Identification of mutation in ASPM gene in microcephaly families from Khyber Pakhtunkhwa.

BACKGROUND

Microcephaly is a neurodevelopmental disorder characterized by a reduced head circumference, non-progressive intellectual disability (ID), and a smaller brain size relative to the age and sex-matched population. The condition is heterogeneous, with both environmental and genetic causes. Among the 27 genes implicated in its pathogenesis, the ASPM gene, primarily an autosomal recessive disorder, accounts for over 40% of reported cases, making it a key contributor to the genetic basis of microcephaly.

METHOD AND MATERIAL: In this study, two families (A and B) of Pashtun ethnicity from the Khyber Pakhtunkhwa (KPK) province of Pakistan were recruited. The phenotype in both families suggested the involvement of the ASPM gene, leading to its analysis via Sanger sequencing in affected members. For Family A, RNA was isolated from whole blood samples to assess the impact of the identified mutation on the ASPM transcript.

RESULTS

In Family A, Sanger sequencing revealed a nonsense mutation in the ASPM gene, c.9557 C > G (p.S3186*), along with an additional polymorphism (rs199422189) in affected members. This mutation, previously reported in MCPH cases from the KPK province, is known to cause nonsense-mediated decay (NMD) of the mRNA. The analysis indicated that ASPM transcripts could evade NMD in blood cells, though the presence of ASPM transcripts in the brain could not be confirmed. In Family B, a novel homozygous DNA variant, c.9316_9316delA, was identified in exon 22 of the ASPM gene, leading to a premature stop codon. However, this genetic variation did not co-segregate with the MCPH phenotype in carrier family members, indicating it might be non-pathogenic or not the primary cause of microcephaly in this family.

CONCLUSION

The study identified a known pathogenic mutation in the ASPM gene in Family A, confirming its role in microcephaly. In contrast, the novel genetic variation found in Family B did not appear to be the primary cause of the condition. Further investigations, including real-time PCR, are necessary to explore differences in ASPM transcript expression and to confirm the presence of these transcripts in relevant tissues such as the brain.