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In Vivo Functional Study of Disease-associated Rare Human Variants Using Drosophila

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Human phenotype caused by biallelic KDM4B frameshift variant.

Sanami Takada¹, Sebastián Silva^2,3, Ivonne Zamorano⁴

¹Department of Human Genetics, Research Institute, National Center for Global Health and Medicine, Tokyo, Japan.

Clinical Genetics

|August 1, 2023

Summary

Homozygous KDM4B variants, previously thought lethal, can be viable in female humans, presenting with developmental delays. This finding expands understanding of KDM4B-related intellectual disability.

Keywords:

KDM4B autosomal dominant intellectual developmental disorder 65 autosomal recessive inheritance exome sequencing

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Area of Science:

Genetics
Developmental Biology
Human Disease

Background:

KDM4B (Lysine Demethylase 4B) encodes a histone demethylase regulating gene expression.
Loss-of-function variants in KDM4B cause autosomal dominant intellectual developmental disorder 65.
Previously, only heterozygous KDM4B variants were reported, with no cases of biallelic variants.

Purpose of the Study:

To report the first case of a patient with biallelic KDM4B pathogenic variants.
To investigate the phenotypic consequences of homozygous KDM4B variants in humans.
To compare the phenotype of a homozygous patient with her heterozygous mother.

Main Methods:

Clinical evaluation of a female patient and her heterozygous mother.
Genetic analysis to identify KDM4B variants.
Review of existing literature on KDM4B variants and associated disorders.

Main Results:

A female patient presented with a biallelic KDM4B frameshift variant (c.1384_1394delinsGGG, p.(Leu462Glyfs*43)).
The patient exhibited developmental and language delays, hypotonia, and a characteristic facial appearance.
The patient's phenotype was more severe than her heterozygous mother's, suggesting viability of homozygous variants in females.

Conclusions:

Homozygous KDM4B frameshift variants can be viable in humans, particularly in females.
This case expands the known spectrum of KDM4B-related disorders and challenges previous assumptions about embryonic lethality in homozygous states.
Further research is needed to understand the full implications of biallelic KDM4B variants.