The genetic cause of neurodevelopmental disorders in 30 consanguineous families

Abstract

Objective: This study aims to clinically and genetically assess 30 unrelated consanguineous Pakistani families from various ethnic backgrounds, all exhibiting features of neurodevelopmental disorders (NDDs).

Methods: We conducted clinical, genetic, biochemical, and molecular analyses on 30 consanguineous families with NDDs enrolled from various regions of Pakistan. The likely molecular causes of primary microcephaly and NDDs were identified. Detailed clinical investigations and molecular diagnoses were performed using whole exome sequencing (WES) of the proband, followed by Sanger sequencing for validation and segregation in the available family members of the affected families.

Results: WES identified likely disease-causing homozygous variants in 30 unrelated consanguineous families. Six families presented newly described variants in known NDD-related genes: ABAT (c.1439 T > G; p.Phe480Cys) [OMIM613163], SLC12A6 (c.2865_2865insT; p.Glu955Asnfs*5) [OMIM 218000], SHANK3 (c.1305-3_1,305-2delTT; p.Gln29-_Gly305del) [OMIM 606232], BCKDK (c.356_356insC; p.Gly119Alafs*24) [OMIM 614923], DDHD2 (c.2065G > T; p.Asp689Tyr) [OMIM 615033], ERCC2 (c.1255G > A; p.Glu419Lys) [OMIM 610756]. Additionally, 12 families had previously reported disease-causing variants associated with different types of NDDs: ATRX (c.109C > T; p.Arg37*) [OMIM 309580], GPR56 [ADGRG1] (c.1423C > T; p.Arg475*) [OMIM 606854], NAGLU (c.1694G > A; p.Arg565Gln) [OMIM 252920], DOLK (c.3G > A; p.Met1Ile) [OMIM 610768], GPT2 (c.815C > T; p.Ser272Leu) [OMIM 616281], DYNC1I2 (c.607 + 1G > A; p.?) [OMIM 618492], FBXL3 (c.885delT; p.Leu295Phefs25*) [OMIM 606220], LINGO1 (c.869G > A; p.Arg290His) [OMIM 618103], and ASPM (c.3978G > A; Trp1326*, c.9557C > G; p.Ser3186*, c.6994C > T; p.Arg2332*) [OMIM 608716]. All the identified variants showed segregation compatible with autosomal recessive inheritance.

Conclusion: In the present study, we observed a high frequency of ASPM variants in the genetic analysis of 30 consanguineous families exhibiting features of NDDs, particularly those associated with autosomal recessive primary microcephaly. These findings contribute to studies on genotype-phenotype correlation, genetic counseling for families, and a deeper understanding of human brain function and development.

Keywords: 30 families; ASPM; WES; consanguineous marriages; neurodevelopmental disorders; novel variants.

Figure 1

Family pedigrees and Sanger sequencing chromatogram and mutation positions of 14 families.

Figure 2

Families pedigrees of 16 families (family 15–family 30). All the families revealed autosomal recessive inheritance.

Figure 3

WES filtration steps showing details of each step that was followed to identify variants in all the 30 families. Variants were classified according to the ACMG classification.

Figure 4

3D protein modeling for the variant identified in five proteins, including ABAT, BCKDK, DDHD2, ERCC2, and SLC12A6. Protein modeling revealed that the identified variants in these proteins resulted in substantial changes in the secondary structures that might lead to improper folding, structure, and function, causing severe NDDs in the affected individuals of the families.

Figure 5

3D protein modeling for the hotspot mutation (Trp1326*) identified in the present study in the ASPM gene.