The development of human brain which occurs
throughout human life begins with the expansion of the neuro epithelium to produce
radial glial stem cells (RGs) (Cizkova
et al., 2012) which than split
up at the apical surface within the ventricular zone (VZ) to generate neurons
and intermediate progenitors. Intermediate progenitors populate the adjacent
sub ventricular zone (SVZ) whereas the neurons migrate through the intermediate
zone to occupy specific layers within the cortical plate (Fietz
et al., 2010; Hansen et al., 2010).
Measurement of head circumference known as occipital frontal circumference has
been used as an index to evaluate human brain size for many years. Measurements of HC in terms of percentiles or standard deviations (SDs) above or below the mean for the reference
populationare compared with standard references (Passemard et al., 2013;
Cooke et al., 1977).
One of the most significant unresolved
problems in health care is microcephaly (minor head), in which
the head circumference (HC) is decreased because of an inborn lack of fetal
brain development, especially affecting the cerebral cortex (Qazi and Reed,
1975; Mochida and Walsh, 2001).Microcephaly is a condition in which the head
circumference of an affected
individual is smaller than <3 SD below the mean for age.The small head in microcephaly is also associated with mental retardation in the affected individuals.On the other hand, severity of microcephaly also correlates with abnormalities of brain structure (Custer et al., 2000) as in both Microcephaly and Macrocephaly, head circumference values below the mean are linked with an elevated incidence of lower cerebral abilities. This means that small differences in head size could be significant in the interrelationship between head circumference,intelligence and learning (Olson and verki, 2003). Microcephaly is caused both by environmental and genetic factors. Environmental factors include intrauterine infections, drugs taken during pregnancy, prenatal radiation exposure, maternal phenylketonuria, and birth asphyxia while genetic mechanisms, include cytogenetic abnormalities, single-gene disorders, etc. (Baraitser, 1990; Qazi and Reed, 1973). The genetic factors that can cause isolated Microcephaly are mainly Mendelian autosomal dominant, recessive, or X linked genes (Pryor et al., 1968). According to time of occurrence Microcephaly is divided into primary Microcephaly,which is present at birth, and secondary Microcephaly, which develops postnatally (Woods, 2004). The important difference between these types is that primary Microcephaly is usually a steady developmental anomaly, while secondary Microcephaly is caused by a progressive neurodegenerative condition after birth. (Opitz and Holt 1992; Dobyns 2002; Rosenberg et al., 2002). Non-syndromic microcephaly is isolated with no other observable abnormalities while, in syndromic form microcephaly is connected with other abnormalities. With syndromic microcephaly, different ecological, chromosomal or single-gene abnormalities are also connected, while in case of Non syndromic, microcephaly is isolated and always etiologically heterogeneous (Woods, 2004). Microcephaly Primary Hereditary (MCPH) is a heritably varied neuro developmental disorder describe via a considerabily reduced head boundary present before by origin and brain disability (Passemard et al., 2010) MCPH patients show little head occurring or existing before birth with head circumference equivalent or less than (-2) standard deviation (SD) at birth and -3 SD at 1 year old, compared age-related mean. Because of mild-to-moderate intellectual impairment and short stature, in MCPH patient's brain enlargement and neurogenesis are affected and generally with lack of extra neurological or somatic abnormalities (Alcantara and O'Driscoll 2014; Barbelanne and Tsang 2014). In consanguineous residents such as Pakistani, the incidence of MCPH is up to 150/100,000 with about 200 families worldwide however MCPH is an occasional congenital disease, affecting about 1/100,000 in newborns(Bond et al., 2002). To date in MCPH patients seventeen MCPH loci have been recognized globaly. 68.6 % of MCPH is caused due to bi-allelic mutations in ASPM gene, 14.1 % is caused by WDR62 and MCPH1 gene as causative factor is responsible for 8% of MCPH. In western Europeans concerning 50 to 75% or North Americans with MCPH and in Pakistanis or Indians about 20 to 30% of MCPH still additional genetic loci are predictable to exist known to be deficient in mutations of recognized loci (Zaqout et al., 2017). The MCPH1 (Microcephalin 1) locus is identified on chromosome 8p23.1 (Ahmad et al., 2017; Jackson et al., 2002), MCPH2 (WD-repeat-containing protein 62) on 19q13.12 (Sajid et al., 2013), MCPH3 (Cyclin-dependent kinase 5 regulatory subunit-associated protein 2) on 9q33.2 (Issa et al.,2013),MCPH4 (Kinetochore-null gene 1) on 15q15.1 (Takimoto, 2017;Genin et al., 2012), MCPH5 (Abnormal spindle-like, microcephaly associated protein) on 1q31.3 (Ahmad et al., 2017;Pulvers et al., 2010), MCPH6 (Centromeric protein J) on 13q12.2 (Gul et al., 2006), MCPH7 (SCL/TAL1-interrupting locus protein) on 1p33 (Kakar et al., 2015),MCPH 8 (Centrosomal protein 135 kD) on 4q12 (Hussain et al., 2012), MCPH 9 (Centrosomal protein 152 kD) on 15q21.1 (Guernsey et al., 2010), MCPH10 (Zinc finger protein 335) on 20q13.12 (Yang et al., 2012), MCPH 11 (Polyhomeotic-like 1 protein) on 12p13.31 (Awad et al., 2013), MCPH 12 (Cyclin-dependent kinase 6) on 7q21.2 (Hussain et al., 2013), MCPH 13 (Centromeric protein E) on 4q24 (Mirzaa et al., 2014), MCPH 14 (SAS-6 centriolar assembly protein) on 1p21.2 (Khan et al., 2014), MCPH 15 (Major facilitator superfamily domain-containing protein 2A) on 1p34.2 (Alakbarzade et al., 2015), MCPH 16 (Ankyrin repeat- and LEM domain-containing protein 2) on 12q24.33 (Yamamoto et al., 2014) and MCPH 17 (Citron rho-interacting serine/threonine kinase) on 12q24.23 (Basit et al., 2016). MCPH is literally common and ASPM appears to exist the main MCPH gene with 95 different ASPM mutations reported so far in the Pakistani inhabitants (Muhammad et al., 2009; Nicholas et al., 2009; Kousar et al., 2010; Darvish et al., 2010). In relation of especially high occurrence of MCPH in Pakistan owing to consanguineous marriages with respect to compound heterozygosity only one case has been reported so far (Bond et al. 2003; Woods et al., 2005; Gul et al., 2006). In current study of MCPH disorder, two specific families are sampled from District Mardan, Khyber Pakhtunkhwa (KPK), Pakistan. Family A consists of five members with two affected male and one female. Family B consists of five members with one affected male and female respectively. Parents are normal in both families. Experimentation work carried out in Kohat University of science and technology (KUST), linked family A to Abnormal spindle-like,Microcephaly associated protein (ASPM) on chromosome number 1q31.3. No linkage was found in family B. Aims and Objectives The principal objectives of the study are; 1. Analysis of affected person of primary Microcephaly in Pakistani population. 2. Screening of MCPH genes for mutations to add the mutational spectra of these genes. 3. Identification of novel MCPH loci to underlying causal gene variants, to uncover novel genes functions and their role in etiology ofMCPH.