Mendelian disorders, also called monogenic disorders, arise due to mutations in a single gene, with minimum influence from the environment. The studies of these mutations have been providing important insights into functional characterization of the genome. Therefore, this knowledge is instrumental for making essential decisions and therapeutic interventions. Although, these diseases are very rare world-wide, they are observed more frequently in populations with cousin marriages. Pakistani population has high rates of consanguinity i.e. >76%, in which 80% couples are first cousins. Thus, this consanguineous population together with large and extended pedigree size provides a rich source for genetic/molecular studies of such inherited disorders. In this study, six families, segregating different Mendelian disorder each, were investigated using different approaches and techniques. Autosomal recessive primary microcephaly (MCPH) __ a neurodevelopmental disorder __ is characterized by congenital reduction in head circumference by >3SD from gender and age appropriate mean and some degree of intellectual disability. To date, twenty four causative genes have been reported for MCPH. In this study, the genetic analysis of three Pakistani families through homozygosity mapping and next generation sequencing revealed one known and one novel mutations in already known MCPH genes. Juvenile Neuronal Ceroid Lipofuscinosis (JNCL) is a rare neurodegenerative disorder of childhood, which is characterized by progressive visual impairment proceeding to blindness, seizures, cognitive decline and early death usually in the 2nd or 3rd decade of life. Here, one family diagnosed with JNCL was investigated through gene panel (Epiddasd545) sequencing that revealed a novel mutation. This was the first JNCL report from Pakistani population. Charcot-Marie-Tooth (CMT) disease is a neuromuscular disorder characterized by progressive distal muscle atrophy and weakness, foot deformity, sensory loss at distal regions and decreased or absent reflexes. It is a genetically heterogeneous; at least 46 different causative-genes have been reported for CMT so far. In this study, one CMT family was investigated through whole exome sequencing that revealed a novel causative mutation. The fourth disorder, Infantile ascending hereditary spastic paraplegia (IAHSP), is a progressive motor neuron disease characterized by spastic paraplegia of lower limbs in the first 2 years, anarthria, dysphagia and tetraplegia during 1st decade, feed difficulties, wheel-chair dependency and severe tetraparesis manifestations in the 2nd decade of life. Herein, one IAHSP family was investigated through next generation sequencing, the genetic analysis of which revealed a novel mutation. The findings in this study from the investigated Pakistani families expand the mutation spectra, as well as, highlight the diversity of these phenotypes through detailed clinical characterization. This knowledge will provide better understanding to related disease mechanisms and insights for development of therapeutic and preventive interventions.