Hallermann-Streiff syndrome: The molecular link of the well-known syndrome is still missing

Hallermann-Streiff syndrome is a rare congenital syndrome that is well-known but whose genetic cause has so far not been unraveled – although researchers have intensively investigated the disorder, using the latest applications of high-throughput sequencing, which have considerably facilitated the identification of disease-associated genes in recent years. Clinically, it presents as a combination of craniofacial dysmorphism, eye malformations, hair and skin anomalies, short stature, and, especially, a characteristic face that usually leads to the clinical diagnosis. Interestingly, affected children may also show signs of accelerated aging. Hallermann-Streiff syndrome thus belongs to the group of so called progeroid syndromes. In a review article published in the American Journal of Medical Genetics, researchers of the Institute of Human Genetics Göttingen summarize the current knowledge on the clinical characteristics of the syndrome and discuss the missing molecular link. Furthermore, they present innovative strategies that may be applied to identify the genetic basis of Hallermann-Streiff syndrome in the future.

Hallermann-Streiff syndrome: A missing molecular link for a highly recognizable syndrome.
Schmidt J, Wollnik B.
Am J Med Genet C Semin Med Genet. 2018 Dec;178(4):398-406. doi: 10.1002/ajmg.c.31668. Review.

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Rapid aging: Biallelic POLR3A mutations cause neonatal progeroid syndrome

An international collaboration of scientists including researchers of the Institute of Human Genetics Göttingen have determined specific mutations in POLR3A as the genetic cause of Wiedemann-Rautenstrauch syndrome. This rare disorder is associated with signs of accelerated aging; it is thus a so called progeroid syndrome. Affected children show characteristic features like growth retardation, sparse scalp hair, lipodystrophy and an unusual face already at birth. They appear to be prematurely aged.

POLR3A, the protein encoded by the gene, forms the largest subunit of the RNA polymerase III complex. This enzyme is crucially involved in the synthesis of RNA in transcription. Specifically, RNA polymerase III transcribes small RNAs including ribosomal RNA (rRNA) and transfer RNA (tRNA). In their study recently published in the Journal of Medical Genetics, the researchers discovered biallelic POLR3A mutations in eight affected families. The types of the identified mutations suggest that specific combinations of compound heterozygous variants of POLR3A must be present to cause the phenotype, including one variant that has a strong detrimental effect on protein function (splice-site or truncating mutation) and a variant exerting a milder functional effect (often an intronic variant).

Progeroid syndromes are a clinically heterogeneous family of disorders which share the feature of premature aging. Various genetic defects have so far been identified as molecular causes, affecting fundamental processes like chromatin structure, genome stability, transcription control, DNA repair, nuclear structure and epigenetic regulation. Researchers at the UMG Institute of Human Genetics are intensively investigating this group of disorders. Their work within this study has been funded by CRC 1002 (“Modulatory units in heart failure”; speaker Prof. Dr. Gerd Hasenfuß). The Institute has also established a special clinic for families with progeroid syndromes.

Specific combinations of biallelic POLR3A variants cause Wiedemann-Rautenstrauch syndrome
Paolacci S, Li Y, Agolini E, Bellacchio E, Arboleda-Bustos CE, Carrero D, Bertola D, Al-Gazali L, Alders M, Altmüller J, Arboleda G, Beleggia F, Bruselles A, Ciolfi A, Gillessen-Kaesbach G, Krieg T, Mohammed S, Müller C, Novelli A, Ortega J, Sandoval A, Velasco G, Yigit G, Arboleda H, Lopez-Otin C, Wollnik B*, Tartaglia M*, Hennekam RC* (*contributed equally).
J Med Genet. 2018 Oct 15; Epub ahead of print

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New genetic causes of Bloom syndrome identified

Mutations causing Bloom syndrome have been identified in two new genes by an international collaboration of scientists including also researchers of the Institute of Human Genetics Göttingen. Bloom syndrome is a rare congenital disorder characterized by primary microcephaly, growth retardation, skin affections and intellectual disability. Patients with Bloom syndrome are also predisposed to the development of cancer, with a mean age of onset in the third decade of life.

The researchers in Göttingen investigated a Turkish family with two cousins who manifested developmental delay, mild intellectual disability, pronounced primary microcephaly and short stature and were clinically diagnosed with a Bloom syndrome-like disorder. Exome sequencing identified in both affected individuals a homozygous 5-bp deletion in RMI1 as the underlying cause of the condition. The protein encoded by RMI1 is a member of the BRT protein complex – just like TOP3A, in which their collaboration partners in this study detected novel causative variants in 10 other patients with Bloom syndrome. The BTR complex plays an essential role in homologous recombination, an important mechanism in the repair of DNA damage. Homozygous mutations in BLM, another BTR component, have previously been described as causing Bloom syndrome.

The results of the study have been published in the American Journal of Human Genetics.

Martin C-A, Sarlós K, Logan CV, Thakur RS, Parry DA, Bizard AH, Leitch A, Cleal L, Ali NS, Al-Owain MA, Allen W, Altmüller J, Aza-Carmona M, Barakat BAY, Barraza-García J, Begtrup A, Bogliolo M, Cho MT, Cruz-Rojo J, Dhahrabi HAM, Elcioglu NH, GOSgene, Gorman GS, Jobling R, Kesterton I, Kishita Y, Kohda M, Le Quesne Stabej P, Malallah AJ, Nürnberg P, Ohtake A, Okazaki Y, Pujol R, Ramirez MJ, Revah-Politi A, Shimura M, Stevens P, Taylor RW, Turner L, Williams H, Wilson C, Yigit G, Zahavich L, Alkuraya FS, Surralles J, Iglesais A, Murayama K, Wollnik B, Dattani M, Heath KE, Hickson ID, Jackson AP. Mutations in TOP3A Cause a Bloom Syndrome-like Disorder. Am J Hum Genet. 2018;103(2):221-231. doi:10.1016/j.ajhg.2018.07.001.

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An evolutionarily conserved ribosome-rescue pathway maintains epidermal homeostasis

During translation, a number of obstacles have the potential to arrest the ribosomal movement. In yeast, several studies revealed that the evolutionarily conserved Pelota (Pelo) recognizes stalled ribosomes and dissociates ribosomal subunits. In mammals, little is known about the role of Pelo in the ribosome-rescue machinery. An international collaboration with the participation of Prof. Ibrahim Adham at the Institute of Human Genetics Göttingen has studied conditional mouse lines in which Pelo is deleted in different epidermal stem cell lineages. They found that loss of the ribosome-rescue factor Pelo in specific epidermal stem cell lineage results in hyperproliferation and altered differentiation of these cells. By contrast, deletion of Pelo in other epidermal stem cell lineages has no effect or induces a mild phenotype. Further molecular analyses demonstrated that the Pelo deletion results in global upregulation of translation, rather than affecting the expression of specific genes. These results reveal that the ribosome-rescue machinery is essential for mammalian tissue homeostasis.

The results of the study have been published in Nature.

Liakath-Ali K, Mills EW, Sequeira I, Lichtenberger BM, Pisco AO, Sipilä KH, Mishra A, Yoshikawa H, Wu CC, Ly T, Lamond AI, Adham IM, Green R, Watt FM. An evolutionarily conserved ribosome-rescue pathway maintains epidermal homeostasis. Nature. 2018 Apr;556(7701):376-380. doi: 10.1038/s41586-018-0032-3. Epub 2018 Apr 11.

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Molecular Biology of Hearing and Deafness conference 2018, May 16-19, 2018, in Göttingen

The 11th Molecular Biology of Hearing and Deafness Conference will be held from May 16th to 19th, 2018, at the Max Planck Institute of Biophysical Chemistry in Göttingen. This international conference serves the exchange of researchers about the latest developments in the field. Here, besides the identification of so-far unknown deafness genes, new methods of exome/genome analysis will be presented. Advances in the identification of gene-function relationships will be discussed as well as the role of specific genes in the molecular physiology of hearing and in age-dependent hearing loss. Speakers will also cover potential strategies for gene therapy and prepare the transfer of the results from basic research into clinical application.

More details can be found at Registration will be open until March 31st.

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