Rare missense TUBGCP5 gene variant in a patient with primary microcephaly.

Primary microcephalies (MCPH) are characterized by microcephaly (HC -2 SD at birth) in the absence of visceral malformations. To date, less than 20 genes have been associated with MCHP, several of which are involved in the formation and function of the centrosome. Here, we report a novel missense variant in the TUBGCP5 gene in a patient with primary microcephaly and mild developmental delay. The TUBCGP5 gene (tubulin gamma complex associated protein 5) is a paralog of TUBGCP4 and TUBGCP6, both of which are known MCPH associated genes, and like its' paralogs, is involved in centrosome formation. Furthermore, the TUBGCP5 gene is located in the 15q11.2 BP1-BP2 microdeletion Burnside-Butler susceptibility locus that is part of the larger Prader-Willi/Angelman region. Common clinical features of the 15q11.2 BP1-BP2 microdeletion include general developmental and neurodevelopmental delay which may occasionally be accompanied by yet unexplained microcephaly. In our patient, the TUBGCP5:c.2180T > G, p.Phe727Cys missense variant was identified in compound heterozygous state with 15q11.2 BP1-BP2 microdeletion using whole exome sequencing, after the initial analyses of known MCPH genes failed to identify a conclusively causative variant. The identified variant is rare and highly conserved, as shown by population allele frequency data from ExAC and GnomAD, as well as comparisons with all other vertebrates. Based on this evidence we suggest that the identified TUBGCP5 variant in our patient may thus represent a novel cause of MCPH with mild developmental delay and may play a role in occurrence of microcephaly in 15q11.2 microdeletion carriers. Further studies are required to further clarify the causality and penetrance of TBGCP5 variants in primary microcephaly.

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