A homozygous RAB3GAP2 mutation causes Warburg Micro syndrome.
Warburg Micro syndrome and Martsolf syndrome are clinically overlapping autosomal recessive conditions characterized by congenital cataracts, microphthalmia, postnatal microcephaly, and developmental delay. The neurodevelopmental and ophthalmological phenotype is more severe in Warburg Micro syndrome in which cerebral malformations and severe motor and mental retardation are common. While biallelic loss-of-function mutations in RAB3GAP1 are present in the majority of patients with Warburg Micro syndrome; a hypomorphic homozygous splicing mutation of RAB3GAP2 has been reported in a single family with Martsolf syndrome. Here, we report a novel homozygous RAB3GAP2 small in-frame deletion, c.499_507delTTCTACACT (p.Phe167_Thr169del) that causes Warburg Micro syndrome in a girl from a consanguineous Turkish family presenting with congenital cataracts, microphthalmia, absent visually evoked potentials, microcephaly, polymicrogyria, hypoplasia of the corpus callosum, and severe developmental delay. No RAB3GAP2 mutations were detected in ten additional unrelated patients with RAB3GAP1-negative Warburg Micro syndrome, consistent with further genetic heterogeneity. In conclusion, we provide evidence that RAB3GAP2 mutations are not specific to Martsolf syndrome. Rather, our findings suggest that loss-of-function mutations of RAB3GAP1 as well as functionally severe RAB3GAP2 mutations cause Warburg Micro syndrome while hypomorphic RAB3GAP2 mutations can result in the milder Martsolf phenotype. Thus, a phenotypic severity gradient may exist in the RAB3GAP-associated disease continuum (the "Warburg-Martsolf syndrome") which is presumably determined by the mutant gene and the nature of the mutation.
Institute of Human Genetics, University of Cologne, Kerpener Str. 34, 50931, Cologne, Germany. guntram.borck@uk-koeln.de
Guntram
G
Borck
Heidrun
H
Wunram
Angela
A
Steiert
Alexander E
AE
Volk
Friederike
F
Körber
Sigrid
S
Roters
Peter
P
Herkenrath
Bernd
B
Wollnik
Deborah J
DJ
Morris-Rosendahl
Christian
C
Kubisch
D000015:Abnormalities, Multiple / Q000235:genetics; D061085:Agenesis of Corpus Callosum; D001483:Base Sequence; D002386:Cataract / Q000151:congenital / Q000235:genetics; D003241:Consanguinity; D003315:Cornea / Q000002:abnormalities; D005091:Exons / Q000235:genetics; D005260:Female; D020022:Genetic Predisposition to Disease; D006720:Homozygote; D006801:Humans; D007006:Hypogonadism / Q000235:genetics; D007223:Infant; D008607:Intellectual Disability / Q000235:genetics; D008831:Microcephaly / Q000235:genetics; D008969:Molecular Sequence Data; D009896:Optic Atrophy / Q000235:genetics; D012326:RNA Splicing / Q000235:genetics; D017384:Sequence Deletion; D020692:rab3 GTP-Binding Proteins / Q000235:genetics*
C555465:RAB3GAP2 protein, human; D020692:rab3 GTP-Binding Proteins