Two brothers with Martsolf's syndrome

Hypogonadotropic hypogonadism due to variants in RAB3GAP2: expanding the phenotypic and genotypic spectrum of Martsolf syndrome

Biallelic pathogenic variants in RAB3GAP2 cause Warburg Micro syndrome (WARBM) and Martsolf syndrome (MS), two rare, phenotypically overlapping disorders characterized by congenital cataracts, intellectual disability, and hypogonadism. Although the initial report documented hypergonadotropic hypogonadism (implying a gonadal defect), an adolescent girl with WARBM/MS was subsequently reported to have hypogonadotropic hypogonadism (implying a central defect in either the hypothalamus or anterior pituitary). However, in adult MS, hypogonadotropism has not been convincingly demonstrated. Additionally, the correlation between the pathogenic severity of variants in RAB3GAP2 and the phenotypic severity also remains unclear. Here we present a clinical report of a woman with congenital cataracts, apparent intellectual disability, and pubertal failure who underwent exome sequencing (ES) to determine a precise molecular diagnosis. Reproductive phenotypes reported previously in individuals with MS and the genotypic spectrum of previous RAB3GAP2 variants were also reviewed. The ES identified pathogenic compound heterozygous RAB3GAP2 variants (c.387-2A > G; p.(Arg428Glu)) combined with her phenotypic features, which enabled a unifying molecular diagnosis of MS. Reproductive evaluation confirmed a normosmic idiopathic hypogonadotropic hypogonadism. Review of the RAB3GAP2 allelic spectrum in WARBM/MS suggests that although variants resulting in complete abrogation of RAB3GAP2 protein function cause severe WARBM, variants associated with partially preserved RAB3GAP2 function cause milder MS. This report expands the genotypic and phenotypic spectrum of MS and demonstrates hypogonadotropic hypogonadism as a key pathophysiologic abnormality in MS. Genotype-phenotype associations of previously reported RAB3GAP2 variants indicate that variants that fully abolish RAB3GAP2 function result in WARBM, whereas MS is associated with variants of lesser severity with residual RAB3GAP2 function.

Mutation spectrum in RAB3GAP1, RAB3GAP2, and RAB18 and genotype-phenotype correlations in warburg micro syndrome and Martsolf syndrome

Warburg Micro syndrome and Martsolf syndrome (MS) are heterogeneous autosomal-recessive developmental disorders characterized by brain, eye, and endocrine abnormalities. Causative biallelic germline mutations have been identified in RAB3GAP1, RAB3GAP2, or RAB18, each of which encode proteins involved in membrane trafficking. This report provides an up to date overview of all known disease variants identified in 29 previously published families and 52 new families. One-hundred and forty-four Micro and nine Martsolf families were investigated, identifying mutations in RAB3GAP1 in 41% of cases, mutations in RAB3GAP2 in 7% of cases, and mutations in RAB18 in 5% of cases. These are listed in Leiden Open source Variation Databases, which was created by us for all three genes. Genotype-phenotype correlations for these genes have now established that the clinical phenotypes in Micro syndrome and MS represent a phenotypic continuum related to the nature and severity of the mutations present in the disease genes, with more deleterious mutations causing Micro syndrome and milder mutations causing MS. RAB18 has not yet been linked to the RAB3 pathways, but mutations in all three genes cause an indistinguishable phenotype, making it likely that there is some overlap. There is considerable genetic heterogeneity for these disorders and further gene identification will help delineate these pathways.

RAB3GAP1, RAB3GAP2 and RAB18: disease genes in Micro and Martsolf syndromes

Micro syndrome (OMIM 60018) and Martsolf syndrome (OMIM 21270) are related rare autosomal recessive disorders characterized by ocular and neurological abnormalities and hypothalamic hypogonadism. Micro syndrome has been associated with causative mutations in three disease genes: RAB3GAP1, RAB3GAP2 and RAB18. Martsolf syndrome has been associated with a mutation in RAB3GAP2. The present review summarizes the current literature on these genes and the proteins they encode.

Martsolf syndrome in Japanese siblings

We describe a Japanese brother and sister with Martsolf syndrome. They had short stature, severe mental retardation, cataract, hypogonadism, craniofacial dysmorphism, and bone and joint symptoms including scoliosis, lax finger joints, and talipes valgus. Previously undescribed findings included proximal femoral epiphyseal dysplasia reminiscent of Legg-Calve-Perthes disease in both patients, and Klippel-Feil malformation and osteopathia striata in one patient. Brain MRI showed mild frontal and temporal lobe atrophy, and mild ventricular enlargement. Severe GH deficiency was demonstrated after insulin tolerance and glucagon/propranolol tolerance tests. No responses to serum LH and FSH after a gonadotropin-releasing hormone (GnRH) test suggested secondary hypogonadism, that is, hypogonadotropic hypogonadism, due to hypothalamus-pituitary axis insufficiency in both patients.

Mutation in Rab3 GTPase-activating protein (RAB3GAP) noncatalytic subunit in a kindred with Martsolf syndrome

We identified a homozygous missense mutation in the noncatalytic subunit (RAB3GAP2) of RAB3GAP that results in abnormal splicing in a family with congenital cataracts, hypogonadism, and mild mental retardation (Martsolf syndrome). Recently, mutations in the catalytic subunit of RAB3GAP (RAB3GAP1), a key regulator of calcium-mediated hormone and neurotransmitter exocytosis, were reported in Warburg micro syndrome, a severe neurodevelopmental condition with overlapping clinical features. RAB3GAP is a heterodimeric protein that consists of a catalytic subunit and a noncatalytic subunit encoded by RAB3GAP1 and RAB3GAP2, respectively. We performed messenger RNA-expression studies of RAB3GAP1 and RAB3GAP2 orthologues in Danio rerio embryos and demonstrated that, whereas developmental expression of rab3gap1 was generalized (similar to that reported elsewhere in mice), rab3gap2 expression was restricted to the central nervous system. These findings are consistent with RAB3GAP2 having a key role in neurodevelopment and may indicate that Warburg micro and Martsolf syndromes represent a spectrum of disorders. However, we did not detect RAB3GAP2 mutations in patients with Warburg micro syndrome. These findings suggest that RAB3GAP dysregulation may result in a spectrum of phenotypes that range from Warburg micro syndrome to Martsolf syndrome.

MICRO syndrome: an entity distinct from COFS syndrome

Children born with the findings of microcephaly, cataracts and microcornea can result not only from a prenatal viral infection, but also from an autosomal recessive Mendelian disorders. We present three pairs of affected siblings with MICRO syndrome, who were born with congenital microcephaly, microcornea, and cataracts. MICRO syndrome is an autosomal recessive syndrome consisting of congenital microcephaly, cortical dysplasia, microcornea, cataracts, optic atrophy, severe mental retardation, hypotonic diplegia, and hypogenitalism. At birth, MICRO syndrome resembles Cerebro-Oculo-Facio-Skeletal (COFS) syndrome, but it differs in the lack of the rapidly progressive neurologic features leading to severe brain atrophy with calcifications. Patients with MICRO syndrome manifest frontal cortical dysplasia, hypoplasia of the corpus callosum, cortical blindness with optic atrophy, profound mental retardation, and progressive joint contractures with growth failure. COFS syndrome shares also many clinical and cellular similarities with Cockayne syndrome (CS), and cultured cells in both conditions demonstrate hypersensitivity to ultraviolet (UV) radiation due to impaired nucleotide excision repair (NER). NER studies in cultured fibroblasts from MICRO patients give normal results, so MICRO syndrome should be considered in children with features resembling COFS syndrome and CS, but who have normal NER. MICRO should be distinguished from other similar clinical disorders with normal NER by the presence of significant visual impairment and cortical blindness despite early surgery for congenital cataracts, frontal polymicrogyria, thin corpus callosum, and cortical atrophy by MRI.

Cerebro-oculo-facio-skeletal syndrome with a nucleotide excision-repair defect and a mutated XPD gene, with prenatal diagnosis in a triplet pregnancy

Cerebro-oculo-facio-skeletal (COFS) syndrome is a recessively inherited rapidly progressive neurologic disorder leading to brain atrophy, with calcifications, cataracts, microcornea, optic atrophy, progressive joint contractures, and growth failure. Cockayne syndrome (CS) is a recessively inherited neurodegenerative disorder characterized by low to normal birth weight, growth failure, brain dysmyelination with calcium deposits, cutaneous photosensitivity, pigmentary retinopathy and/or cataracts, and sensorineural hearing loss. Cultured CS cells are hypersensitive to UV radiation, because of impaired nucleotide-excision repair (NER) of UV-induced damage in actively transcribed DNA, whereas global genome NER is unaffected. The abnormalities in CS are caused by mutated CSA or CSB genes. Another class of patients with CS symptoms have mutations in the XPB, XPD, or XPG genes, which result in UV hypersensitivity as well as defective global NER; such patients may concurrently have clinical features of another NER syndrome, xeroderma pigmentosum (XP). Clinically observed similarities between COFS syndrome and CS have been followed by discoveries of cases of COFS syndrome that are associated with mutations in the XPG and CSB genes. Here we report the first involvement of the XPD gene in a new case of UV-sensitive COFS syndrome, with heterozygous substitutions-a R616W null mutation (previously seen in patients in XP complementation group D) and a unique D681N mutation-demonstrating that a third gene can be involved in COFS syndrome. We propose that COFS syndrome be included within the already known spectrum of NER disorders: XP, CS, and trichothiodystrophy. We predict that future patients with COFS syndrome will be found to have mutations in the CSA or XPB genes, and we document successful use of DNA repair for prenatal diagnosis in triplet and singleton pregnancies at risk for COFS syndrome. This result strongly underlines the need for screening of patients with COFS syndrome, for either UV sensitivity or DNA-repair abnormalities.

JM, Greenberg CR, Busch DB, Doughty ATB, Ziffer DW, Coleman DM, Savre-Train I, Friedberg EC. Manitoba aboriginal kindred with original cerebro-oculo- facio-skeletal syndrome has a mutation in the Cockayne syndrome group B (CSB) gene

Cerebro-oculo-facio-skeletal (COFS) syndrome is a rapidly progressive neurological disorder leading to brain atrophy with calcification, cataracts, microcornea, optic atrophy, progressive joint contractures, and growth failure. Cockayne syndrome (CS) is a recessively inherited neurodegenerative disorder characterized by low-to-normal birth weight; growth failure; brain dysmyelination with calcium deposits; cutaneous photosensitivity; pigmentary retinopathy, cataracts, or both; and sensorineural hearing loss. CS cells are hypersensitive to UV radiation because of impaired nucleotide excision repair of UV radiation-induced damage in actively transcribed DNA. The abnormalities in CS are associated with mutations in the CSA or CSB genes. In this report, we present evidence that two probands related to the Manitoba Aboriginal population group within which COFS syndrome was originally reported have cellular phenotypes indistinguishable from those in CS cells. The identical mutation was detected in the CSB gene from both children with COFS syndrome and in both parents of one of the patients. This mutation was also detected in three other patients with COFS syndrome from the Manitoba Aboriginal population group. These results suggest that CS and COFS syndrome share a common pathogenesis.

Congenital cataract and multisystem disorders

A knowledge of those syndromes associated with congenital cataract is essential for the paediatric ophthalmologist, as congenital cataracts are manifest in a large number of syndromes. It is important to have the correct diagnosis in such cases, not only for genetic and prognostic information, but also in order to help the parents to understand their child's condition. This paper describes the more common syndromes seen in association with congenital cataract, and emphasises the importance of looking at the whole child and family. We aim to provide a practical clinical guide to the diagnosis of hereditary and non-hereditary syndromes associated with congenital cataract.

Cataract, hypertrichosis, and mental retardation (CAHMR): a new autosomal recessive syndrome

We have studied 2 Egyptian sibs (the offspring of normal first cousins) with congenital cataract, hypertrichosis, mental retardation, and normal chromosomes. Review showed that the condition of our patients was not similar to any previously reported entity. POSSUM lists 84 syndromes with any of the above 3 main traits. Two disorders with cataract and mental retardation, Martsolf syndrome and Mollica-Pavone-Anterer syndrome, have overlapping manifestations and therefore are particularly differentiated from our cases. We suggest that the association of congenital cataract, hypertrichosis, and mental retardation observed in this report represents a new autosomal recessive syndrome.

Microcephaly, mental retardation, cataracts, and hypogonadism in sibs: Martsolf's syndrome

The association of microcephaly, mental retardation, cataracts, and hypogonadism is described in sibs (brother and sister) of consanguineous parents. These features are consistent with a diagnosis of Martsolf's syndrome. In addition, one sib had a cardiomyopathy while the other had cardiac failure.

Martsolf syndrome in a brother and sister: clinical features and pattern of inheritance

A brother and sister with Martsolf syndrome are reported. The main characteristics of the syndrome are mental retardation, short stature, cataracts, hypogonadism and craniofacial anomalies including microcephaly, maxillary retrusion, pouting mouth, malaligned teeth and mildly dysplastic pinnae. The metacarpal and phalangeal bones are short. The occurrence of Martsolf syndrome in sibs of opposite sex suggests autosomal recessive inheritance.

Martsolf's syndrome in a non-Jewish boy

Martsolf's syndrome has been described in Jewish people. We describe a patient of non-Jewish ancestry who has minor differences from other patients. The possible pattern of inheritance is discussed.

New syndromes from old: evaluation of heterogeneity and variability in syndrome definition and delineation

In 1969, McKusick discussed the nosology of genetic disease and the importance of considering heterogeneity and variability. Those considerations are still important today in that new syndromes are being described at the rate of one or more per week. However, often a "new" syndrome actually represents variable expression of a previously described condition; at other times, a child is reported as having a variant of a previously described syndrome when in reality that child has a distinct condition. The concepts of variability and heterogeneity will be discussed in the context of recently described findings in some "old" syndromes, thus shedding new light on them.