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PubMed2005

The first missense alteration in the MCPH1 gene causes autosomal recessive microcephaly with an extremely mild cellular and clinical phenotype.

Autosomal recessive primary microcephaly (MCPH) is a rare neurodevelopmental disorder characterized by mental retardation and congenital microcephaly with a head circumference at least 4 SD below age and sex means, in the absence of other significant malformations or neurological deficits. Truncating alterations in the MCPH1 gene have previously been shown to exhibit a distinct cellular phenotype, with a high proportion of prophase-like cells (>10%) due to premature chromosome condensation in early G2- and delayed decondensation in early G1-phase of the cell cycle. We report here the first patient with a homozygous substitution of a highly conserved threonine residue by an arginine (c.80C>G, Thr27Arg) localized in the N-terminal BRCT domain of MCPH1. The cellular and clinical phenotype of this patient is much less pronounced than that of previously described patients with truncating alterations in the MCPH1 gene. Firstly, the fraction of prophase-like cells accounts for just 3-4% of the cell population. Secondly, clinically, he has only a very mild mental retardation with predominantly delayed motor skills but normal verbal IQ attainment. Additionally, head circumference was less severely affected, being -2.4 SD at birth and -3 SD at the age of six years. This justifies reconsideration and widening of the clinical phenotype definition of MCPH1.

Amino Acid Sequence↗

PubMed2025

Loss-of-Function CARS1 Variants in a Patient With Microcephaly, Developmental Delay, and a Brittle Hair Phenotype.

BACKGROUND: Mutations in cysteinyl-tRNA synthetase (CARS1) have been implicated in a multisystem disease including microcephaly, developmental delay, and brittle hair and nail phenotypes. METHODS: Here, we present a patient with hepatopathy, hypothyroidism, short stature, developmental delay, microcephaly, muscular hypotonia, brittle hair, and ataxia. The patient underwent exome sequencing to identify potentially pathogenic genetic variants. In addition, identified variants were assessed using yeast complementation assays to determine functional consequences. RESULTS: Exome sequencing determined that the patient is compound heterozygous for p.Arg341His and p.Arg370Trp CARS1. Yeast complementation assays showed that the p.Arg341His variant has a hypomorphic effect and that the p.Arg370Trp variant causes a complete loss-of-function effect. CONCLUSION: This study is the second report of pathogenic CARS1 variants and expands the allelic and phenotypic heterogeneity of CARS1-associated disease.

Humans↗

PubMed1984

Genetic microcephaly in a pair of monozygous twins.

A pair of monozygotic female twins with true primary microcephaly is described. The autosomal-recessive nature of the disease is supported by the following: the twins are concordant for the disease; the parents, themselves normal, are related; the reduced skull dimensions were noted at birth; neurologic problems are absent; the karyotype is normal; the gestation and delivery were normal, without any history of influences capable of inducing microcephaly. A detailed dermatoglyphic study is given.

Consanguinity↗

PubMed1987

Congenital microcephaly, infantile spasms, psychomotor retardation, and nephrotic syndrome in two sibs.

Two boys are described with congenital microcephaly, infantile spasms, psychomotor retardation and an early-onset nephrotic syndrome. The autopsy findings of one patient are described in detail. Polymicrogyria was the most prominent feature and the kidneys showed focal segmental glomerulosclerosis. These findings have been described as a clinical entity, the leading symptoms being congenital microcephaly, early-onset nephrotic syndrome and mental retardation, accompanied by various other clinical symptoms. A review of the literature suggests an autosomal recessive mode of inheritance.

Atrophy↗

PubMed1995

Microcephaly and early-onset nephrotic syndrome--confusion in Galloway-Mowat syndrome.

We report a 2-year-old girl with nephrotic syndrome, microcephaly, seizures and psychomotor retardation. Histological studies of a renal biopsy revealed focal glomerular sclerosis with mesangiolysis and capillary microaneurysms. Dysmorphic features were remarkable: abnormal-shaped skull, coarse hair, narrow forehead, large low-set ears, almond-shaped eyes, low nasal bridge, pinched nose, thin lips and micrognathia. Cases with this rare combination of microcephaly and early onset of nephrotic syndrome with various neurological abnormalities have been reported. However, clinical manifestations and histological findings showed a wide variation, and there is a lot of confusion in this syndrome. We therefore reviewed the previous reports and propose a new classification of this syndrome.

Child, Preschool↗

PubMed1998

Abnormal development of serotonin nerve fibers in the visual cortex in rats with methylazoxymethanol-induced microcephaly.

The postnatal development of serotonin (5HT)-immunoreactive axons was studied in the visual cortex of the cerebrum in both normal and microcephalic rats during early postnatal and young adult stages. Severe microcephaly in rat offspring was induced by prenatal exposure to methylazoxymethanol acetate (MAM), an anti-mitotic agent, on day 15 of gestation. From postnatal day 1 (PND 1) to PND 5, fine and short 5HT fibers were irregularly dispersed throughout the occipital cortex in both the control and MAM-treated rats (MAM-rats). A conspicuous aggregation of dot-like 5HT terminals was found in controls, but not in MAM-rats, in a shallow layer of the dorsomedial region of the occipital cortical plate. On PND 7, such an aggregation of 5HT terminals was found in both groups. The density of the aggregation increased up to PND 9, but then decreased gradually, finally becoming unrecognizable at around PND 15 in both groups. MAM-rats, however, always showed hyperaggregation of 5HT terminals when compared with controls on the same PND. The density of 5HT fibers gradually increased, and finally made up a network-like formation at PND 28 in both groups, its pattern was essentially identical to the abnormal distribution of 5HT fibers during the later stage. As a result, the network-like formation of 5HT fibers in the MAM-rats at PND 28 was markedly twisted and somewhat hyperdense. In Nissl-stained preparations from PND 9 to 15, the 5HT terminal aggregation in the control rats was precisely confined to the newly forming layer IV of the visual cortex. In the MAM-rats, on the other hand, the aggregation of 5HT terminals was not associated with a specific cortical layer because of a disarranged cytoarchitecture of the microcephaly.

Animals↗

PubMed2005

SNP array-based homozygosity mapping reveals MCPH1 deletion in family with autosomal recessive mental retardation and mild microcephaly.

Very little is known about the molecular basis of autosomal recessive MR (ARMR) because in developed countries, small family sizes preclude mapping and identification of the relevant gene defects. We therefore chose to investigate genetic causes of ARMR in large consanguineous Iranian families. This study reports on a family with six mentally retarded members. Array-based homozygosity mapping and high-resolution microarray-based comparative genomic hybridization (array CGH) revealed a deletion of approximately 150-200 kb, encompassing the promoter and the first six exons of the MCPH1 gene, one out of four genes that have been previously implicated in ARMR with microcephaly. Reexamination of affected individuals revealed a high proportion of prematurely condensed chromosomes, which is a hallmark of this condition, but in spite of the severity of the mutation, all patients showed only borderline to mild microcephaly. Therefore the phenotypic spectrum of MCPH1 mutations may be wider than previously assumed, with ARMR being the only consistent clinical finding.

Adolescent↗

PubMed1999

Syndrome of microcephaly, Dandy-Walker malformation, and Wilms tumor caused by mosaic variegated aneuploidy with premature centromere division (PCD): report of a new case and review of the literature.

We report a male infant with multiple congenital anomalies and mosaic variegated aneuploidy; a rare cytogenetic abnormality characterized by mosaicism for several different aneuploidies involving many different chromosomes. He had prenatal-onset growth retardation, microcephaly, dysmorphic face, seizures, hypotonia, feeding difficulty, and developmental delay. In addition, he developed bilateral Wilms tumors. Neuroradiological examination revealed Dandy-Walker malformation and hypoplasia of the cerebral hemisphere and pons. Cytogenetic analysis revealed various multiple numerical aneuploidies in blood lymphocytes, fibroblasts, and bone marrow cells, together with premature centromere division (PCD). Peripheral blood chromosome analysis from his parents also showed PCD, but no aneuploid cells. The clinical phenotype and multiple aneuploidies of the patient may be a consequence of the homozygous PCD trait inherited from his parents. Comparison with previously reported cases of multiple aneuploidy suggests that mosaic variegated aneuploidy with PCD may be a clinically recognizable syndrome with major phenotypes being mental retardation, microcephaly, structural brain anomalies (including Dandy-Walker malformation), and possible cancer predisposition.

Abnormalities, Multiple↗

PubMed2006

Genetic studies of autosomal recessive primary microcephaly in 33 Pakistani families: Novel sequence variants in ASPM gene.

Human autosomal recessive primary microcephaly (MCPH) is a rare genetic disorder in which affected individuals are born with reduced brain size. MCPH is genetically heterogeneous, with six loci and four genes reported to date. Mutations in the ASPM gene at the MCPH5 locus appear to be the most common cause of MCPH. For this study, 33 Pakistani families with primary microcephaly were enrolled. Genotyping using microsatellite markers linked to the six known MCPH loci showed the linkage of 18 families to the MCPH5 locus, two to the MCPH2 locus, two to the MCPH4 locus, and one to the MCPH6 locus. The remaining ten families were not linked to any of the known loci. Families linked to the MCPH5 locus were further subjected to screening of the ASPM gene with direct DNA sequencing. Two previously reported variants, 3978G>A (W1326X) and 9557C>G (S3186X), were observed in five Pakistani families. Four novel nonsynonymous sequence variants, 9118insCATT, 9238A>T (L3080X), 9539A>C (Q3180P), and 1260delTCAAGTC, were found to segregate within four families, but were not observed in 200 Pakistani control chromosomes. One of the variants, 9539A>C (Q3180P), occurred in the IQ 79 domain, but its functional significance awaits definition.

Adolescent↗

PubMedDate not supplied

Impaired Biel and radial arm maze learning in rats with methylnitrosourea-induced microcephaly.

Jc1:SD rats were given methylnitrosourea (MNU; 5 mg/kg, IP) on day 13 of gestation. Male offspring with MNU-induced microcephaly were examined on the Biel water maze and its mirror-image maze at 6 weeks of age and on a radial eight-arm maze at 14 weeks of age. The MNU rats showed postnatal depression in body weight. Their brain weight was about 60% of the control value, and they were thus microcephalic. The MNU animals made significantly more errors on the Biel maze and its mirror-image maze than the controls. In the radial arm maze test, they required more trials to acquire the learning criterion than the controls, and the animals with the acquired learning criterion were fewer. In the retest, however, no significant difference appeared in number of trials required for reacquisition of the criterion between the MNU and control animals. The autopsy of the MNU animals revealed the thinned cerebral cortex and hypoplastic hippocampus. The present results with the MNU rats confirmed the learning impairment and suggested no effect of microcephaly on retention of the acquired memory.

Animals↗

PubMed2006

A case report of a patient with microcephaly, facial dysmorphism, mitomycin-c-sensitive lymphocytes, and susceptibility to lymphoma.

We report on a 17-year-old boy with a unique lymphocyte mitomycin-C (MMC)-sensitive chromosomal breakage syndrome. He had failure to thrive, and has microcephaly, slight facial dysmorphism, and constitutional short stature but no other phenotypic or hematological manifestations of Fanconi anemia (FA). He developed B-cell lymphoma of the neck, which was treated with standard doses of alkylating agents. Major side effects related to chemotherapy did not occur. Normal erythrocyte corpuscular volume, MMC-insensitive fibroblasts, and the occurrence of lymphoma rather than AML sets this patient apart from typical FA. The combination of constitutional dwarfism, microcephaly, MMC-sensitive lymphocytes, and susceptibility to lymphoma represents an unusual constellation of symptoms among genetic disorders.

Adolescent↗

PubMed2003

What's new in neurogenetics? Focus on "primary microcephaly".

Primary microcephaly is a specific form of microcephaly that is inherited in an autosomal recessive manner. Six loci have been mapped for this condition and the genes at two of these loci have recently been identified. These include the Microcephalin gene at the MCPH1 locus and the ASPM gene at the MCPH5 locus.

Cell Cycle Proteins↗

PubMed2005

Evolution of primary microcephaly genes and the enlargement of primate brains.

Brain size, in relation to body size, has varied markedly during the evolution of mammals. In particular, a large cerebral cortex is a feature that distinguishes humans from our fellow primates. Such anatomical changes must have a basis in genetic alterations, but the molecular processes involved have yet to be defined. However, recent advances from the cloning of two human disease genes promise to make inroads in this important area. Microcephalin (MCPH1) and Abnormal spindle-like microcephaly associated (ASPM) are genes mutated in primary microcephaly, a human neurodevelopmental disorder. In this 'atavistic' condition, brain size is reduced in volume to a size comparable with that of early hominids. Hence, it has been proposed that these genes evolved adaptively with increasing primate brain size. Subsequent studies have lent weight to this hypothesis by showing that both genes have undergone positive selection during great ape evolution. Further functional characterisation of their proteins will contribute to an understanding of the molecular and evolutionary processes that have determined human brain size.

Animals↗

PubMed2024

Loss-of-function in RBBP5 results in a syndromic neurodevelopmental disorder associated with microcephaly.

PURPOSE: Epigenetic dysregulation has been associated with many inherited disorders. RBBP5 (HGNC:9888) encodes a core member of the protein complex that methylates histone 3 lysine-4 and has not been implicated in human disease. METHODS: We identify 5 unrelated individuals with de novo heterozygous variants in RBBP5. Three nonsense/frameshift and 2 missense variants were identified in probands with neurodevelopmental symptoms, including global developmental delay, intellectual disability, microcephaly, and short stature. Here, we investigate the pathogenicity of the variants through protein structural analysis and transgenic Drosophila models. RESULTS: Both missense p.(T232I) and p.(E296D) variants affect evolutionarily conserved amino acids located at the interface between RBBP5 and the nucleosome. In Drosophila, overexpression analysis identifies partial loss-of-function mechanisms when the variants are expressed using the fly Rbbp5 or human RBBP5 cDNA. Loss of Rbbp5 leads to a reduction in brain size. The human reference or variant transgenes fail to rescue this loss and expression of either missense variant in an Rbbp5 null background results in a less severe microcephaly phenotype than the human reference, indicating both missense variants are partial loss-of-function alleles. CONCLUSION: Haploinsufficiency of RBBP5 observed through de novo null and hypomorphic loss-of-function variants is associated with a syndromic neurodevelopmental disorder.

Humans↗

PubMed2004

Pyridoxine-dependent seizures and microcephaly.

Pyridoxine dependency is a rare autosomal-recessive disorder causing intractable seizures in neonates and infants. This case report describes an infant with pyridoxine-dependent seizures with microcephaly and discusses a probable pathogenetic mechanism of microcephaly in this condition.

Humans↗

PubMed2000

Association of epilepsy with different groups of microcephaly.

Sixty-six participants (33 males, 33 females) with microcephaly (MC), age range from 2 to 19 years old, were evaluated. MC was classified pathogenetically into isolated MC (IMC) and multiple MC (MMC) and classified etiologically into primary MC (PMC) and secondary MC (SMC). Both IMC and MMC were further classified. Overall prevalence of epilepsy was 40.9%. Furthermore, there was a significantly higher prevalence of epilepsy in males. Main seizure type was generalized tonic-clonic seizures. Generally, learning disability (LD) was diagnosed in 93.9% and profound LD was evident in 43.9% of participants. There was an inverse correlation between severity of epilepsy and IQ but a positive correlation between severity of epilepsy and degree of LD. Differences in the success rate between monotherapy and polytherapy or response to antiepileptic drugs were not observed. Results suggest that epilepsy may be associated with the lower cognitive ability of the participants with microcephaly. The pathogenetic classification proposed is of value in delineating the prevalence of epilepsy and LD in the different varieties of MC as compared with the etiological classification.

Adolescent↗

PubMed2002

Mutant deoxynucleotide carrier is associated with congenital microcephaly.

The disorder Amish microcephaly (MCPHA) is characterized by severe congenital microcephaly, elevated levels of alpha-ketoglutarate in the urine and premature death. The disorder is inherited in an autosomal recessive pattern and has been observed only in Old Order Amish families whose ancestors lived in Lancaster County, Pennsylvania. Here we show, by using a genealogy database and automated pedigree software, that 23 nuclear families affected with MCPHA are connected to a single ancestral couple. Through a whole-genome scan, fine mapping and haplotype analysis, we localized the gene affected in MCPHA to a region of 3 cM, or 2 Mb, on chromosome 17q25. We constructed a map of contiguous genomic clones spanning this region. One of the genes in this region, SLC25A19, which encodes a nuclear mitochondrial deoxynucleotide carrier (DNC), contains a substitution that segregates with the disease in affected individuals and alters an amino acid that is highly conserved in similar proteins. Functional analysis shows that the mutant DNC protein lacks the normal transport activity, implying that failed deoxynucleotide transport across the inner mitochondrial membrane causes MCPHA. Our data indicate that mitochondrial deoxynucleotide transport may be essential for prenatal brain growth.

Carrier Proteins↗

PubMed2002

MEHMO (Mental retardation, Epileptic seizures, Hypogenitalism, Microcephaly, Obesity): a new X-linked mitochondrial disorder.

MEHMO (Mental retardation, Epileptic seizures, Hypogenitalism, Microcephaly and Obesity) is an X-linked disorder characterised by mental retardation, epileptic seizures, hypogenitalism, microcephaly and obesity. It was recently assigned to the locus Xp21.1-p22.13. We describe a child with MEHMO and lactic acidosis whose muscle biopsy revealed markedly reduced activities of complexes 1,3 and 4 of the mitochondrial electron transport chain. Histological staining showed mitochondrial proliferation and lipid storage. Electron microscopy revealed abnormal and enlarged mitochondria with concentric cristae and electron dense bodies. This is the first identification of MEHMO as a mitochondrial disorder and one of the very few X-linked mitochondrial syndromes.

Abnormalities, Multiple↗