Rare Pathogenic Variants in Genes Implicated in Glutamatergic Neurotransmission Pathway Segregate with Schizophrenia in Pakistani Families

Preliminary studies on apparent mendelian psychotic disorders in consanguineous families

BACKGROUND

Psychiatric disorders are characterized by alteration in emotions, mood and behavior. Genetics is known to play a significant role in the development of psychiatric disorders. Genome-wide association studies have identified several loci associated with psychiatric illnesses. We hypothesize the existence of rare variants following Mendelian recessive mode of inheritance. These variants can be identified in families with multiple affected individuals born to unaffected consanguineous parents.

METHODS

We visited psychiatric outpatient departments of multiple hospitals in Lahore, Pakistan. We focused on psychosis, as it can occur in several DSM disorders such as schizophrenia, dementia and bipolar disorder. After clinical diagnosis by an American trained psychiatrist, detailed clinical assessments using Diagnostic Interview for Genetic Studies (DIGS), Diagnostic Interview for Psychosis and Affective Disorders (DI-PAD), Positive and Negative Syndrome Scale (PANSS), Hamilton Depression and Anxiety Rating Scale (HAM-D; HAM-A) were administered to all willing affected and unaffected participants.

RESULTS

We identified eight pedigrees with two or more psychotic individuals in each family. Clinical diagnoses determined by their psychiatrists included ten individuals with schizophrenia; four individuals with psychosis and bipolar disorder; and two patients with "unspecified psychosis." The rating instruments rigorously confirmed the diagnosis of psychosis in the affected patients from the six families as well as the absence of psychotic disorders in unaffected individuals from the six families. We obtained DNA samples from willing members of all eight families for future genetic analyses.

CONCLUSION

Our research highlights an alternative approach to discovery of rare recessively inherited genetic variants causing psychiatric disorders that have remained unidentified to date. These findings could illuminate underlying biological mechanisms leading toward development of targeted therapies in future.

RGS3 and IL1RAPL1 missense variants implicate defective neurotransmission in early-onset inherited schizophrenias

BACKGROUND

Schizophrenia is characterized by hallucinations, delusions and disorganized behaviour. Recessive or X-linked transmissions are rarely described for common psychiatric disorders. We examined the genetics of psychosis to identify rare large-effect variants in patients with extreme schizophrenia.

METHODS

We recruited 2 consanguineous families, each with patients affected by early-onset, severe, treatment-resistant schizophrenia. We performed exome sequencing for all participants. We checked variant rarity in public databases and with ethnically matched controls. We performed in silico analyses to assess the effects of the variants on proteins.

RESULTS

Structured clinical evaluations supported diagnoses of schizophrenia in all patients and phenotypic absence in the unaffected individuals. Data analyses identified multiple variants. Only 1 variant per family was predicted as pathogenic by prediction tools. A homozygous c.649C > T:p.(Arg217Cys) variant in RGS3 and a hemizygous c.700A > G:p.(Thr234Ala) variant in IL1RAPL1 affected evolutionary conserved amino acid residues and were the most likely causes of phenotype in the patients of each family. Variants were ultra-rare in publicly available databases and absent from the DNA of 400 ethnically matched controls. RGS3 is implicated in modulating sensory behaviour in Caenorhabditis elegans. Variants of IL1RAPL1 are known to cause nonsyndromic X-linked intellectual disability with or without human behavioural dysfunction.

LIMITATIONS

Each variant is unique to a particular family's patients, and findings may not be replicated.

CONCLUSION

Our work suggests that some rare variants may be involved in causing inherited psychosis or schizophrenia. Variant-specific functional studies will elucidate the pathophysiology relevant to schizophrenias and motivate translation to personalized therapeutics.