NGS-driven molecular diagnosis of heterogeneous hereditary neurological disorders reveals novel and known variants in disease-causing genes.

Hereditary neurological disorders (HNDs) are a clinically and genetically heterogeneous group of disorders. These disorders arise from the impaired function of the central or peripheral nervous system due to aberrant electrical impulses. More than 600 various neurological disorders, exhibiting a wide spectrum of overlapping clinical presentations depending on the organ(s) involved, have been documented. Owing to this clinical heterogeneity, diagnosing these disorders has been a challenge for both clinicians and geneticists and a large number of patients are either misdiagnosed or remain entirely undiagnosed. Contribution of genetics to neurological disorders has been recognized since long; however, the complete picture of the underlying molecular bases are under-explored. The aim of this study was to accurately diagnose 11 unrelated Pakistani families with various HNDs deploying NGS as a first step approach. Using exome sequencing and gene panel sequencing, we successfully identified disease-causing genomic variants these families. We report four novel variants, one each in, ECEL1, NALCN, TBR1 and PIGP in four of the pedigrees. In the rest of the seven families, we found five previously reported pathogenic variants in POGZ, FA2H, PLA2G6 and CYP27A1. Of these, three families segregate a homozygous 18 bp in-frame deletion of FA2H, indicating a likely founder mutation segregating in Pakistani population. Genotyping for this mutation can help low-cost population wide screening in the corresponding regions of the country. Our findings not only expand the existing repertoire of mutational spectrum underlying neurological disorders but will also help in genetic testing of individuals with HNDs in other populations.

Genetic analysis of osteopetrosis in Pakistani families identifies novel and known sequence variants.

Osteopetrosis is a genetically heterogenous, fatal bone disorder characterized by increased bone density. Globally, various genetic causes are reported for osteopetrosis with all forms of inheritance patterns. A precise molecular diagnosis is necessary for prognosis and for prescribing treatment paradigms in osteopetrosis. Here we report on thirteen individuals diagnosed with infantile malignant osteopetrosis coming from ten unrelated Pakistani families; nine of whom are consanguineous. We performed whole exome sequencing and Sanger sequencing in all families and identified homozygous variants in genes previously reported for autosomal recessive inheritance of osteopetrosis. All the identified variants are expected to affect the stability or length of gene products except one nonsynonymous missense variant. TCIRG1 was found as a candidate causal gene in majority of the families. We report six novel variants; four in TCIRG1 and one each in CLCN7 and OSTM1. Our combined findings will be helpful in molecular diagnosis and genetic counselling of patients with osteopetrosis particularly in populations with high consanguinity.

Hereditary brain tumor with a homozygous germline mutation in PMS2: pedigree analysis and prenatal screening in a family with constitutional mismatch repair deficiency (CMMRD) syndrome.

Precise genetic counseling and prenatal diagnosis are often hindered by incomplete penetrance of risk variance and complex patterns of inheritance. Here, we performed a clinical and genetic study of a five-generation Pakistani family with a history of multiple cases of childhood brain tumors. Six affected individuals died of brain tumors at very early ages and three were confirmed as having a homozygous mutation in exon 6 of the PMS2 gene (c.543delT). Fifteen members of the family were identified as heterozygous carriers of this mutation with a lack of cancer incidence. Both clinical manifestations and genetic test results of brain tumor patients in the family support the diagnosis of constitutional mismatch repair deficiency (CMMRD) syndrome, a condition in which individuals carry homozygous germline mutations in mismatch repair machinery genes with an early onset of malignancies such as glioma. This information was used to guide prenatal diagnosis with genetic testing on chorionic villus samples for the family. This is the first report of prenatal genetic diagnosis of hereditary brain tumor.

Whole exome sequencing identifies LRP1 as a pathogenic gene in autosomal recessive keratosis pilaris atrophicans.

BACKGROUND: Keratosis pilaris atrophicans (KPA) is a group of rare genodermatoses characterised by perifollicular keratosis and inflammation that progresses to atrophy and scars of the facial skin. Keratosis pilaris of extensor areas of limbs is a common associated finding. Most cases with KPA are sporadic and no consistent inheritance pattern has been documented. METHODS: A large consanguineous Pakistani pedigree segregating autosomal recessive KPA of a mixed type was subject to autozygosity mapping and whole exome sequencing. Quantification of mRNA and protein levels was performed on fibroblasts from affected individuals. Cellular uptake of the low-density lipoprotein (LDL) receptor-related protein 1 (LRP1) ligand α2-macroglobulin (α(2)M) was quantified using fluorescence confocal microscopy. RESULTS: Genetic analyses identified a unique homozygous missense variant (K1245R) in the LRP1 in all affected family members. LRP1 encodes the LRP1, a multifunctional cell surface receptor with endocytic functions that belongs to the LDL receptor family. The LRP1 mRNA and LRP1 protein levels in fibroblasts of affected individuals were markedly reduced when compared with controls. Similarly, the LRP1-mediated cellular uptake of α(2)M was reduced in patient fibroblasts. CONCLUSIONS: This is the first report on LRP1 as a pathogenic gene for autosomal recessive KPA and keratosis pilaris. The inflammatory characteristics of the KPA entity in our family suggest a link to the immune-regulatory functions of LRP1.

Exome sequencing circumvents missing clinical data and identifies a BSCL2 mutation in congenital lipodystrophy.

BACKGROUND: Exome sequencing has become more and more affordable and the technique has emerged as an important diagnostic tool for monogenic disorders at early stages of investigations, in particular when clinical information is limited or unspecific as well as in cases of genetic heterogeneity. METHODS: We identified a consanguineous Pakistani family segregating an autosomal recessive phenotype characterized by muscular hypertrophy, mild mental retardation and skeletal abnormalities. The available clinical information was incomplete and we applied whole exome sequencing in an affected family member for the identification of candidate gene variants. RESULTS: Exome sequencing identified a previously unreported homozygous mutation in the acceptor splice site of intron 5 in the BSCL2 gene (c.574-2A > G). Expression analysis revealed that the mutation was associated with skipping of exon 6. BSCL2 mutations are associated with Berardinelli-Seip congenital lipodystrophy and a clinical re-evaluation of affected individuals confirmed the diagnosis. CONCLUSIONS: Exome sequencing is a powerful technique for the identification of candidate gene variants in Mendelian traits. We applied this technique on a single individual affected by a likely autosomal recessive disorder without access to complete clinical details. A homozygous and truncating mutation was identified in the BSCL2 gene suggesting congenital generalized lipodystrophy. Incomplete phenotypic delineations are frequent limiting factors in search for a diagnosis and may lead to inappropriate care and follow-up. Our study exemplifies exome sequencing as a powerful diagnostic tool in Mendelian disorders that may complement missing clinical information and accelerate clinical diagnosis.

Autosomal recessive transmission of a rare KRT74 variant causes hair and nail ectodermal dysplasia: allelism with dominant woolly hair/hypotrichosis.

Pure hair and nail ectodermal dysplasia (PHNED) comprises a heterogeneous group of rare heritable disorders characterized by brittle hair, hypotrichosis, onychodystrophy and micronychia. Autosomal recessive (AR) PHNED has previously been associated with mutations in either KRT85 or HOXC13 on chromosome 12p11.1-q14.3. We investigated a consanguineous Pakistani family with AR PHNED linked to the keratin gene cluster on 12p11.1 but without detectable mutations in KRT85 and HOXC13. Whole exome sequencing of affected individuals revealed homozygosity for a rare c.821T>C variant (p.Phe274Ser) in the KRT74 gene that segregates AR PHNED in the family. The transition alters the highly conserved Phe274 residue in the coil 1B domain required for long-range dimerization of keratins, suggesting that the mutation compromises the stability of intermediate filaments. Immunohistochemical (IHC) analyses confirmed a strong keratin-74 expression in the nail matrix, the nail bed and the hyponychium of mouse distal digits, as well as in normal human hair follicles. Furthermore, hair follicles and epidermis of an affected family member stained negative for Keratin-74 suggesting a loss of function mechanism mediated by the Phe274Ser substitution. Our observations show for the first time that homozygosity for a KRT74 missense variant may be associated with AR PHNED. Heterozygous KRT74 mutations have previously been associated with autosomal dominant woolly hair/hypotrichosis simplex (ADWH). Thus, our findings expand the phenotypic spectrum associated with KRT74 mutations and imply that a subtype of AR PHNED is allelic with ADWH.

Evidence for autosomal recessive inheritance in SPG3A caused by homozygosity for a novel ATL1 missense mutation.

Hereditary spastic paraplegias (HSPs) comprise a heterogeneous group of disorders characterized by progressive spasticity and weakness of the lower limbs. Autosomal dominant and 'pure' forms of HSP account for ∼80% of cases in Western societies of whom 10% carry atlastin-1 (ATL1) gene mutations. We report on a large consanguineous family segregating six members with early onset HSP. The pedigree was compatible with both autosomal dominant and autosomal recessive inheritance. Whole-exome sequencing and segregation analysis revealed a homozygous novel missense variant c.353G>A, p.(Arg118Gln) in ATL1 in all six affected family members. Seven heterozygous carriers, five females and two males, showed no clinical signs of HSP with the exception of sub-clinically reduced vibration sensation in one adult female. Our combined findings show that homozygosity for the ATL1 missense variant remains the only plausible cause of HSP, whereas heterozygous carriers are asymptomatic. This apparent autosomal recessive inheritance adds to the clinical complexity of spastic paraplegia 3A and calls for caution using directed genetic screening in HSP.

Cenani-Lenz syndrome restricted to limb and kidney anomalies associated with a novel LRP4 missense mutation.

Cenani-Lenz syndrome (CLS) is a rare autosomal recessive developmental disorder of the limbs. The disorder is characterized by complete syndactyly with metacarpal fusions and/or oligodactyly sometimes accompanied by radioulnar synostosis. The clinical expression is variable and kidney agenesis/hypoplasia, craniofacial dysmorphism and teeth abnormalities are frequent features as well as lower limb involvement. CLS was recently associated with mutations in the low-density lipoprotein receptor-related protein 4 (LRP4) gene and dysregulated canonical WNT signaling. We have identified a large consanguineous Pakistani pedigree with 9 members affected by CLS. The affected individuals present with a consistent expression of the syndrome restricted to the limbs and kidneys. Symptoms from the lower limb are mild or absent and there were no radioulnar synostosis or craniofacial involvement. Genetic analysis using autozygosity mapping and sequencing revealed homozygosity for a novel missense mutation c.2858T > C (p.L953P) in the LRP4 gene. The mutation is located in a region encoding the highly conserved low-density lipoprotein receptor repeat class B domain of LRP4. Our findings add to the genotype-phenotype correlations in CLS and support kidney anomalies as a frequent associated feature.

Novel missense mutation in the RSPO4 gene in congenital hyponychia and evidence for a polymorphic initiation codon (p.M1I).

BACKGROUND: Anonychia/hyponychia congenita is a rare autosomal recessive developmental disorder characterized by the absence (anonychia) or hypoplasia (hyponuchia) of finger- and/or toenails frequently caused by mutations in the R-spondin 4 (RSPO4) gene. METHODS: Three hypo/anonychia consanguineous Pakistani families were ascertained and genotyped using microsatellite markers spanning the RSPO4 locus on chromosome 20p13. Mutation screening of the RSPO4 gene was carried out by direct sequencing of the entire coding region and all intron-exon boundaries. RESULTS: Mutations in the RSPO4 gene were identified in all families including a novel missense mutation c.178C>T (p.R60W) and two recurrent variants c.353G>A (p.C118Y) and c.3G>A (p.M1I). The c.3G>A variant was identified in unaffected family members and a control sample in a homozygous state. CONCLUSIONS: This study raises to 17 the number of known RSPO4 mutations and further expands the molecular repertoire causing hypo/anonychia. The c.353G>A emerges as a recurrent change with a possible founder effect in the Pakistani population. Our findings suggest that c.3G>A is not sufficient to cause the disorder and could be considered a polymorphism.

ß-Thalassemia in Pakistan: a pilot program on prenatal diagnosis in Multan.

Prenatal diagnosis (PND) of ß-thalassemia has been underutilized in Pakistan because of a number of social and economic factors. National Institute for Biotechnology and Genetic Engineering Faisalabad in collaboration with Multan Institute of Nuclear Medicine and Radiotherapy Multan introduced free PND service for carrier couples of Multan district. Multan has a population of about 4 million. More than 170 couples registered for retrospective PND and in 2 years 105 PND were carried out through first trimester chorionic villus sampling. Almost 90% of these couples were unable to afford the cost of PND and would not have undergone the test as free service was not available. Monoplex and Multiplex Amplification Refractory Mutation System-polymerase chain reaction and genomic DNA sequencing were used for detection of IVS (intervening sequence)-I-5 (G-C), FSC (frameshift codon)-8/9 (+G), FSC-41/42 (-TTCT), IVS-I-1 (G-T), 619 bp deletion, and CD-15 (G-A) ß-globin mutations. Eighty-one percent (85/105) couples analyzed were in a consanguineous marriage. Twenty-three fetuses were found homozygous mutant and all couples opted for discontinuation of affected pregnancies. More families are registering for PND after establishment of this free and accessible PND service.

Gastric tuberculosis with concomitant stromal tumour of stomach (GIST).

Gastric tuberculosis is an extremely rare condition because of unfavorable circumstances in stomach due to low pH, high motility and lack of lymphoid tissue. All these discourage the development of tuberculous lesion. Similarly, simultaneous stromal tumour of stomach is also a rare entity. We present a rare case of tuberculosis of stomach with no evidence of pulmonary involvement and a concomitant stromal tumour of the stomach. This unique case illustrates the need for a high index of suspicion in order to diagnose this rare condition, as this can present in patients with no particular risk factors or minimal symptoms.