Study of the Pathophysiology of RNU4ATAC and RTTN Associated Syndromes

Condition(s) studied

Investigational drug(s) / intervention(s)

Blood samples: Blood samples of 5 ml to 15 ml depending on their weight

Skin biopsies: Biopsies of fragment of skin 2 to 3 mm long by 1 mm wide and 1 mm deep will preferably be taken on the inside of the arm, in the upper third, between the bend of the elbow and the hollow of the armpit under strict sterility conditions.

Fetal samples: Skin, muscle, brain and bone biopsies will be collected from fetuses in the autopsy room after the medical termination of pregnancy or miscarriage

Study summary

In the human genome, about 750 genes contain one intron excised by the minor spliceosome. These genes are named U12 genes, and these introns, minor or U12 introns. The minor spliceosome comprises its own set of snRNAs, among which U4atac. Its non-coding gene, RNU4ATAC, has been found mutated in Taybi-Linder (TALS), Roifman (RFMN) and Lowry-Wood syndromes (LWS). These rare developmental disorders associate ante- and post-natal growth retardation, microcephaly, skeletal dysplasia, intellectual disability, retinal dystrophy and immunodeficiency. Their physiopathological mechanisms remain unsolved: the number of U12 genes involved, their identity and function, or the cellular mechanisms impacted by the splicing defect, are still unknown.

The hypothesis of the study is that U12 genes coding for primary cilia components are particularly sensitive to minor splicing defects caused by RNU4ATAC mutations. Indeed, a child showing signs of TALS but negative for RNU4ATAC was found to carry a homozygous variant in the RTTN gene, coding for the rotatin protein located at the centrosome and the base of the primary cilia and playing a role in maintaining these structures. In addition, bi-allelic RNU4ATAC mutations were identified in five patients presenting with traits suggestive of the Joubert syndrome (JBTS), a well-characterized ciliopathy. These patients also present with traits typical of TALS/RFMN/LWS.

To better understand the causes of these pathologies, a cohort of patients with syndromes associated with bi-allele mutations of the RNU4ATAC or RTTN gene will be gathered, in order to conduct studies on the cells of these patients. Blood samples will be taken, as well as skin biopsies, if possible. These samples will be used to create induced pluripotent stem cell lines. Blood samples will also be collected from the parents of RNU4ATAC patients, to eliminate in transcriptomic analyses expression variations due to differences in genetic background. Biopsies of skin, muscle and brain tissue will be collected on foetuses carrying two-allele RNU4ATAC or RTTN mutations whose parents have had a miscarriage or have chosen to have a medical abortion. The biological samples collected will be used to study the transcription level of U12 genes, the splicing of their pre-messenger RNA, their main cellular functions, and the structural characteristics of tissues and cells.

Eligibility

Primary outcome measure(s)

• Identification of RNU4ATAC mutations consequences at the cellular level — 5 years
  The dysfunctions present in the different cell types obtained from RNU4ATAC patients will be identified by comparison with the controls, and will be compared with those present in RTTN patients. Consequences in cells of patients of RNU4ATAC mutations on the length and the structure of the primary cilium, as measured by fluorescence microscopy, and on the formation of small nuclear ribonucleoprotein (snRNPs) particles, as measured by glycerol gradient sedimentation analysis

Trial sites (6)

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