Recently, CASK aberrations caused by both mutations and deletions have been reported to cause severe mental retardation (MR), microcephaly and disproportionate pontine and cerebellar hypoplasia (MICPCH) in females.
The NDP deletion could account for the exudative retinopathy and the CASK deletion for the microcephaly, while CASK and KDM6A have both been associated with coloboma.
Heterozygous loss of function mutations of CASK at Xp11.4 in females cause severe intellectual disability (ID) and microcephaly with pontine and cerebellar hypoplasia (MICPCH).
CASK mutations have been reported in patients with intellectual disability with microcephaly and pontocerebellar hypoplasia or congenital nystagmus, and those with FG syndrome.
The comparison of the clinical features between the 19 SLC2A1 mutated and the 226 non-mutated patients revealed that the onset of epilepsy within the first year of life (when associated with developmental delay or other neurological manifestations), the association of epilepsy with PD and acquired microcephaly are more common in mutated subjects.
Glucose transporter type 1 deficiency syndrome (Glut-1DS) is caused by autosomal dominant haplodeficiency or autosomal recessive with homozygous mutation of the glucose transporter 1 (SLC2A1) gene and is characterized by severe seizures, developmental delay, ataxia and acquired microcephaly.
Mutations in SLC2A1, encoding the glucose transporter type 1 (Glut1), cause a wide range of neurological disorders: (1) classical Glut1 deficiency syndrome (Glut1-DS) with an early onset epileptic encephalopathy including a severe epilepsy, psychomotor delay, ataxia and microcephaly, (2) paroxysmal exercise-induced dyskinesia (PED) and (3) various forms of idiopathic/genetic generalized epilepsies such as different forms of absence epilepsies.
Here we present an unusual case of DNA ligase IV deficiency syndrome without dysmorphic facial findings and microcephaly complicated with Epstein-Barr virus-associated large B-cell lymphoma with the right lung involvement and a massive brain tumor lesion in a two-year-old female.
Mutations of Lig4 are exclusively hypomorphic and have only been described in six patients, four exhibiting mild immunodeficiency associated with microcephaly and developmental delay, while two patient had leukemia.
This work extends the phenotypic spectrum associated with LIG4 mutations, establishing that extreme growth retardation with microcephaly is a common presentation of bilallelic truncating mutations.
Hypomorphic LIG4 mutations in humans are associated with increased cellular radiosensitivity, microcephaly, facial dysmorphisms, growth retardation, developmental delay, and a variable degree of immunodeficiency.
Patient 2, homozygous for a frameshift variant (p.Ala429Thrfs*42), presented a phenotype partially consistent with MCSZ including microcephaly and developmental delay, but without seizures.
One of the syndromic forms of microcephaly is microcephaly, seizures and developmental delay (MCSZ) (OMIM #613402), a rare autosomal recessive neurodevelopmental disorder with a range of phenotypic severity, and known to be caused by mutations in the polynucleotide kinase 3' phosphatase (PNKP) gene.
Mutations in TDP1 and APTX have been linked to Spinocerebellar ataxia with axonal neuropathy (SCAN1) and Ataxia-ocular motor apraxia 1 (AOA1), respectively, while mutations in PNKP are considered to be responsible for Microcephaly with seizures (MCSZ) and Ataxia-ocular motor apraxia 4 (AOA4).
Novel truncating mutations in the polyglutamine tract binding protein 1 gene (PQBP1) cause Renpenning syndrome and X-linked mental retardation in another family with microcephaly.
Here we show that a homozygous mutation affecting a highly conserved MFSD2A residue (p.Ser339Leu) is associated with a progressive microcephaly syndrome characterized by intellectual disability, spasticity and absent speech.
Two new studies show that inactivating mutations in MFSD2A, known to be expressed specifically at the blood-brain barrier, lead to microcephaly, thereby offering a simple and surprising solution to an old enigma.
Recent studies have implicated MFSD2A mutations in lethal and non-lethal microcephaly syndromes, with the severity correlating to the residual activity of the transporter.
Of the genes in that region, we propose that SLC9A6 is the most likely to play an important role as mutations in this gene lead to Christianson syndrome, in which patients may have microcephaly and weight loss.
Mutations in SLC9A6 are associated with Christianson syndrome (OMIM 300243), a syndromic form of X-linked mental retardation (XLMR) characterized by microcephaly, severe global developmental delay, ataxia and seizures.