Two novel truncating variants of the ASPM gene identified in a nonconsanguineous Chinese family associated with primary microcephaly

The neurological and non-neurological roles of the primary microcephaly-associated protein ASPM

Primary microcephaly (MCPH), is a neurological disorder characterized by small brain size that results in numerous developmental problems, including intellectual disability, motor and speech delays, and seizures. Hitherto, over 30 MCPH causing genes (MCPHs) have been identified. Among these MCPHs, MCPH5, which encodes abnormal spindle-like microcephaly-associated protein (ASPM), is the most frequently mutated gene. ASPM regulates mitotic events, cell proliferation, replication stress response, DNA repair, and tumorigenesis. Moreover, using a data mining approach, we have confirmed that high levels of expression of ASPM correlate with poor prognosis in several types of tumors. Here, we summarize the neurological and non-neurological functions of ASPM and provide insight into its implications for the diagnosis and treatment of MCPH and cancer.

Genetic Primary Microcephalies: When Centrosome Dysfunction Dictates Brain and Body Size

Primary microcephalies (PMs) are defects in brain growth that are detectable at or before birth and are responsible for neurodevelopmental disorders. Most are caused by biallelic or, more rarely, dominant mutations in one of the likely hundreds of genes encoding PM proteins, i.e., ubiquitous centrosome or microtubule-associated proteins required for the division of neural progenitor cells in the embryonic brain. Here, we provide an overview of the different types of PMs, i.e., isolated PMs with or without malformations of cortical development and PMs associated with short stature (microcephalic dwarfism) or sensorineural disorders. We present an overview of the genetic, developmental, neurological, and cognitive aspects characterizing the most representative PMs. The analysis of phenotypic similarities and differences among patients has led scientists to elucidate the roles of these PM proteins in humans. Phenotypic similarities indicate possible redundant functions of a few of these proteins, such as ASPM and WDR62, which play roles only in determining brain size and structure. However, the protein pericentrin (PCNT) is equally required for determining brain and body size. Other PM proteins perform both functions, albeit to different degrees. Finally, by comparing phenotypes, we considered the interrelationships among these proteins.

Novel and recurrent ASPM mutations of founder effect in Chinese population

PURPOSE

Mutations in ASPM are the most common causes of primary microcephaly (MCPH), which is a rare brain developmental disorder with few studies in Chinese population so far. This study aimed to identify the common pathogenic variants of ASPM and estimated the incidence of MCPH5 in Guangxi population.

METHODS

We ascertained six MCPH cases caused by ASPM mutations in Guangxi Zhuang Autonomous Region, Whole-exome sequencing (WES) was performed to uncover the causal variants. The haplotype analysis was used to estimate the age of the recurrent variation.

RESULTS

Five different pathogenic variants were identified in this batch of MCPH5 cases, including two novel variants p.Ser842fs*9 and p.Lys1340Argfs*29. An rarely reported pathogenic variant, c.1789C>T/p.Arg597* was found to be a founder mutation in local population. We evaluated all ASPM variants detected among 2674 non-microcephalic individuals and estimated the MCPH5 incidence to be 5.03/1,000,000 in Guangxi population.

CONCLUSIONS

We reported the first case series of Chinese MCPH cases with ASPM mutation and revealed a highly recurrent founder mutation in this local population. MCPH5 may be the major type of congenital microcephaly in Chinese population.