VACTERL Association Etiology: The Impact of de novo and Rare Copy Number Variations

Copy number variations (CNVs), either DNA gains or losses, have been found at common regions throughout the human genome. Most CNVs neither have a pathogenic significance nor result in disease-related phenotypes but, instead, reflect the normal population variance. However, larger CNVs, which often arise de novo, are frequently associated with human disease. A genetic contribution has long been suspected in VACTERL (Vertebral, Anal, Cardiac, TracheoEsophageal fistula, Renal and Limb anomalies) association. The anomalies observed in this association overlap with several monogenetic conditions associated with mutations in specific genes, e.g. Townes Brocks (SALL1), Feingold syndrome (MYCN) or Fanconi anemia. So far VACTERL association has typically been considered a diagnosis of exclusion. Identifying recurrent or de novo genomic variations in individuals with VACTERL association could make it easier to distinguish VACTERL association from other syndromes and could provide insight into disease mechanisms. Sporadically, de novo CNVs associated with VACTERL are described in literature. In addition to this literature review of genomic variation in published VACTERL association patients, we describe CNVs present in 68 VACTERL association patients collected in our institution. De novo variations (>30 kb) are absent in our VACTERL association cohort. However, we identified recurrent rare CNVs which, although inherited, could point to mechanisms or biological processes contributing to this constellation of developmental defects.

Clinical and genetic spectrum of Sanfilippo type C (MPS IIIC) disease in The Netherlands

Mucopolysaccharidosis IIIC (MPS IIIC, Sanfilippo C syndrome) is a lysosomal storage disorder caused by deficiency of the lysosomal enzyme acetyl-CoA:alpha-glucosaminide N-acetyltransferase (HGSNAT). We performed a clinical study on 29 Dutch MPS IIIC patients and determined causative mutations in the recently identified HGSNAT gene. Psychomotor development was reported to be normal in all patients during the first year of life. First clinical signs were usually noted between 1 and 6 years (mean 3.5 years), and consisted of delayed psychomotor development and behavioral problems. Other symptoms included sleeping and hearing problems, recurrent infections, diarrhoea and epilepsy. Two sisters had attenuated disease and did not have symptoms until the third decade. Mean age of death was 34 years (range 25-48). Molecular analysis revealed mutations in both alleles for all patients except one. Altogether 14 different mutations were found: two splice site mutations, one frame shift mutation due to an insertion, three nonsense mutations and eight missense mutations. Two mutations, p.R344C and p.S518F, were frequent among probands of Dutch origin representing 22.0% and 29.3%, respectively, of the mutant alleles. This study demonstrates that MPS IIIC has a milder course than previously reported and that both severity and clinical course are highly variable even between sibs, complicating prediction of the clinical phenotype for individual patients. A clear phenotype-genotype correlation could not be established, except that the mutations p.G262R and p.S539C were only found in two sisters with late-onset disease and presumably convey a mild phenotype.

Prevalent mutations in the GALC gene of patients with Krabbe disease of Dutch and other European origin

Sixty-four unrelated patients with infantile Krabbe disease (globoid cell leukodystrophy, GLD) of Dutch (n = 41) or other European origin (n = 23) were screened for the presence of a large 30 kb deletion starting in intron 10 (IVS10del30 kb), a base substitution 1538T(T513M) and a polymorphism, 502T. The deletion and the T513M mutation were present in 52% and 8.5%, respectively, of the 82 GALC alleles of the Dutch patients. The 502T polymorphism, which had an allele frequency of 5.3% in a Dutch control panel, occurred in 65% of the GLD alleles. Analysis of patients and both parents in 26 of the families showed that del30 kb was invariably associated with 502T. However, 502T was also present on 40% of the GLD alleles with an as yet unidentified mutation, which is 7.5 times higher than its frequency in controls. This suggests that besides del30 kb at least one other relatively frequent mutation has arisen on the 502T GALC allele. A relatively high incidence of del30 kb was also found in 23 other European (non-Dutch) patients (allele frequency 35%), but T513M did not occur in this group. Practical examples described in this report illustrate the potential usefulness of mutation analysis in many families with Krabbe disease for heterozygote detection and prenatal diagnosis.