The neonatal progeroid syndrome (Wiedemann-Rautenstrauch) and its relationship to Pelizaeus-Merzbacher's disease

Premature aging disorders: A clinical and genetic compendium

Progeroid disorders make up a heterogeneous group of very rare hereditary diseases characterized by clinical signs that often mimic physiological aging in a premature manner. Apart from Hutchinson-Gilford progeria syndrome, one of the best-investigated progeroid disorders, a wide spectrum of other premature aging phenotypes exist, which differ significantly in their clinical presentation and molecular pathogenesis. Next-generation sequencing (NGS)-based approaches have made it feasible to determine the molecular diagnosis in the early stages of a disease. Nevertheless, a broad clinical knowledge on these disorders and their associated symptoms is still fundamental for a comprehensive patient management and for the interpretation of variants of unknown significance from NGS data sets. This review provides a detailed overview on characteristic clinical features and underlying molecular genetics of well-known as well as only recently identified premature aging disorders and also highlights novel findings towards future therapeutic options.

Specific combinations of biallelic POLR3A variants cause Wiedemann-Rautenstrauch syndrome

BACKGROUND

Wiedemann-Rautenstrauch syndrome (WRS) is a form of segmental progeria presenting neonatally, characterised by growth retardation, sparse scalp hair, generalised lipodystrophy with characteristic local fatty tissue accumulations and unusual face. We aimed to understand its molecular cause.

METHODS

We performed exome sequencing in two families, targeted sequencing in 10 other families and performed in silico modelling studies and transcript processing analyses to explore the structural and functional consequences of the identified variants.

RESULTS

Biallelic POLR3A variants were identified in eight affected individuals and monoallelic variants of the same gene in four other individuals. In the latter, lack of genetic material precluded further analyses. Multiple variants were found to affect POLR3A transcript processing and were mostly located in deep intronic regions, making clinical suspicion fundamental to detection. While biallelic POLR3A variants have been previously reported in 4H syndrome and adolescent-onset progressive spastic ataxia, recurrent haplotypes specifically occurring in individuals with WRS were detected. All WRS-associated POLR3A amino acid changes were predicted to perturb substantially POLR3A structure/function.

CONCLUSION

Biallelic mutations in POLR3A, which encodes for the largest subunit of the DNA-dependent RNA polymerase III, underlie WRS. No isolated functional sites in POLR3A explain the phenotype variability in POLR3A-related disorders. We suggest that specific combinations of compound heterozygous variants must be present to cause the WRS phenotype. Our findings expand the molecular mechanisms contributing to progeroid disorders.

The progeroid gene BubR1 regulates axon myelination and motor function

Myelination, the process by which oligodendrocytes form the myelin sheath around axons, is key to axonal signal transduction and related motor function in the central nervous system (CNS). Aging is characterized by degenerative changes in the myelin sheath, although the molecular underpinnings of normal and aberrant myelination remain incompletely understood. Here we report that axon myelination and related motor function are dependent on BubR1, a mitotic checkpoint protein that has been linked to progeroid phenotypes when expressed at low levels and healthy lifespan when overabundant. We found that oligodendrocyte progenitor cell proliferation and oligodendrocyte density is markedly reduced in mutant mice with low amounts of BubR1 (BubR1^H/H mice), causing axonal hypomyelination in both brain and spinal cord. Expression of essential myelin-related genes such as MBP and PLP1 was significantly reduced in these tissues. Consistent with defective myelination, BubR1^H/H mice exhibited various motor deficits, including impaired motor strength, coordination, and balance, irregular gait patterns and reduced locomotor activity. Collectively, these data suggest that BubR1 is a key determinant of oligodendrocyte production and function and provide a molecular entry point to understand age-related degenerative changes in axon myelination.

Natural course of neonatal progeroid syndrome

BACKGROUND

Several progeroid disorders presenting a specific "old-man" appearance since birth or childhood have been described. Here, five patients with a history of severe intrauterine and postnatal growth retardation and pseudohydrocephaloid cranium noted after birth that were suggestive of neonatal progeroid syndrome (NPS) or Wiedemann-Rautenstrauch syndrome are reported. We discuss the natural course of the syndrome.

METHODS

A series of anthropometric measurements, imaging, dual energy X-ray absorptiometry, and endocrine investigations to assess metabolic complications such as hyperinsulinemia and dyslipidemia were performed on these five patients who were followed for 1-7 years. Screening of inborn errors, karyotyping, chromosomal breakage rates and DNA mutational studies with direct sequencing of LMNA, ERCC8 and ZMPSTE24 genes were also performed.

RESULTS

Generalized lipodystrophy was noted in all patients except for regions such as the cheeks, hands and feet. All cases had failure to thrive, microcephaly, ear dysplasia, laryngomalacia, hearing impairment, gastro-esophageal reflux disease, constipation, abnormal dentition, dermatitis/acrodermatitis enteropathica, hyperpigmentation of the skin, very low insulin-like growth factor I levels with delayed bone age, relative hypolipidemia, initial camptodactyly/joint contracture, progressive kyphoscoliosis, osteoporosis with loose joints, ventriculomegaly, and generalized organic aciduria. Other findings included inguinal hernia, hypothyroidism or persistent hyperthyrotropinemia, cryptorchidism, hip dysplasia, growth hormone deficiency, cloudy cornea with congenital glaucoma, neonatal teeth, cardiac defects, basal ganglia calcification and seizure disorder. These patients with NPS did not show hyperinsulinemia or dyslipidemia. Their karyotypes were all normal, while the chromosomal breakage test showed markedly increased breakage rates in four patients. LMNA, ERCC8, or ZMPSTE24 gene mutations could not account for the disorders in these patients. Four patients died after sepsis or aspiration pneumonia at the age of 1.1, 4, 6.2 and 7.5 years.

CONCLUSION

Increased chromosomal breakage and the presence of basal ganglia calcification after early childhood suggest that DNA repair defects are involved in the pathogenesis of this disorder. This rare disorder represents a complex of symptoms with unknown cause and pathogenesis, and more than one disease may account for the clinical variability of NPS.

Follow-up study of Wiedemann-Rautenstrauch syndrome: Long-term survival and comparison with Rautenstrauch's patient “G”

BACKGROUND

Wiedemann-Rautenstrauch syndrome (WRS) characterizes a neonatal progeroid entity. In the last 30 years, 28 cases have been reported. In most cases of WRS, survival is short and long-term studies are impossible.

CASE

In the present report, we describe a patient with WRS followed for 17 years at the Instituto de Genética, Universidad Nacional de Colombia; this is an exceptional survival period for a person with WRS. The information collected through 17 years for the present patient provides new knowledge about the natural evolution of this syndrome. New clinical and laboratory characteristics are compared with those reported for Rautenstrauch's patient "G."

CONCLUSIONS

Our results confirm the variability of this syndrome, especially at the neurological level. However, many etiological and pathological aspects of this syndrome remain unknown.