Goldberg-Shprintzen syndrome is determined by the absence, or reduced expression levels, of KIFBP

Progressive ataxia, ophthalmoparesis, and hypogonadotropic hypogonadism in a family with a novel variant in the KIFBP gene

A novel homozygous variant in KIFBP was identified in a consanguineous family with four sibs affected by Goldberg-Sphrintzen Syndrome (GOSHS). We report for the first time, early-adulthood-onset progressive ataxia, opthalmoparesis, and hypogonadotropic hypogonadism in GOSHS.

Goldberg-Shprintzen Syndrome Associated with a Novel Variant in the KIFBP Gene

Goldberg-Shprintzen syndrome (GOSHS) is characterized by microcephaly, developmental delay, dysmorphic features, Hirschsprung disease (HSCR), and brain anomalies. The kinesin family binding protein (KIFBP; MIM 60937) gene has been identified as the responsible gene of the syndrome. To date, 16 different biallelic KIFBP mutations have been identified in 34 patients with GOSHS. Even though most of these mutations are nonsense and frameshift, 3 missense mutations have also been described. Here, we report an 18-month-old patient with microcephaly, developmental delay, dysmorphic features and HSCR. Exome analysis was performed to clarify the etiology of the clinical features. A previously unreported homozygous c.1723delC (p.H575Ifs*19) variant was detected in the last exon 7 of KIFBP which led to GOSHS. According to our findings, we suggest that this mutation expands mutational databases and contributes to the understanding of the phenotypic features of the syndrome.

Size matters: Large copy number losses in Hirschsprung disease patients reveal genes involved in enteric nervous system development

Hirschsprung disease (HSCR) is a complex genetic disease characterized by absence of ganglia in the intestine. HSCR etiology can be explained by a unique combination of genetic alterations: rare coding variants, predisposing haplotypes and Copy Number Variation (CNV). Approximately 18% of patients have additional anatomical malformations or neurological symptoms (HSCR-AAM). Pinpointing the responsible culprits within a CNV is challenging as often many genes are affected. Therefore, we selected candidate genes based on gene enrichment strategies using mouse enteric nervous system transcriptomes and constraint metrics. Next, we used a zebrafish model to investigate whether loss of these genes affects enteric neuron development in vivo.

This study included three groups of patients, two groups without coding variants in disease associated genes: HSCR-AAM and HSCR patients without associated anomalies (HSCR-isolated). The third group consisted of all HSCR patients in which a confirmed pathogenic rare coding variant was identified. We compared these patient groups to unaffected controls. Predisposing haplotypes were determined, confirming that every HSCR subgroup had increased contributions of predisposing haplotypes, but their contribution was highest in isolated HSCR patients without RET coding variants. CNV profiling proved that specifically HSCR-AAM patients had larger Copy Number (CN) losses. Gene enrichment strategies using mouse enteric nervous system transcriptomes and constraint metrics were used to determine plausible candidate genes located within CN losses. Validation in zebrafish using CRISPR/Cas9 targeting confirmed the contribution of UFD1L, TBX2, SLC8A1, and MAPK8 to ENS development. In addition, we revealed epistasis between reduced Ret and Gnl1 expression and between reduced Ret and Tubb5 expression in vivo. Rare large CN losses—often de novo—contribute to HSCR in HSCR-AAM patients. We proved the involvement of six genes in enteric nervous system development and Hirschsprung disease.

Hirschsprung disease is a congenital disorder characterized by the absence of intestinal neurons in the distal part of the intestine. It is a complex genetic disorder in which multiple variations in our genome combined, result in disease. One of these variations are Copy Number Variations (CNVs): large segments of our genome that are duplicated or deleted. Patients often have Hirschsprung disease without other symptoms. However, a proportion of patients has additional associated anatomical malformations and neurological symptoms. We found that CNVs, present in patients with associated anomalies, are more often larger compared to unaffected controls or Hirschsprung patients without other symptoms. Furthermore, Copy Number (CN) losses are enriched for constrained coding regions (CCR; genes usually not impacted by genomic alterations in unaffected controls) of which the expression is higher in the developing intestinal neurons compared to the intestine. We modelled loss of these candidate genes in zebrafish by disrupting the zebrafish orthologues by genome editing. For several genes this resulted in changes in intestinal neuron development, reminiscent of HSCR observed in patients. The results presented here highlight the importance of Copy Number profiling, zebrafish validation and evaluating all CCR expressed in developing intestinal neurons during diagnostic evaluation.

The mechanism of kinesin inhibition by kinesin-binding protein

Subcellular compartmentalisation is necessary for eukaryotic cell function. Spatial and temporal regulation of kinesin activity is essential for building these local environments via control of intracellular cargo distribution. Kinesin-binding protein (KBP) interacts with a subset of kinesins via their motor domains, inhibits their microtubule (MT) attachment, and blocks their cellular function. However, its mechanisms of inhibition and selectivity have been unclear. Here we use cryo-electron microscopy to reveal the structure of KBP and of a KBP-kinesin motor domain complex. KBP is a tetratricopeptide repeat-containing, right-handed α-solenoid that sequesters the kinesin motor domain's tubulin-binding surface, structurally distorting the motor domain and sterically blocking its MT attachment. KBP uses its α-solenoid concave face and edge loops to bind the kinesin motor domain, and selected structure-guided mutations disrupt KBP inhibition of kinesin transport in cells. The KBP-interacting motor domain surface contains motifs exclusively conserved in KBP-interacting kinesins, suggesting a basis for kinesin selectivity.

Goldberg-Shprintzen syndrome is determined by the absence, or reduced expression levels, of KIFBP

Goldberg-Shprintzen syndrome (GOSHS) is caused by loss of function variants in the kinesin binding protein gene (KIFBP). However, the phenotypic range of this syndrome is wide, indicating that other factors may play a role. To date, 37 patients with GOSHS have been reported. Here, we document nine new patients with variants in KIFBP: seven with nonsense variants and two with missense variants. To our knowledge, this is the first time that missense variants have been reported in GOSHS. We functionally investigated the effect of the variants identified, in an attempt to find a genotype-phenotype correlation. We also determined whether common Hirschsprung disease (HSCR)-associated single nucleotide polymorphisms (SNPs), could explain the presence of HSCR in GOSHS. Our results showed that the missense variants led to reduced expression of KIFBP, while the truncating variants resulted in lack of protein. However, no correlation was found between the severity of GOSHS and the location of the variants. We were also unable to find a correlation between common HSCR-associated SNPs, and HSCR development in GOSHS. In conclusion, we show that reduced, as well as lack of KIFBP expression can lead to GOSHS, and our results suggest that a threshold expression of KIFBP may modulate phenotypic variability of the disease.