Compound heterozygous loss-of-function mutations in KIF20A are associated with a novel lethal congenital cardiomyopathy in two siblings.

Congenital or neonatal cardiomyopathies are commonly associated with a poor prognosis and have multiple etiologies. In two siblings, a male and female, we identified an undescribed type of lethal congenital restrictive cardiomyopathy affecting the right ventricle. We hypothesized a novel autosomal recessive condition. To identify the cause, we performed genetic, in vitro and in vivo studies. Genome-wide SNP typing and parametric linkage analysis was done in a recessive model to identify candidate regions. Exome sequencing analysis was done in unaffected and affected siblings. In the linkage regions, we selected candidate genes that harbor two rare variants with predicted functional effects in the patients and for which the unaffected sibling is either heterozygous or homozygous reference. We identified two compound heterozygous variants in KIF20A; a maternal missense variant (c.544C>T: p.R182W) and a paternal frameshift mutation (c.1905delT: p.S635Tfs*15). Functional studies confirmed that the R182W mutation creates an ATPase defective form of KIF20A which is not able to support efficient transport of Aurora B as part of the chromosomal passenger complex. Due to this, Aurora B remains trapped on chromatin in dividing cells and fails to translocate to the spindle midzone during cytokinesis. Translational blocking of KIF20A in a zebrafish model resulted in a cardiomyopathy phenotype. We identified a novel autosomal recessive congenital restrictive cardiomyopathy, caused by a near complete loss-of-function of KIF20A. This finding further illustrates the relationship of cytokinesis and congenital cardiomyopathy.

The diagnostic value of next generation sequencing in familial nonsyndromic congenital heart defects.

To determine the diagnostic value of massive parallel sequencing of a panel of known cardiac genes in familial nonsyndromic congenital heart defects (CHD), targeted sequencing of the coding regions of 57 genes previously implicated in CHD was performed in 36 patients from 13 nonsyndromic CHD families with probable autosomal dominant inheritance. Following variant analysis and Sanger validation, we identified six potential disease causing variants in three genes (MYH6, NOTCH1, and TBX5), which may explain the defects in six families. Several problematic situations were encountered when performing genotype-phenotype correlations in the families to confirm the causality of these variants. In conclusion, by screening known CHD-associated genes in well-selected nonsyndromic CHD families and cautious variant interpretation, potential causative variants were identified in less than half of the families (6 out of 13; 46%). Variant interpretation remains a major challenge reflecting the complex genetic cause of CHD.

MEIS2 involvement in cardiac development, cleft palate, and intellectual disability.

MEIS2 has been associated with cleft palate and cardiac septal defects as well as varying degrees of intellectual disability. We present a female patient with a more severe phenotype compared to previous reported patients. She has multiple congenital malformations; cleft palate and congenital heart defect characterized by septal defects and aortic coarctation. She has severe feeding problems, facial dysmorphism, severely delayed gross motor and verbal development, and autism spectrum disorder. Facial dysmorphism consisting of bitemporal narrowing, arched and laterally extended eyebrows, mild upslanting palpebral fissures, deep-set eyes, a tented upper lip, thin upper vermilion, full lower vermilion, broad first ray of hands and feet, a gap between the first and second toes, and syndactyly of toe II-III. Exome sequencing revealed a non-frameshift deletion (c.998_1000del:p.Arg333del) of three base pairs in the MEIS2 homeodomain. The more severe phenotype is most probably due to dominant-negative mechanisms. This is the first report showing a de novo small intragenic mutation in MEIS2 and further confirms the important role of this gene in normal development.

Homozygous loss-of-function mutation in ALMS1 causes the lethal disorder mitogenic cardiomyopathy in two siblings.

BACKGROUND: Two siblings from consanguineous parents of Turkish descent presented with isolated dilated cardiomyopathy, leading to early death in infancy. The diagnosis of mitogenic cardiomyopathy was made histologically. METHODS AND RESULTS: Linkage analysis combined with exome sequencing identified a homozygous deleterious mutation in the ALMS1 gene as the cause of this phenotype. CONCLUSIONS: Alström syndrome is characterized by a typically transient dilating cardiomyopathy in infancy, suggesting that mitogenic cardiomyopathy represents the extreme phenotype, resulting in demise before the other clinical symptoms become evident. This observation further illustrates the role of ALMS1 and cell cycle regulation.

Discrimination of single nucleotide mutation by using a new class of immobilized shared-stem double-stranded DNA probes.

An improved technique for single nucleotide mismatch discrimination using immobilized double-stranded DNA probes with a shared-stem hairpin (SH) structure is developed. A hairpin-like double-stranded DNA probe without any chromophore was immobilized on an agarose film-coated slide. The base number of the stem area was increased to 9-19 nt and the entire shared-stem area was included in the hybridization area, in which a mutated nucleotide was introduced in the middle. For the perfect match SH probe, we introduced an inner mismatch in the middle positon of the complementary chain. After the introduction of the inner mismatch, the hybridization ability of the SHP probe with a long stem was enhanced significantly. On the other hand, the mismatch probe was not able to hybridize to the perfect matched target. The annealing properties, specificity and hybridization dynamics of this kind of double-stranded DNA probes immobilized on an agarose film are greatly improved in comparison with those for the linear ones and traditional hairpin-like ones. Collectively we demonstrated that this type of immobilized double-stranded DNA probes had an excellent discrimination ratio for single nucleotide mismatches.