De novo variants in the PABP domain of PABPC1 lead to developmental delay

De Novo Splice-Site Variant in DKC1 in a Female With Clinical Features of Hoyeraal-Hreidarsson Syndrome

The dyskerin encoding gene DKC1 plays an important role in telomerase activity and telomere maintenance. Pathogenic variants in DKC1 cause an X-linked multiorgan disease called dyskeratosis congenita (DC), the most severe form of which is Hoyeraal-Hreidarsson syndrome (HHS). HHS due to DKC1 variants has so far only been reported in hemizygous males and is associated with severe neurological impairment and progressive bone marrow failure, often causing lethality in early childhood. Heterozygous carrier females are often phenotypically normal. Here, we report a young adult female carrying a de novo splice-site variant in DKC1 and presenting with clinical features overlapping with HHS, such as intrauterine and postnatal growth retardation, microcephaly, intellectual disability, and recurrent infections, while lacking other typical aspects such as dermatological manifestations, cerebellar hypoplasia, or bone marrow failure. Aberrant splicing was confirmed with an in vitro assay, and further analysis revealed very short telomere lengths in the individual, supporting a causative role of the DKC1 variant. Our observations therefore suggest that heterozygous splice-site variants in DKC1 leading to loss of function might result in a phenotype overlapping with but not being typical for HHS in females, supporting a potential genotype-phenotype correlation.

RNA binding proteins in cardiovascular development and disease

Congenital heart disease (CHD) is the most common birth defect affecting>1.35 million newborn babies worldwide. CHD can lead to prenatal, neonatal, postnatal lethality or life-long cardiac complications. RNA binding protein (RBP) mutations or variants are emerging as contributors to CHDs. RBPs are wizards of gene regulation and are major contributors to mRNA and protein landscape. However, not much is known about RBPs in the developing heart and their contributions to CHD. In this chapter, we will discuss our current knowledge about specific RBPs implicated in CHDs. We are in an exciting era to study RBPs using the currently available and highly successful RNA-based therapies and methodologies. Understanding how RBPs shape the developing heart will unveil their contributions to CHD. Identifying their target RNAs in the embryonic heart will ultimately lead to RNA-based treatments for congenital heart disease.

Loss-of-Function Variants in DRD1 in Infantile Parkinsonism-Dystonia

The human dopaminergic system is vital for a broad range of neurological processes, including the control of voluntary movement. Here we report a proband presenting with clinical features of dopamine deficiency: severe infantile parkinsonism-dystonia, characterised by frequent oculogyric crises, dysautonomia and global neurodevelopmental impairment. CSF neurotransmitter analysis was unexpectedly normal. Triome whole-genome sequencing revealed a homozygous variant (c.110C>A, (p.T37K)) in DRD1, encoding the most abundant dopamine receptor (D1) in the central nervous system, most highly expressed in the striatum. This variant was absent from gnomAD, with a CADD score of 27.5. Using an in vitro heterologous expression system, we determined that DRD1-T37K results in loss of protein function. Structure-function modelling studies predicted reduced substrate binding, which was confirmed in vitro. Exposure of mutant protein to the selective D1 agonist Chloro APB resulted in significantly reduced cyclic AMP levels. Numerous D1 agonists failed to rescue the cellular defect, reflected clinically in the patient, who had no benefit from dopaminergic therapy. Our study identifies DRD1 as a new disease-associated gene, suggesting a crucial role for the D1 receptor in motor control.